Synthesis, structural and spectroscopic characterization of defect-rich forsterite as a representative phase of Martian regolith

Jundullah Hanafi, M.I.; Bastonero, L.; Murshed, M.M.; Robben, L.; Dononelli, W.; Kirsch, A.; Marzari, N.; Gesing, T.M.

doi:10.1107/S2052252524009722

research papers

IUCrJ

Volume 11| Part 6| November 2024| Pages 977-990

ISSN: 2052-2525

https://doi.org/10.1107/S2052252524009722

MATERIALS | COMPUTATION

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Synthesis, structural and spectroscopic characterization of defect-rich forsterite as a representative phase of Martian regolith

Muchammad Izzuddin Jundullah Hanafi,^a,^b Lorenzo Bastonero,^b,^c Mohammad Mangir Murshed,^a,^b ^* Lars Robben,^a,^b Wilke Dononelli,^b,^c Andrea Kirsch,^d Nicola Marzari ^b,^c and Thorsten M. Gesing ^a,^b

^aUniversity of Bremen, Institute of Inorganic Chemistry and Crystallography, Leobener Straße 7, D-28359 Bremen, Germany, ^bUniversity of Bremen, MAPEX Center for Materials and Processes, Bibliothekstraße 1, D-28359 Bremen, Germany, ^cBremen Center for Computational Materials Science and Hybrid Materials Interfaces Group, Am Fallturm 1, D-28359 Bremen, Germany, and ^dUniversity of Copenhagen, Department of Chemistry and Nanoscience Center, Universitetsparken 5, Copenhagen 2100, Denmark
^*Correspondence e-mail: murshed@uni-bremen.de

Edited by P. Lightfoot, Formby, Liverpool, United Kingdom (Received 12 August 2024; accepted 3 October 2024; online 28 October 2024)

Regolith draws intensive research attention because of its importance as the basis for fabricating materials for future human space exploration. Martian regolith is predicted to consist of defect-rich crystal structures due to long-term space weathering. The present report focuses on the structural differences between defect-rich and defect-poor forsterite (Mg₂SiO₄) – one of the major phases in Martian regolith. In this work, forsterites were synthesized using reverse strike co-precipitation and high-energy ball milling (BM). Subsequent post-processing was also carried out using BM to enhance the defects. The crystal structures of the samples were characterized by X-ray powder diffraction and total scattering using Cu and synchrotron radiation followed by Rietveld refinement and pair distribution function (PDF) analysis, respectively. The structural models were deduced by density functional theory assisted PDF refinements, describing both long-range and short-range order caused by defects. The Raman spectral features of the synthetic forsterites complement the ab initio simulation for an in-depth understanding of the associated structural defects.

Keywords: Martian forsterite; crystal structures; defects; DFT–PDF; Raman spectroscopy; X-ray powder diffraction; ball milling.

CCDC references: 2391997; 2391998; 2391999; 2392000; 2392001; 2392002; 2392003; 2392004; 2392005; 2392006; 2392007

1. Introduction

In recent years, knowledge about Martian regolith has drastically increased due to the availability of in-situ X-ray diffraction data from the Mars Science Laboratory (MSL) on the Rover Curiosity (Bish et al., 2013 ; Achilles et al., 2017 ; Vaniman et al., 2014 ). The analysis of these diffraction data estimated an amorphous fraction of approximately 28 to 45 wt% in the Martian regolith (Certini et al., 2020 ; Achilles et al., 2017; Vaniman et al., 2014; Demidov et al., 2015 ; Bish et al., 2013). A notable amorphous phase content in Martian regolith indicates significant space weathering due to extreme environmental conditions (Certini et al., 2020). Space weathering is the alteration of exposed surfaces via their interaction with the space environment (Bennett et al., 2013 ). It is a combination of mechanical weathering caused, for example, by meteorite impacts as well as radiation weathering from high-energy solar wind radiation. The former process can be simulated by ball milling (BM) of terrestrial materials in the laboratory (Yu et al., 2022 ).

Olivine-type forsterite (Mg₂SiO₄) is one of the major phases found in the crystalline part of Martian regolith (Bish et al., 2013; Achilles et al., 2017). Bish et al. (2013) reported it to be comprised of approximately 22.4 wt% (Mg_0.62Fe_0.38)₂SiO₄, known as forsteritic olivine. The term can be understood from the forsterite–fayalite [(Mg_1−xFe_x)₂SiO₄] solid solution due to higher Mg content compared with Fe, which was found in Martian soil from the Rocknest Aeolian bedform in the Gale crater. Similarly, Achilles et al. (2017) found approximately 25.8 wt% forsteritic olivine [(Mg_0.56Fe_0.44)₂SiO₄] in Martian soil of the Namib dune named Gobabeb.

For future use of regolith as a basis to fabricate metals or building materials for human space explorations, a precise analysis of the different defects present in forsterites is of crucial importance. The defect-rich forsterite is expected to have lower formation energy, hence may be desirable for more efficient processing of fabrication in space.

Forsterite belongs to planetary and terrestrial rock-forming minerals (Liu et al., 2022 ; Váci et al., 2020 ) and is known for its capability of catalyzing reactions in interstellar dust (Campisi et al., 2024 ). Forsterite is the magnesium endmember of the olivine solid solution (Mg_1−xFe_x)₂SiO₄ (Jundullah Hanafi et al., 2024 ; Rösler, 1991 ) and crystallizes in the orthorhombic space group Pbnm (Fujino et al., 1981 ; Müller-Sommer et al., 1997 ; Lager et al., 1981 ). The structure (Fig. 1) consists of 1D octahedral chains running parallel to the crystallographic c axis, comparable to those found in the mullite-type phase (Angel & Prewitt, 1986 ; Bowen et al., 1924 ; Cong et al., 2010 ; Fischer et al., 2009 ; Gogolin et al., 2020 ). In the mullite-type phase, these octahedral chains are bridged by double tetrahedra or other double units in the ab direction (Murshed et al., 2012 ; Schneider et al., 2012 ), whereas in olivine, single (SiO₄)⁴⁻ tetrahedra link the octahedral chains in the a direction, where the tetrahedrally coordinated oxygen atoms are shared by three octahedrally coordinated cations (Zampiva et al., 2017 ). The respective link in the b direction is realized by two non-equivalent Mg octahedral sites: the first site (M1, chain octahedra) has inversion symmetry, while the other site (M2, linking octahedra) possesses mirror symmetry (Yang et al., 2006 ). Both sites can be occupied by various cations, forming either rich solid solutions or other endmembers such as fayalite [Fe₂SiO₄ (Hanke, 1965 ; Kudoh & Takeda, 1986 ; Hazen, 1977 )], tephroite [Mn₂SiO₄ (Fujino et al., 1981)], larnite [Ca₂SiO₄ (Czaya, 1971 )], liebenbergite [Ni₂SiO₄ (Della Giusta et al., 1990 ; Lager et al., 1981)] and cobalt olivine [Co₂SiO₄ (Morimoto et al., 1974 ; Müller-Sommer et al., 1997)], which enable a wider spectrum of elements extractable from a regolith matrix.

Figure 1
Crystal structure of Mg₂SiO₄ (forsterite).

Forsterite can be synthesized through a variety of synthesis methods including the solution combustion technique (Naik et al., 2015 ; Mondal et al., 2016 ; Prashantha et al., 2011 ), the sol–gel method (Ni et al., 2007 ), mechanical activation followed by heat treatment (Fathi & Kharaziha, 2008 , 2009 ; Tavangarian & Emadi, 2010 ) and reverse strike co-precipitation (RSC) (Zampiva et al., 2017). Despite many studies on the synthesis yielding pure forsterite, to the best of our knowledge there are no reports on mechanically induced defect-rich forsterites and their associated crystal structures. Defects are commonly defined as a considerable extent of irregularities in the crystal structure (Wagner, 1977 ), for example, vacancies or dislocated atoms (see Fig. S1 of the supporting information). In an X-ray diffraction pattern, typical strain broadening and lower absolute intensities are expected for defect-rich crystallites (Ungár, 2004 , Chauhan & Chauhan, 2014 ), often accompanied by reflection broadening due to crystallite size effects (Scherrer, 1918 ; Gesing & Robben, 2024 ). Similarly, broadening of Raman peaks suggests disordered structures in defect-rich materials (Demtröder, 2008 ; Gouadec & Colomban, 2007 ). In addition to Rietveld analysis of reciprocal-space X-ray powder diffraction (XRPD) data, real-space investigations of defects and local structures are widely performed by pair distribution function (PDF) analysis (Bini et al., 2012 ; Malavasi et al., 2011 ; Proffen et al., 2003 ).

The present work focuses on the synthesis and characterization of forsterite and its mechanical post-treatment to induce various defect concentrations. The derived defect-structure model can serve as a structural representative for the analysis of Martian regolith. To achieve this objective, Mg₂SiO₄ samples were first synthesized by two different routes: the RSC method and mechanical activation using high-energy BM with subsequent calcination. In a second step, mechanical post-treatment was performed to obtain defect-rich forsterite. We present a detailed comparison of structural features between the samples using Raman, XRPD and X-ray total scattering techniques. In addition, density functional theory (DFT) is used to optimize defect-rich structures and compare their thermodynamic stability. Finally, the DFT-supported PDF analysis (DFT–PDF) is used to refine the defective structural models.

2. Materials and methods

2.1. Synthesis of defect-poor forsterite

2.1.1. Reverse strike co-precipitation synthesis

Magnesium nitrate hexahydrate [Mg(NO₃)₂·6H₂O, 99.9 %] and tetraethyl orthosilicate (TEOS, 98 %) were purchased from VWR Chemicals and used as received. Similar to a typical RSC synthesis (Zampiva et al., 2017), stoichiometric amounts of Mg(NO₃)₂·6H₂O and TEOS were dissolved in a solution of 40 ml of ethanol and 3 ml of HNO₃ (≥65 %) under magnetic stirring for 1 h. The precursor solution was slowly dripped into 50 ml of 25 % NH₄OH under continuous stirring. The base solution formed a colloid while the precursor solution was being dripped, forming a white precipitate. Simultaneously, several drops of concentrated NH₄OH were added to maintain pH > 8. Thereafter, the precipitate was centrifuged at 60 Hz for 5 min. The supernatant was removed, and ethanol was used to wash the precipitated powder. The centrifugation was repeated three times. Finally, the precipitated solid was placed in a furnace at 473 K for 16 h. The resulting solid was ground in a mortar and calcined at 1373 K for 1 h after reaching the temperature with heating and cooling rates of 15 and 5 K min⁻¹, respectively. The powder attained is designated RFO (RSC synthesis forsterite).

2.1.2. Ball milling synthesis

MgO and amorphous SiO₂ powders were used as starting materials. MgO (>97 %) was purchased from Merck and used as received. Amorphous SiO₂ was obtained from hydrolysis of TEOS (De et al., 2000 ). Forsterite was synthesized by mechanical activation with a high-energy ball mill (Emax-type, RETSCH GmbH). Stoichiometric amounts of the binary oxides were mixed together with 60 g tungsten carbide (WC) balls (2 mm diameter) and placed in a WC grinding jar. The ball-to-powder weight ratio was set to 30:1. The powder was milled for 3 h with different rotational frequencies (7, 12.5 and 15 Hz). Finally, the milled powder was collected from the grinding jar and heated in a corundum crucible at 1373 K at a heating rate of 15 K min⁻¹. After a reaction period of 1 h, the powder was cooled to room temperature at a cooling rate of 5 K min⁻¹. The Mg₂SiO₄ pristine forsterite (PFO) powder attained was ground and further used for characterization.

2.2. Synthesis of defect-rich and healed forsterite

Defect-rich forsterite was prepared by crushing PFO by BM. PFO (1 g) was placed into the grinding jar with 20 g WC balls. The powder was milled at 15 Hz for 1 h. Thereafter, one half of the milled powder was kept separately and labeled as crushed forsterite (CFO). The other half was calcined at 1373 K for 1 h under air to heal the introduced defects, hence labeled healed forsterite (HFO).

2.3. X-ray powder diffraction

XRPD data collection was carried out on a Bruker D8 Discover diffractometer using Cu Kα_1,2 radiation [λ_Kα₁ = 154.05929(5) pm, λ_Kα₂ = 154.4414(2) pm] in Bragg–Brentano geometry. Data were collected under ambient conditions from 5 to 85° 2θ with a step width of 0.0149° 2θ and a measurement time of 0.3 s per step using a multi-strip LynxEye XE-T detector. XRPD data Rietveld refinements were carried out using TOPAS (version 6.0). During the Rietveld refinements, the background, sample displacement, cell metrics, atomic positions and profile parameters were optimized. The amorphous fraction of the samples was quantified from the degree of crystallinity (DC) as implemented in the TOPAS software. For these calculations it is assumed that the average scattering power of the crystalline fraction of the sample is identical to the scattering power of the X-ray amorphous fraction. The latter could either consist of glassy or quantum-crystalline contributions (Gesing et al., 2022 ). Using the fundamental parameter approach (Cline et al., 2010 ), the apparent average crystallite size (ACS) was calculated from all observed X-ray reflections, which is described as L_Vol(IB) by the TOPAS suite. L_Vol(IB) refers to the volume-weighted mean of the coherently diffracting domain size using the integral breadth for the description of the reflection profile. The respective pseudo-Voigt profile function was deconvoluted into Gaussian and Lorentzian components, describing the ACS and the microstrain (ɛ₀), respectively. To validate these data and to receive information about the crystallite size distribution (CSD), an EnvACS analysis (Gesing & Robben, 2024) was performed. For this, data were collected on a Bruker D8 Advance diffractometer using Cu Kα₁ radiation [λ_Kα₁ = 154.05929(5) pm] in Bragg–Brentano geometry. Data were collected under ambient conditions from 10 to 135° 2θ with a step width of 0.01449° 2θ and a measurement time of 4.8 s per step using a multi-strip LynxEye XE detector. The information deduced during these (classical) Rietveld refinements are, with the exception of the DC, based on the appearance of the Bragg reflections and an ideal arrangement of atoms in the unit cell only (Rietveld, 1969 ). To distinguish these calculations from those using total scattering data, we use the expression Bragg–Rietveld for the classical method. The R_wp given is the weighted profile R factor (residual) of the Bragg–Rietveld refinement. To distinguish the R_wp of Bragg–Rietveld and the R_wp of PDF refinements, the latter is denoted R_PDF.

2.4. Raman spectroscopy

Raman spectra were recorded on a LabRam ARAMIS (Horiba Jobin – Yvon) Micro-Raman spectrometer equipped with a green laser (λ_ex = 532 nm and < 20 mW power). A 50× objective (Olympus) with a numerical aperture of 0.75 provides a focus spot of 865 nm diameter when closing the confocal hole to 200 µm. Each spectrum ranges between 100 and 1200 cm⁻¹ with a spectral resolution of approximately 1.2 cm⁻¹ using a grating of 1800 grooves mm⁻¹ and a thermoelectrically cooled CCD detector (Synapse, 1024 × 256 pixels).

2.5. Theoretical Raman calculations

The theoretical Raman spectra calculations were carried out using the aiida-vibroscopy package (Bastonero & Marzari, 2024 ) which exploits the finite displacements and finite field approach (Souza et al., 2002 ; Umari & Pasquarello, 2002 ), and the AiiDA infrastructure (Huber et al., 2020 ; Uhrin et al., 2021 ) to automate the submission of the simulations and the storage of all the data in a reproducible format. The first-order spectrum was calculated in the non-resonant regime using the Placzek approximation. The peak positions associated with the phonon modes were computed in the harmonic approximation via small displacements of the atomic positions (Togo, 2023 ; Togo et al., 2023 ), whereas the Raman tensors, required for the intensity calculations, were obtained via numerical differentiation of the forces in the application of small electric fields (Bastonero & Marzari, 2024). Computational details can be found in Section 2.8.

2.6. X-ray synchrotron total scattering

Total scattering data were collected using beamline P02.1 at PETRA-III, DESY, Hamburg (Dippel et al., 2015 ) with a fixed energy of 60 keV [λ = 20.734(2) pm]. The beamline was equipped with a Varex XRD 4343CT detector (pixel size 150 × 150 µm, 2880 × 2880 pixels). Each sample was measured in 1 mm Kapton capillaries and exposed to radiation for 300 s within a setup particularly optimized for rapid in-situ measurement. PDF data processing was conducted using the PDFGetX3 software (Juhás et al., 2013 ). For all samples, Q_max was set to 1.95 nm⁻¹. Structure model fitting against PDF data was performed using PDFgui (Farrow et al., 2007 ). During the refinement process, instrumental parameters Q_damp and Q_broad were refined to the CeO₂ standard dataset, and then kept fixed with Q_damp = 0.035693 and Q_broad = 0.001 for all the samples. The scale factor, lattice parameters, atomic displacement parameters (ADPs), atomic motion correlation factor and atomic coordinates were refined. The representative processed data I(Q), S(Q), F(Q) and G(r) of PFO are shown in Fig. S2. Stack plots of I(Q) and S(Q) for all the samples are given in Fig. S3.

2.7. DFT–PDF refinement

Combined DFT–PDF refinements of defective forsterite in the spirit of Dononelli (2023 ) and Kløve et al. (2023 ) were performed. Instead of globally optimizing the structure with the GOFEE algorithm (Bisbo & Hammer, 2020 , 2022 ; Kløve et al., 2023), several types of defects, namely vacancies and Frenkel and Schottky defects, were introduced to each atom site during the simulations. DFT was used as a tool to optimize every defect-type structure to their local minimum in the potential energy surface. The geometry-optimized structures were further optimized with a BFGS algorithm by considering the G(r) data from measurements and minimizing the R_PDF. Finally, the structures were refined against the experimental data using PDFgui. The schematic workflow of DFT–PDF refinements is illustrated in Fig. 2.

Figure 2
Schematic workflow maintained during the DFT–PDF refinement for different forsterite structures.

Local structure optimizations have been performed using the electronic structure code GPAW (Enkovaara et al., 2010 ) in the framework of the atomistic simulation environment (Larsen et al., 2017 ). The exchange-correlation interaction was treated by the generalized gradient approximation (GGA) using the Perdew–Burke–Ernzerhof functional (Perdew et al., 1996 ) with a 3 × 5 × 3 k-points sampling of Monkhorst & Pack (1976 ). Note that these calculations were not meant to provide very precise energetics or exact bond lengths. All structures optimized with such settings are later post-processed in PDF–Rietveld refinements to fit to experimentally observed bond lengths.

2.8. Energy calculations

To verify the favorite defective intrinsic candidate, the ab initio formation energy was investigated using DFT calculations. Exploiting the supercell approach, the defect formation energy in a charge state q can be computed as (Zhang & Northrup, 1991 ; Van de Walle et al., 1993 ; Alkauskas et al., 2011 ; Freysoldt et al., 2014 ):

$[E^f[X;q] = E[X,q] - E[{\rm bulk}] - \textstyle \sum_i {n_i}{\mu _i} + q\left(\varepsilon_{\rm v} + \varepsilon_{\rm F} \right),]$

where E[X, q] is the total energy of the supercell calculation of defect X in the charge state q and E[bulk] is the total energy of the pristine crystal structure scaled to match the size of the defective supercell. Each defect is referenced to a chemical potential μ_i corresponding to its species i, while the integer n_i indicates the atoms of type i in excess (n_i > 0) or removed (n_i < 0). For charged states, the chemical potential for the extra electrons is given by the Fermi energy ɛ_F with respect to the valence band maximum ɛ_v of the pristine bulk supercell (Komsa et al., 2012 ). The Fermi energy can be found by the condition of charge neutrality at a specific temperature when all the relevant defects are considered. In the following we consider ɛ_F = 0. To understand the defect formation in the diluted limit (very low defect concentrations), an additional correction term needs to be added due to the periodic boundary conditions, which is described in more detail in the supporting information.

Different defect types along with their nominal and neutral charge states, as well as both relaxed and non-relaxed geometries of the supercells, were thoroughly investigated. Four different supercell sizes of 2 × 1 × 2, 3 × 1 × 2, 3 × 2 × 2 and 3 × 3 × 2 were selected, as well as the single unit cell. For the interstitials, an algorithm introduced by Zimmermann et al. (2017 ) was used to find suitable atomic positions; 11 different positions were found for each species as possible candidates. Interestingly, the interstitials proposed by this pure geometric analysis for the magnesium atoms are found to be in tetrahedral coordination, as found in Walker et al. (2009 ), but here without the explicit energy calculation. The vacancies were instead generated using the space-group symmetries of forsterite, which greatly limits the number of positions.

To carry out the calculations, the Quantum ESPRESSO package (Giannozzi et al., 2009 , 2017 , 2020 ) was used and the PBEsol (Terentjev et al., 2018 ) functional was employed using pseudo-potentials from the precision SSSP library (version 1.1; Prandini et al., 2018 ). The wavefunction and charge-density expansions were truncated with an energy cutoff of 80 and 960 Ry, respectively. The Brillouin zone was sampled using a uniform Monkhorst–Pack grid with a 4 × 2 × 3 k-points mesh. The geometry and atomic positions of forsterite were therefore relaxed until the total energy and forces were below 10⁻⁶ Ry atom⁻¹ and 10⁻⁵ Ry Bohr⁻¹, respectively. Supercell calculations were carried out using a gamma-point sampling, after having verified that the total energy changed by only 2 meV atom⁻¹ for a 2 × 1 × 2 supercell. The geometry and the atomic positions of each defective supercell were optimized with lower thresholds for the total energy and forces of 10⁻⁴ Ry atom⁻¹ and 10⁻³ Ry Bohr⁻¹, respectively.

3. Results and discussion

3.1. Synthesis

Impure forsterite was obtained from BM synthesis with 7 (IFO-7) and 12.5 Hz (IFO-12). On the other hand, PFO was successfully obtained by RSC synthesis (Zampiva et al., 2017) (RFO) and BM synthesis at 15 Hz (PFO). Both synthesis techniques yielded white forsterite powder. To introduce defects into the material, the attained PFO powder was mechanically post-processed by BM at 15 Hz for 1 h resulting in CFO. CFO possesses a slightly grayish color, either due to trace amounts of WC abraded from the mill, or suggesting the presence of defects. However, we estimated the amount to be lower than the detection limit [0.5(1) wt%] as we cannot observe any WC signal in the XRD (nor Raman) data. Finally, a small amount of CFO was re-calcined at 1373 K and a white powder of HFO with the expected lower defect concentrations was obtained. The synthesized samples and their respective IDs are listed in Table 1. Detailed information about phase quantification for impure forsterites determined from Rietveld refinements is provided in the Section 3.2.

Table 1
List of synthesized samples and their abbreviations

Sample ID	Material
RFO	RSC synthesis forsterite
IFO-7	Impure forsterite from 7 Hz BM
IFO-12	Impure forsterite from 12.5 Hz BM
PFO	Pristine forsterite from 15 Hz BM
CFO	Crushed forsterite (post-processed PFO)
HFO	Healed forsterite (re-calcined CFO)

3.2. X-ray powder diffraction

XRPD data Bragg–Rietveld refinements confirm that IFO-7 contains impurities of MgO, MgSiO₃ and SiO₂ in two modifications (α-cristobalite and α-quartz), whereas IFO-12 possesses only MgO as a minor impurity. This indicates that the BM frequencies of 7 and 12.5 Hz are not sufficient to form an intimate mixture of the reactants before the calcination process. On the contrary, pure forsterite was obtained from RSC (RFO) and BM (PFO) synthesis at 15 Hz. All reflections in the diffraction pattern of both samples can be indexed to olivine-type Mg₂SiO₄ with the space group Pbnm (Müller-Sommer et al., 1997). The mechanically treated sample (CFO) is also characterized as a pure forsterite. However, broadening of the Bragg reflections along with significantly lower intensity maxima is observed, as shown in Fig. 3. Moreover, CFO exhibits notably lower ACS [25(1) nm] and DC [60(5) %] compared with those of PFO [ACS = 77(1) nm and DC = 98(5) %]. Inversely, the microstrain is increased from 0.031(1) to 0.140(4) upon BM. The re-calcination process of CFO led to re-crystallization, forming a crystalline forsterite with an ACS, ɛ₀ and DC of 77(2) nm, 0.140(4) and 90(5) %, respectively, like those of PFO. Comparable values are observed when analyzing the ACS using the EnvACS (Gesing & Robben, 2024) approach. Nevertheless, the CSD provides additional information on the defect formation and the respective defect healing. For the synthesized samples (RFO and PFO) the CSD is narrow whereas a much broader CSD is observed for CFO. This is not surprising, as it is assumed that not only are defects introduced, but during the reduction of the ACS, not all crystallites are homogeneously destroyed due to crystallite cracking. For the heated CFO portion resulting in the HFO sample, it is obvious that the distribution narrows again by a factor of two but did not reach the narrow distribution of the as-synthesized PFO. Interestingly, meaningful results could only be obtained by also refining a scale factor in the EnvACS (Gesing & Robben, 2024) approach, which would represent the distribution of two different phases, namely the crystalline forsterite and the amorphous forsterite, respectively. The scale factors obtained correlate quite well with the DC obtained by the Bragg–Rietveld refinements. A complete list of XRPD characterization results is given in Table 2. The stack plots of XRPD patterns of all samples can be seen in Fig. S4.

Table 2
ACS and microstrain (ɛ₀) of forsterites, and the DC of the synthesized samples obtained from Bragg–Rietveld refinements of XRPD data

Additionally, the ACS and the CSD factor, correlating the smallest (0.01) and broadest (1) distribution of spherical crystallites, are given. Both values were refined with a fixed to 1 and a variable scale factor, considering perfect and reduced DC, respectively.

	Bragg–Rietveld					EnvACS
Sample ID	Phase fraction /%		ACS /nm	ɛ₀	DC /%	ACS /nm	CSD factor	Scale factor
IFO-7	Mg₂SiO₄	62(2)	58(1)	0.048(2)	95(5)	–	–	–
	MgO	23(2)	–	–	–	–	–	–
	MgSiO₃	8(2)	–	–	–	–	–	–
	SiO₂ α-cristobalite	6(2)	–	–	–	–	–	–
	SiO₂ α-quartz	1(2)	–	–	–	–	–	–
IFO-12	Mg₂SiO₄	98(2)	61(1)	0.053(5)	93(5)	–	–	–
IFO-12	MgO	2(2)	–	–	–	–	–	–
RFO	Mg₂SiO₄	100(2)	89(1)	0.027(1)	95(5)	85.5(5)	0.01(1)	1
RFO						87.1(5)	0.01(1)	0.98(1)
PFO	Mg₂SiO₄	100(2)	77(1)	0.031(1)	98(5)	88.3(5)	0.01(1)	1
PFO						89.0(5)	0.01(1)	0.99(1)
CFO	Mg₂SiO₄	100(2)	25(1)	0.140(4)	60(5)	33.3(2)	0.01(1)	1
CFO						57.6(3)	0.17(1)	0.68(1)
HFO	Mg₂SiO₄	100(2)	77(2)	0.046(1)	90(5)	74.9(6)	0.01(1)	1
HFO						75.4(4)	0.07(1)	0.95(1)

Figure 3
XRPD data Rietveld plots of different forsterites.

Refined forsterite crystal data, along with comparative literature (Smyth & Hazen, 1973 ), are presented in Table S1 of the supporting information. The respective Bragg–Rietveld refinements converged with lower R_wp values for RFO (11 %) and PFO (11 %) compared with CFO (15 %) and HFO (15 %) (see Fig. 3 and Table S1). Moreover, structure refinements indicate that RFO and PFO can be classified as defect-poor forsterites, as their refined atomic positions possess only small changes (Δz ≤ 0.003) compared with pristine forsterite. In contrast, noticeable structural changes are observed in both HFO and CFO. As an example, the O(3) atom in HFO slightly deviates from its initial position (Δz ≤ 0.010) while CFO shows even stronger changes (Δz ≤ 0.018). The strength of these observed structural changes is proportional to the expected defect concentration in the crystal, which is described in more detail in Section 3.3.

3.3. Raman spectroscopy

The factor group analysis predicts that orthorhombic Mg₂SiO₄ has 84 normal vibrational modes (11 A_g + 11 B_1g + 7 B_2g + 7 B_3g + 10 A_u + 10 B_1u + 14 B_2u + 14 B_3u), among which A_g, B_1g, B_2g and B_3g modes are Raman active (Iishi, 1978 ; Hofmeister, 1987 ). Raman spectra of different forsterites are shown in Fig. 4. Peak fitting was performed for each experimental spectrum, representatively shown in Fig. S5 for PFO. The peak maxima along with comparative experimental reference data (Kolesov & Geiger, 2004 ) and theoretical calculations (Stangarone et al., 2017 ; McKeown et al., 2010 ) are given in Table S2. The observed band frequencies are in good agreement with those of the reported ones (Kolesov & Geiger, 2004; Stangarone et al., 2017; McKeown et al., 2010) and our own theoretical calculation. Typically, Raman spectra of olivine-type Mg₂SiO₄ can be classified into three regions: <400 cm⁻¹, 400–700 cm⁻¹ and >700 cm⁻¹. The lower region bands are attributed to the vibrational modes from Mg [M(2) site] and negligible contribution from lighter silicon (Stangarone et al., 2017; Chopelas, 1991 ). Peaks between 400 and 700 cm⁻¹ are mainly contributed from bending motion of the Mg(2)—O bonds (Stangarone et al., 2017). The high-frequency region (>700 cm⁻¹) can be attributed to the internal Si—O stretching vibrations of the SiO₄ tetrahedra (Chopelas, 1991; Stangarone et al., 2017). The most dominant characteristic of the forsterite spectral range lies at around 820 and 860 cm⁻¹ (Chopelas, 1991; Iishi, 1978; Wang et al., 1995 , 2004 ).

Figure 4
Raman spectra of different forsterites collected under ambient conditions and the PBEsol calculation (left). Magnified view of the high-frequency region (right); vertical dashed lines are a guide for the eye.

Some vibrational features from optical phonons are clearly distinguishable between the defect-poor samples (RFO and PFO) and the defect-containing samples (CFO and HFO). Global red shifts of ±1 cm⁻¹ along with peak-broadening (ΔFWHM ≤ 2 cm⁻¹) are observed in HFO. Moreover, greater red shifts of approximately 3(1) cm⁻¹ as well as peak broadening (ΔFWHM ≤ 4 cm⁻¹) are observed in CFO. The dominant two intense modes related to Si—O are further shifted to 825(1) and 857(1) cm⁻¹, with FWHMs of 11(1) and 13(1) cm⁻¹, respectively. In general, peak shifting and broadening in Raman spectra can be attributed to crystallite size effects and the degree of disorder in a structure (Swamy et al., 2006 ; Islam et al., 2005 ; Gouadec & Colomban, 2007; Demtröder, 2008). Here, the Raman peak broadening and shifts are proportional to the defect concentration in the structure. This finding further indicates that the CFO sample exhibits local structural disorder with the highest concentration.

3.4. PDF analysis

To further investigate the defects and local structures of the samples, total scattering experiments were carried out (beamline P02.1 at PETRA-III, DESY, Hamburg). The analysis of the total scattering data allows the extraction of information from both Bragg and diffuse scattering contributions. The Bragg scattering contribution can be analyzed by the conventional approach in reciprocal space and provides information on the average and long-range periodic structure, whereas the diffuse scattering which lies between and beneath the Bragg reflections (Egami & Billinge, 2003 ) yields information regarding the short-range order and local structure deviations. Each measurement was integrated, background corrected and Fourier transformed to obtain the reduced PDF G(r). The G(r) describes the probability of finding two atoms separated by a distance of r (Teck et al., 2017 ). Although the observed PDFs [G(r)] of RFO, PFO and HFO are very similar, that of CFO shows significant discrepancies (e.g. broadened signals, clear shoulders and lower intensities) as shown in Fig. 5.

Figure 5
Observed G(r) for different forsterites.

Defect-free, symmetry-constrained structural models of Mg₂SiO₄ were fitted against the experimental PDFs using a small-box modeling approach including symmetry constraints (PDF–Rietveld). Representative PDF–Rietveld refinements of the investigated forsterites are shown in Fig. 6. The refinements of CFO converged with R_PDF = 26 %, significantly higher than those of RFO, PFO (R_PDF = 16 %) and HFO (R_PDF = 18 %). The higher R_PDF of CFO indicates that a simple PDF–Rietveld refinement using an ideal average crystal structure model struggles to describe the defect-rich local nature of the post-milled sample. As such, a more advanced defect-rich structure model based on DFT–PDF refinements is proposed in this work, described in more detail in Section 3.5.

Figure 6
Representative PDF–Rietveld refinement plots of PFO and CFO in the long (left) and short to medium (right) range.

The bond lengths obtained from Bragg–Rietveld and PDF–Rietveld refinements are compared in Table S3 within each of the forsterite samples. Based on Bragg–Rietveld refinements, the average bond lengths [further noted as 〈Mg(1)—O〉, 〈Mg(2)—O〉 and 〈Si—O〉] of RFO and PFO are virtually identical, whereas the bond lengths of HFO only differ by a maximum of 0.1 pm. Interestingly, 〈Mg(1)—O〉 and 〈Mg(2)—O〉 of CFO are slightly longer than those of the defect-poor forsterites [Δ1 pm for 〈Mg(1)—O〉 and Δ0.5 pm for 〈Mg(2)—O〉]. On the contrary, the 〈Si—O〉 of CFO is the shortest among all forsterites (Δ2 pm). As a consequence, the bond valence sum (BVS) (Brese & O'Keeffe, 1991 ) of Si in the CFO is found to show over bonding [4.19(2) v.u.].

Unlike the Bragg–Rietveld refinements, which suggest shorter 〈Si—O〉 bond lengths for CFO, the 〈Si—O〉 bonds determined through PDF–Rietveld refinements consistently display similar values. This results in an Si BVS of 3.84(3) v.u. across all forsterites. We attribute the different interatomic distances obtained from PDF–Rietveld and Bragg–Rietveld analyses to ACS limitation effects of the short synchrotron wavelength due to maximal observable average crystallite size [MOACS (Gesing & Robben, 2024)] and the repeated observation. Furthermore, Rietveld refinements often describe local distortions, such as atom displacement, with an increase in the Debye–Waller factor (Abeykoon et al., 2009 ).

3.5. DFT–PDF refinement

3.5.1. Single-phase refinement

Small box (single unit cell): in Section 3.4 the fitting results against crystalline Mg₂SiO₄ for all samples have been given. To receive a better fit of the structure model against the experimental PDF data of CFO, DFT-assisted PDF refinements (DFT–PDF) were implemented. As an initial step, a geometry-optimized structure model of Mg₂SiO₄ without defects (GOSWD) was selected. Single-phase DFT–PDF refinements using this symmetry-free structure model showed a slightly better fit (R_PDF = 23 %) compared with the original (symmetry-constraint) model for defect-free, crystalline Mg₂SiO₄ (R_PDF = 26 %). Then, 17 structure models containing vacancy, Schottky and Frenkel defects (see Fig. S1 of the supporting information) were generated from the DFT–PDF workflow (Section 2.7). Furthermore, each DFT–PDF-generated structure model was individually selected for DFT–PDF refinement. Overall, the new defective structure models gave an R_PDF in the range 22–28 %, where defects involving oxygen show the lowest values.

Large box (2 × 2 × 2 unit cells): to realize lower concentrations of defects, larger systems (2 × 2 × 2 unit cells) were employed. To begin with, DFT–PDF refinements of a pristine 2 × 2 × 2 structure without further structure variation gave R_PDF = 37 %, while its GOSWD converged with R_PDF = 27 %. The significant mismatch observed between these refinements offers additional indications that the crystalline structure is unable to accommodate the defect-rich characteristics of the CFO sample. As before, 17 defective 2 × 2 × 2 models containing vacancy, Frenkel and Schottky defects were generated from DFT–PDF optimization. The refinements converged with an R_PDF in the range 19–22 %. Nine of them (four different vacancies, two Frenkel and three Schottky defects) have almost identical R_PDF values of 19 %.

Point defect (2 × 1 × 2 unit cells): in a third approach, charge defect analysis was in focus. Both charged and neutral defects are considered for this calculation, for which the size of 2 × 1 × 2 unit cells was selected. In total, ten defective 2 × 1 × 2 structure models were investigated: Mg interstitial and vacancy, O interstitial and vacancy, as well as Si interstitial. The refinements converged with R_PDF = 25–28 %, showing trends like the values for the single unit cells used. Table S4 summarizes the R_PDF values of all defective structure candidates.

3.5.2. Stability of defective structure candidates

The calculated formation energies of the defective structure candidates are reported in Table S4. Positive numbers indicate metastable or unfavorable structures, whereas negative values indicate spontaneous or favorable formation of the structures. It can be observed that most of the structures have positive formation energies. Schottky defects in particular show the highest formation energies (>8 eV) and therefore those structures should be discarded as possible candidates. Table 3 shows selected defective structure candidates (CIFs can be found in the supporting information) with formation energies <5 eV. Note, the formation energies in Table 3 were not corrected to account for the formation of a single defect in the dilute limit, since we expect high defect concentrations in CFO. A complete list of formation energies at different defect concentrations, to extrapolate the dilute limit, can be found in Table S5.

Table 3
Selected defective structure candidates along with their symmetry analysis upon cell relaxation, formation energy and R_PDF values

GOSWD = geometry-optimized structure without defect, F = Frenkel, I = interstitial, V = vacancy. The structure model marked with * falls back to the pristine structure upon optimization.

Defective structure candidate	Unit-cell size	Symmetry analysis	Formation energy /eV	R_PDF /%
GOSWD	1	Pbnm (62)*	0.01	23
Mg(1) F	1	P1 (2)	2.98	25
Mg I +0	2 × 1 × 2	P1 (1)	3.73	27
Mg I +2	2 × 1 × 2	P1 (1)	−5.25	27
O I +0	2 × 1 × 2	P1 (1)	1.37	27
O V +2	2 × 1 × 2	P1 (1)	1.49	27
Si I +4	2 × 1 × 2	P1 (1)	−9.07	28

The interpretation of formation energies is not straightforward, since they strongly depend on the calculation scheme and the defect concentration/size of the simulation cell. Earlier studies by Walker et al. (2009, 2003 ) did not consider the possible interaction between the defects (i.e. they performed a `mere' energy difference, hence the interaction of charged defects is long-ranged and sizeable). As an improvement, we extrapolated the free energy of formation to the infinite volume, i.e. to the dilute limit (using the formula shown in the supporting information). Nevertheless, similarly we found that Mg(1) Frenkel defects are energetically stable with a formation energy of 2.98 eV. In addition, we performed vacancy and interstitial supercell calculations with charged point defects and found comparable results to the available literature (Walker et al., 2009, 2003). At high defect concentrations, both Si⁴⁺ and Mg²⁺ interstitials seem to be the most energetically favorable. However, oxygen vacancies are found to be the most favorable defects in the extrapolated dilute limit (very low concentration). This may be due to the usage of a GGA functional, which tends to underestimate the bond strength of the oxygen molecule. Table S5 summarizes the formation energy of charge defect structures computed using different fixed supercell sizes and extrapolated dilute limits.

3.5.3. Multi-phase refinement

Ultimately, all structure motifs with favorable energy (as listed in Table 3) were used in combined multi-phase refinements. In principle, the respective defective structure is treated as a secondary phase alongside the crystalline one (GOSWD). The refined defective phases showing a negative scale factor were removed one at a time from the refinements. The best fit is finally achieved using a combination of a single unit cell of GOSWD and Mg(1) Frenkel, along with 2 × 1 × 2 Mg²⁺ interstitial defect structures which converge to R_PDF = 18 %, as illustrated in Fig. 7. This fitting indicates that CFO consists of 67(3) wt% GOSWD, 23(3) wt% Mg Frenkel and 10(3) wt% of Mg²⁺ interstitial. The optimized defective forsterite structure models are shown in Fig. 8. Note, however, that any defect summarized in Table 3 might be present in defective Mg₂SiO₄, but not in the CFO sample with defects mechanically induced by BM. Although Si⁴⁺ interstitials might be favorable from an energetic point of view, this motif does not improve the PDF fit of CFO. Therefore, the presence of this type of defect is rather unlikely, and is probably prevented by the atmospheric reaction conditions leading to a high concentration of oxygen-rich phases.

Figure 7
Multi-phase DFT–PDF refinement plot of CFO in the long and short to medium (inset) range.

Figure 8
DFT–PDF optimized crystal structures of (a) 2 × 1 × 2 Mg²⁺ interstitial and (b) single unit cell Mg(1) Frenkel defects in comparison with the (c) pristine forsterite structure.

4. Conclusions and outlook

Structural differences between defect-poor and defect-rich forsterite (Mg₂SiO₄) were investigated. Mechanically induced defect-rich forsterite was obtained by BM of defect-poor (pristine) forsterite. Implementing PDF–Rietveld refinements on X-ray synchrotron data indicated a complex disorder structure in the defect-rich forsterite. Raman peak broadening and global red shifts complemented the structural features of the defective phases. The defect-rich structure models were simulated using the DFT–PDF method to better describe the disorder in the local structure. DFT–PDF refinements indicate that post-processed forsterite contains Mg Frenkel-type and Mg²⁺ interstitial defects with concentrations of 23(3) and 10(3) wt%, respectively. DFT calculations confirmed that the defective structure models are energetically stable. This finding is an important starting point to characterize and quantify defect-rich Martian regolith. Further investigations involving a larger number of phases are necessary as a stepwise strategy to structurally describe multi-phase Martian regolith. Additionally, a comparative study between radiation-induced defects and the mechanically induced defects described here would be of high demand to understand the mechanism of space weathering effects.

Supporting information

CCDC references: 2391997; 2391998; 2391999; 2392000; 2392001; 2392002; 2392003; 2392004; 2392005; 2392006; 2392007

Crystal structure: contains datablocks Mg2SiO4_CFO_USI_2121821137_Frenkel_Mg1, Mg2SiO4_CFO_USI_2121821137_GOSWD, Mg2SiO4_CFO_USI_2121821137_Interstitial_Mg_0, Mg2SiO4_CFO_USI_2121821137_Interstitial_Mg_+2, Mg2SiO4_CFO_USI_2121821137_Interstitial_O_0, Mg2SiO4_CFO_USI_2121821137_Interstitial_Si_+4, Mg2SiO4_CFO_USI_2121821137_Vacancy_O_+2, Mg2SiO4_CFO_USI_2121821137, Mg2SiO4_HFO_USI_2121821138, Mg2SiO4_PFO_USI_2121821136, Mg2SiO4_RFO_USI_2121821033. DOI: https://doi.org/10.1107/S2052252524009722/lt5071sup1.cif

Supporting figures and tables. DOI: https://doi.org/10.1107/S2052252524009722/lt5071sup2.pdf

Powder diffraction data. DOI: https://doi.org/10.1107/S2052252524009722/lt5071sup3.zip

Computing details top

magnesium silicate (Mg2SiO4_CFO_USI_2121821137_Frenkel_Mg1) top

Crystal data top

Mg₈O₁₆Si₄	α = 90°
M_r = 562.76	β = 90°
Triclinic, P1	γ = 90°
Hall symbol: P 1	V = 285.47 Å³
a = 4.72942 Å	Z = 1
b = 10.1528 Å	Melting point: not measured K
c = 5.94525 Å

Data collection top

h = →	l = →
k = →

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0.9736	0.0074	0.0048	0.00317
Mg2	0.4948	0.5077	0.0023	0.00317
Mg3	0.4998	0.5063	0.4794	0.00317
Mg4	0.9812	0.2870	0.2722	0.01008
Mg5	0.0001	0.7247	0.7099	0.01008
Mg6	0.4840	0.2167	0.7486	0.01008
Mg7	0.5005	0.7802	0.2616	0.01008
Si1	0.3920	0.1005	0.2616	0.00674
Si2	0.5701	0.9088	0.7440	0.00674
Si3	0.9407	0.4046	0.7268	0.00674
Si4	0.0588	0.5989	0.2153	0.00674
O1	0.6886	0.0677	0.2280	0.05374
O2	0.2875	0.9169	0.7957	0.05374
O3	0.2586	0.4260	0.7642	0.05374
O4	0.6489	0.6069	0.2459	0.05374
O5	0.1860	0.4402	0.2460	0.00892
O6	0.7778	0.5524	0.7205	0.00892
O7	0.7694	0.0576	0.7097	0.00892
O8	0.2584	0.9321	0.2280	0.00892
O9	0.2688	0.1810	0.0108	0.00750
O10	0.6899	0.8259	0.9291	0.00750
O11	0.7392	0.3400	0.9943	0.00750
O12	0.1781	0.6548	0.9925	0.00750
O13	0.6810	0.8250	0.4849	0.00750
O14	0.3136	0.1833	0.4363	0.00750
O15	0.2143	0.6672	0.4531	0.00750
O16	0.7388	0.3363	0.5494	0.00750
Mg8	0.0894	0.4563	0.4747	0.00317

magnesium silicate (Mg2SiO4_CFO_USI_2121821137_GOSWD) top

Crystal data top

Mg₈O₁₆Si₄	α = 90°
M_r = 562.76	β = 90°
Triclinic, P1	γ = 90°
Hall symbol: P 1	V = 290.34 Å³
a = 4.756 Å	Z = 1
b = 10.2035 Å	Melting point: not measured K
c = 5.983 Å

Data collection top

h = →	l = →
k = →

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0.99822	0.98017	0.97427	1.0000
Mg2	0.49368	0.48272	0.96067	1.0000
Mg3	0.01169	0.97974	0.49665	1.0000
Mg4	0.49429	0.46977	0.47276	1.0000
Mg5	0.99378	0.26421	0.23456	1.0000
Mg6	0.99914	0.70453	0.73384	1.0000
Mg7	0.47082	0.21384	0.74895	1.0000
Mg8	0.51793	0.75886	0.22990	1.0000
Si1	0.44111	0.07540	0.21778	1.0000
Si2	0.58066	0.88395	0.74506	1.0000
Si3	0.90518	0.38689	0.72683	1.0000
Si4	0.06964	0.57497	0.23562	1.0000
O1	0.78190	0.08165	0.25000	1.0000
O2	0.23398	0.87440	0.75503	1.0000
O3	0.24389	0.39509	0.71672	1.0000
O4	0.72579	0.56329	0.22887	1.0000
O5	0.22329	0.43161	0.20611	1.0000
O6	0.77945	0.53653	0.71535	1.0000
O7	0.69570	0.03887	0.72470	1.0000
O8	0.28710	0.93374	0.24016	1.0000
O9	0.25267	0.13875	0.02312	1.0000
O10	0.75156	0.81694	0.95708	1.0000
O11	0.78189	0.32007	0.95989	1.0000
O12	0.22027	0.65025	0.02257	1.0000
O13	0.72174	0.81902	0.52252	1.0000
O14	0.39092	0.08863	0.48436	1.0000
O15	0.19867	0.68165	0.41823	1.0000
O16	0.76081	0.30401	0.51973	1.0000

magnesium silicate (Mg2SiO4_CFO_USI_2121821137_Interstitial_Mg_0) top

Crystal data top

Mg₃₃O₆₄Si₁₆	α = 90°
M_r = 2275.36	β = 90°
Triclinic, P1	γ = 90°
Hall symbol: P 1	V = 1162.88 Å³
a = 9.5166 Å	Z = 1
b = 10.2043 Å	Melting point: not measured K
c = 11.9748 Å

Data collection top

h = →	l = →
k = →

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0.586960	0.441180	0.879310	0.008640
Mg2	0.586950	0.441170	0.379320	0.008640
Mg3	0.086960	0.441190	0.879310	0.008640
Mg4	0.086960	0.441180	0.379300	0.008640
Mg5	0.586960	0.441190	0.129310	0.008640
Mg6	0.586960	0.441160	0.629320	0.008640
Mg7	0.086960	0.441160	0.129320	0.008640
Mg8	0.086960	0.441160	0.629310	0.008640
Mg9	0.836950	0.941170	0.879310	0.008640
Mg10	0.836960	0.941180	0.379310	0.008640
Mg11	0.336960	0.941170	0.879300	0.008640
Mg12	0.336960	0.941170	0.379320	0.008640
Mg13	0.836960	0.941180	0.129300	0.008640
Mg14	0.836960	0.941190	0.629330	0.008640
Mg15	0.336960	0.941180	0.129310	0.008640
Mg16	0.336940	0.941180	0.629310	0.008640
Mg17	0.841160	0.217720	0.004310	0.008640
Mg18	0.841150	0.217760	0.504310	0.008640
Mg19	0.341150	0.217750	0.004310	0.008640
Mg20	0.341150	0.217740	0.504320	0.008640
Mg21	0.832750	0.664590	0.254310	0.008640
Mg22	0.832770	0.664600	0.754320	0.008640
Mg23	0.332750	0.664610	0.254310	0.008640
Mg24	0.332770	0.664600	0.754320	0.008640
Mg25	0.591150	0.164600	0.254320	0.008640
Mg26	0.591170	0.164590	0.754320	0.008640
Mg27	0.091160	0.164610	0.254300	0.008640
Mg28	0.091160	0.164610	0.754320	0.008640
Mg29	0.082750	0.717730	0.004310	0.008640
Mg30	0.082760	0.717760	0.504310	0.008640
Mg31	0.582760	0.717760	0.004310	0.008640
Mg32	0.582760	0.717750	0.504310	0.008640
Si1	0.623750	0.035030	0.004310	0.006143
Si2	0.623740	0.035040	0.504310	0.006143
Si3	0.123750	0.035030	0.004310	0.006143
Si4	0.123730	0.035040	0.504330	0.006143
Si5	0.050190	0.847320	0.254320	0.006143
Si6	0.050170	0.847330	0.754330	0.006143
Si7	0.550180	0.847320	0.254320	0.006143
Si8	0.550190	0.847340	0.754340	0.006143
Si9	0.873720	0.347340	0.254310	0.006143
Si10	0.873730	0.347310	0.754320	0.006143
Si11	0.373740	0.347310	0.254310	0.006143
Si12	0.373740	0.347310	0.754300	0.006143
Si13	0.800180	0.535030	0.004310	0.006143
Si14	0.800190	0.535060	0.504300	0.006143
Si15	0.300190	0.535030	0.004310	0.006143
Si16	0.300190	0.535040	0.504300	0.006143
O1	0.952870	0.032840	0.004300	0.016726
O2	0.952930	0.032850	0.504310	0.016726
O3	0.452930	0.032850	0.004310	0.016726
O4	0.452930	0.032860	0.504320	0.016726
O5	0.720990	0.849500	0.254310	0.016726
O6	0.720990	0.849490	0.754300	0.016726
O7	0.220990	0.849500	0.254310	0.016726
O8	0.220980	0.849500	0.754310	0.016726
O9	0.702930	0.349510	0.254310	0.016726
O10	0.702920	0.349500	0.754320	0.016726
O11	0.202920	0.349490	0.254310	0.016726
O12	0.202920	0.349490	0.754310	0.016726
O13	0.970980	0.532850	0.004310	0.016726
O14	0.970990	0.532850	0.504320	0.016726
O15	0.470990	0.532850	0.004310	0.016726
O16	0.470990	0.532860	0.504320	0.016726
O17	0.697800	0.887550	0.004280	0.016726
O18	0.697960	0.887170	0.504310	0.016726
O19	0.197970	0.887160	0.004310	0.016726
O20	0.197960	0.887170	0.504320	0.016726
O21	0.975950	0.995180	0.254320	0.016726
O22	0.975960	0.995190	0.754300	0.016726
O23	0.475960	0.995190	0.254310	0.016726
O24	0.475970	0.995190	0.754320	0.016726
O25	0.947950	0.495180	0.254310	0.016726
O26	0.947960	0.495190	0.754320	0.016726
O27	0.447950	0.495190	0.254310	0.016726
O28	0.447960	0.495190	0.754310	0.016726
O29	0.725950	0.387170	0.004310	0.016726
O30	0.725960	0.387170	0.504310	0.016726
O31	0.225960	0.387170	0.004310	0.016726
O32	0.225960	0.387160	0.504320	0.016726
O33	0.698940	0.104530	0.113430	0.016726
O34	0.698940	0.104520	0.613410	0.016726
O35	0.198950	0.104520	0.113410	0.016726
O36	0.198940	0.104520	0.613410	0.016726
O37	0.974970	0.777830	0.363400	0.016726
O38	0.974970	0.777820	0.863400	0.016726
O39	0.474970	0.777830	0.363420	0.016726
O40	0.474980	0.777840	0.863410	0.016726
O41	0.948950	0.277840	0.145220	0.016726
O42	0.948940	0.277840	0.645220	0.016726
O43	0.448940	0.277830	0.145210	0.016726
O44	0.448940	0.277820	0.645210	0.016726
O45	0.724960	0.604520	0.895210	0.016726
O46	0.724970	0.604520	0.395210	0.016726
O47	0.224970	0.604520	0.895210	0.016726
O48	0.224970	0.604520	0.395210	0.016726
O49	0.974960	0.777830	0.145210	0.016726
O50	0.974980	0.777830	0.645210	0.016726
O51	0.474970	0.777830	0.145210	0.016726
O52	0.474960	0.777840	0.645220	0.016726
O53	0.698890	0.104590	0.895180	0.016726
O54	0.698940	0.104520	0.395220	0.016726
O55	0.198960	0.104530	0.895210	0.016726
O56	0.198940	0.104520	0.395210	0.016726
O57	0.724960	0.604510	0.113410	0.016726
O58	0.724970	0.604530	0.613420	0.016726
O59	0.224960	0.604520	0.113410	0.016726
O60	0.224970	0.604520	0.613410	0.016726
O61	0.948950	0.277830	0.363410	0.016726
O62	0.948940	0.277820	0.863410	0.016726
O63	0.448940	0.277840	0.363420	0.016726
O64	0.448940	0.277840	0.863410	0.016726
Mg33	0.793440	0.999990	0.939500	0.008640

magnesium silicate (Mg2SiO4_CFO_USI_2121821137_Interstitial_Mg_+2) top

Crystal data top

Mg₃₃O₆₄Si₁₆	α = 90°
M_r = 2275.36	β = 90°
Triclinic, P1	γ = 90°
Hall symbol: P 1	V = 1162.91 Å³
a = 9.5167 Å	Z = 1
b = 10.2047 Å	Melting point: not measured K
c = 11.9746 Å

Data collection top

h = →	l = →
k = →

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0.00001	0.00003	0.75005	0.683371
Mg2	0.00005	0	0.25002	0.683371
Mg3	0.50004	0.0001	0.75003	0.683371
Mg4	0.50004	0.00002	0.25	0.683371
Mg5	0.00004	0	0	0.683371
Mg6	0.00004	0.00003	0.5	0.683371
Mg7	0.50005	0	0.00004	0.683371
Mg8	0.50003	0.00001	0.50003	0.683371
Mg9	0.25005	0.49999	0.75001	0.683371
Mg10	0.25006	0.50001	0.25001	0.683371
Mg11	0.75004	0.50002	0.75001	0.683371
Mg12	0.75003	0.5	0.25001	0.683371
Mg13	0.25005	0.50002	0.00002	0.683371
Mg14	0.25002	0.50003	0.50001	0.683371
Mg15	0.75003	0.50002	0.00003	0.683371
Mg16	0.75005	0.50002	0.50001	0.683371
Mg17	0.25425	0.77655	0.87501	0.683371
Mg18	0.25422	0.77657	0.37501	0.683371
Mg19	0.75424	0.77656	0.87501	0.683371
Mg20	0.75424	0.77656	0.37502	0.683371
Mg21	0.24583	0.22348	0.12501	0.683371
Mg22	0.24584	0.22348	0.62499	0.683371
Mg23	0.74584	0.22348	0.12502	0.683371
Mg24	0.74582	0.22348	0.62501	0.683371
Mg25	0.00425	0.72349	0.12501	0.683371
Mg26	0.00424	0.72349	0.62501	0.683371
Mg27	0.50423	0.72346	0.125	0.683371
Mg28	0.50423	0.72346	0.625	0.683371
Mg29	0.49584	0.27655	0.87502	0.683371
Mg30	0.49584	0.27656	0.37501	0.683371
Mg31	0.99584	0.27657	0.87501	0.683371
Mg32	0.99584	0.27656	0.37499	0.683371
Mg33	0.48905	0.2059	0.81036	0.683371
Si1	0.03683	0.5939	0.87501	0.478005
Si2	0.03681	0.59389	0.37503	0.478005
Si3	0.53683	0.59391	0.87502	0.478005
Si4	0.53682	0.59389	0.375	0.478005
Si5	0.46326	0.40614	0.125	0.478005
Si6	0.46323	0.40615	0.62499	0.478005
Si7	0.96326	0.40612	0.12502	0.478005
Si8	0.96326	0.40616	0.62502	0.478005
Si9	0.28683	0.90613	0.12501	0.478005
Si10	0.28683	0.90613	0.62501	0.478005
Si11	0.78684	0.90616	0.125	0.478005
Si12	0.78684	0.90613	0.625	0.478005
Si13	0.21323	0.0939	0.87501	0.478005
Si14	0.21324	0.09388	0.375	0.478005
Si15	0.71328	0.09388	0.87502	0.478005
Si16	0.71325	0.09389	0.37501	0.478005
O1	0.36602	0.5917	0.87501	1.33137
O2	0.36601	0.59169	0.37501	1.33137
O3	0.86601	0.59169	0.875	1.33137
O4	0.86602	0.59169	0.375	1.33137
O5	0.13407	0.40836	0.12501	1.33137
O6	0.13406	0.40835	0.625	1.33137
O7	0.63406	0.40835	0.12501	1.33137
O8	0.63406	0.40834	0.62502	1.33137
O9	0.11601	0.90835	0.12501	1.33137
O10	0.11601	0.90834	0.62501	1.33137
O11	0.61601	0.90835	0.12501	1.33137
O12	0.61601	0.90834	0.62501	1.33137
O13	0.38411	0.09172	0.87499	1.33137
O14	0.38407	0.09169	0.37501	1.33137
O15	0.88409	0.09168	0.87501	1.33137
O16	0.88406	0.0917	0.37501	1.33137
O17	0.11083	0.44648	0.87503	1.33137
O18	0.11102	0.44601	0.37501	1.33137
O19	0.61103	0.44601	0.87501	1.33137
O20	0.61103	0.44601	0.37501	1.33137
O21	0.38905	0.55404	0.12501	1.33137
O22	0.38904	0.55403	0.62502	1.33137
O23	0.88905	0.55402	0.12501	1.33137
O24	0.88905	0.55402	0.62501	1.33137
O25	0.36103	0.05402	0.12501	1.33137
O26	0.36103	0.05402	0.625	1.33137
O27	0.86103	0.05403	0.12501	1.33137
O28	0.86104	0.05402	0.62501	1.33137
O29	0.13906	0.946	0.87501	1.33137
O30	0.13904	0.946	0.37501	1.33137
O31	0.63906	0.94599	0.87501	1.33137
O32	0.63905	0.94601	0.37501	1.33137
O33	0.11203	0.66335	0.98411	1.33137
O34	0.11204	0.66336	0.48412	1.33137
O35	0.61204	0.66336	0.98412	1.33137
O36	0.61203	0.66336	0.48411	1.33137
O37	0.38805	0.33667	0.23412	1.33137
O38	0.38803	0.33669	0.73411	1.33137
O39	0.88805	0.33667	0.2341	1.33137
O40	0.88805	0.33668	0.73412	1.33137
O41	0.36203	0.83666	0.0159	1.33137
O42	0.36202	0.83667	0.5159	1.33137
O43	0.86202	0.83667	0.0159	1.33137
O44	0.86204	0.83668	0.51591	1.33137
O45	0.13805	0.16336	0.7659	1.33137
O46	0.13804	0.16336	0.26589	1.33137
O47	0.63809	0.16334	0.76588	1.33137
O48	0.63805	0.16337	0.26589	1.33137
O49	0.38804	0.33668	0.01591	1.33137
O50	0.38804	0.33667	0.51591	1.33137
O51	0.88806	0.33667	0.0159	1.33137
O52	0.88804	0.33667	0.5159	1.33137
O53	0.11204	0.66336	0.7659	1.33137
O54	0.11203	0.66336	0.2659	1.33137
O55	0.61204	0.66336	0.7659	1.33137
O56	0.61203	0.66337	0.26589	1.33137
O57	0.13803	0.16337	0.98411	1.33137
O58	0.13805	0.16337	0.48412	1.33137
O59	0.63806	0.16336	0.98414	1.33137
O60	0.63804	0.16336	0.48412	1.33137
O61	0.36203	0.83667	0.23412	1.33137
O62	0.36204	0.83666	0.73412	1.33137
O63	0.86203	0.83668	0.23411	1.33137
O64	0.86205	0.83668	0.73412	1.33137

magnesium silicate (Mg2SiO4_CFO_USI_2121821137_Interstitial_O_0) top

Crystal data top

Mg₃₂O₆₅Si₁₆	α = 90°
M_r = 2267.05	β = 90°
Triclinic, P1	γ = 90°
Hall symbol: P 1	V = 1162.82 Å³
a = 9.5170 Å	Z = 1
b = 10.2042 Å	Melting point: not measured K
c = 11.9739 Å

Data collection top

h = →	l = →
k = →

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0.586950	0.323520	0.741370	0.008622
Mg2	0.586960	0.323530	0.241380	0.008622
Mg3	0.086970	0.323530	0.741380	0.008622
Mg4	0.086960	0.323520	0.241380	0.008622
Mg5	0.586950	0.323530	0.991380	0.008622
Mg6	0.586960	0.323530	0.491380	0.008622
Mg7	0.086970	0.323530	0.991380	0.008622
Mg8	0.086960	0.323530	0.491380	0.008622
Mg9	0.836960	0.823530	0.741380	0.008622
Mg10	0.836950	0.823520	0.241390	0.008622
Mg11	0.336950	0.823530	0.741380	0.008622
Mg12	0.336960	0.823530	0.241380	0.008622
Mg13	0.836950	0.823550	0.991370	0.008622
Mg14	0.836950	0.823520	0.491380	0.008622
Mg15	0.336950	0.823530	0.991380	0.008622
Mg16	0.336960	0.823530	0.491380	0.008622
Mg17	0.841160	0.100130	0.866380	0.008622
Mg18	0.841160	0.100120	0.366380	0.008622
Mg19	0.341160	0.100120	0.866380	0.008622
Mg20	0.341150	0.100120	0.366380	0.008622
Mg21	0.832760	0.546930	0.116380	0.008622
Mg22	0.832760	0.546930	0.616380	0.008622
Mg23	0.332770	0.546930	0.116380	0.008622
Mg24	0.332770	0.546930	0.616380	0.008622
Mg25	0.591160	0.046930	0.116370	0.008622
Mg26	0.591150	0.046930	0.616390	0.008622
Mg27	0.091150	0.046930	0.116380	0.008622
Mg28	0.091150	0.046930	0.616380	0.008622
Mg29	0.082760	0.600130	0.866380	0.008622
Mg30	0.082770	0.600130	0.366380	0.008622
Mg31	0.582760	0.600110	0.866380	0.008622
Mg32	0.582750	0.600130	0.366380	0.008622
Si1	0.623740	0.917390	0.866380	0.006169
Si2	0.623730	0.917390	0.366380	0.006169
Si3	0.123730	0.917380	0.866380	0.006169
Si4	0.123730	0.917390	0.366380	0.006169
Si5	0.050190	0.729660	0.116380	0.006169
Si6	0.050190	0.729670	0.616380	0.006169
Si7	0.550190	0.729660	0.116380	0.006169
Si8	0.550190	0.729670	0.616390	0.006169
Si9	0.873710	0.229660	0.116370	0.006169
Si10	0.873720	0.229660	0.616380	0.006169
Si11	0.373720	0.229670	0.116380	0.006169
Si12	0.373720	0.229670	0.616370	0.006169
Si13	0.800190	0.417390	0.866380	0.006169
Si14	0.800190	0.417390	0.366370	0.006169
Si15	0.300180	0.417390	0.866380	0.006169
Si16	0.300190	0.417400	0.366380	0.006169
O1	0.952900	0.915220	0.866380	0.016973
O2	0.952920	0.915210	0.366380	0.016973
O3	0.452930	0.915200	0.866380	0.016973
O4	0.452920	0.915210	0.366380	0.016973
O5	0.720990	0.731850	0.116380	0.016973
O6	0.720990	0.731850	0.616380	0.016973
O7	0.220990	0.731850	0.116380	0.016973
O8	0.220990	0.731850	0.616380	0.016973
O9	0.702930	0.231850	0.116380	0.016973
O10	0.702930	0.231850	0.616380	0.016973
O11	0.202930	0.231850	0.116380	0.016973
O12	0.202920	0.231850	0.616380	0.016973
O13	0.970990	0.415210	0.866380	0.016973
O14	0.970990	0.415210	0.366380	0.016973
O15	0.470980	0.415210	0.866380	0.016973
O16	0.470980	0.415200	0.366380	0.016973
O17	0.697920	0.769570	0.866380	0.016973
O18	0.697960	0.769520	0.366380	0.016973
O19	0.197970	0.769520	0.866380	0.016973
O20	0.197960	0.769520	0.366380	0.016973
O21	0.975940	0.877540	0.116370	0.016973
O22	0.975940	0.877540	0.616390	0.016973
O23	0.475950	0.877530	0.116380	0.016973
O24	0.475950	0.877530	0.616380	0.016973
O25	0.947960	0.377540	0.116380	0.016973
O26	0.947960	0.377540	0.616370	0.016973
O27	0.447960	0.377540	0.116380	0.016973
O28	0.447960	0.377540	0.616380	0.016973
O29	0.725950	0.269520	0.866380	0.016973
O30	0.725950	0.269530	0.366380	0.016973
O31	0.225950	0.269520	0.866380	0.016973
O32	0.225950	0.269530	0.366380	0.016973
O33	0.698910	0.986870	0.975500	0.016973
O34	0.698940	0.986880	0.475470	0.016973
O35	0.198940	0.986880	0.975480	0.016973
O36	0.198930	0.986880	0.475470	0.016973
O37	0.974980	0.660190	0.225470	0.016973
O38	0.974980	0.660180	0.725470	0.016973
O39	0.474980	0.660190	0.225470	0.016973
O40	0.474980	0.660180	0.725470	0.016973
O41	0.948950	0.160190	0.007290	0.016973
O42	0.948940	0.160190	0.507290	0.016973
O43	0.448940	0.160190	0.007290	0.016973
O44	0.448930	0.160180	0.507280	0.016973
O45	0.724980	0.486880	0.757280	0.016973
O46	0.724970	0.486880	0.257290	0.016973
O47	0.224970	0.486870	0.757280	0.016973
O48	0.224970	0.486880	0.257280	0.016973
O49	0.974970	0.660180	0.007290	0.016973
O50	0.974980	0.660180	0.507290	0.016973
O51	0.474980	0.660180	0.007280	0.016973
O52	0.474980	0.660190	0.507290	0.016973
O53	0.698940	0.986880	0.757280	0.016973
O54	0.698930	0.986880	0.257280	0.016973
O55	0.198940	0.986880	0.757290	0.016973
O56	0.198940	0.986880	0.257290	0.016973
O57	0.724980	0.486880	0.975480	0.016973
O58	0.724970	0.486880	0.475470	0.016973
O59	0.224970	0.486870	0.975480	0.016973
O60	0.224970	0.486880	0.475470	0.016973
O61	0.948940	0.160190	0.225470	0.016973
O62	0.948940	0.160180	0.725470	0.016973
O63	0.448930	0.160180	0.225470	0.016973
O64	0.448940	0.160190	0.725470	0.016973
O65	0.793560	0.000070	0.870670	0.016973

magnesium silicate (Mg2SiO4_CFO_USI_2121821137_Interstitial_Si_+4) top

Crystal data top

Mg₃₂O₆₄Si₁₇	α = 90°
M_r = 2279.18	β = 90°
Triclinic, P1	γ = 90°
Hall symbol: P 1	V = 1162.88 Å³
a = 9.5164 Å	Z = 1
b = 10.2043 Å	Melting point: not measured K
c = 11.9750 Å

Data collection top

h = →	l = →
k = →

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0.586960	0.460790	0.844830	0.008651
Mg2	0.586960	0.460810	0.344810	0.008651
Mg3	0.086970	0.460790	0.844840	0.008651
Mg4	0.086980	0.460780	0.344830	0.008651
Mg5	0.586960	0.460790	0.094830	0.008651
Mg6	0.586960	0.460760	0.594840	0.008651
Mg7	0.086960	0.460800	0.094830	0.008651
Mg8	0.086950	0.460780	0.594820	0.008651
Mg9	0.836960	0.960780	0.844820	0.008651
Mg10	0.836960	0.960790	0.344830	0.008651
Mg11	0.336970	0.960770	0.844820	0.008651
Mg12	0.336950	0.960780	0.344830	0.008651
Mg13	0.836940	0.960800	0.094790	0.008651
Mg14	0.836970	0.960780	0.594840	0.008651
Mg15	0.336970	0.960790	0.094830	0.008651
Mg16	0.336940	0.960800	0.594830	0.008651
Mg17	0.841170	0.237390	0.969840	0.008651
Mg18	0.841150	0.237330	0.469840	0.008651
Mg19	0.341150	0.237340	0.969830	0.008651
Mg20	0.341150	0.237330	0.469820	0.008651
Mg21	0.832740	0.684230	0.219820	0.008651
Mg22	0.832760	0.684250	0.719820	0.008651
Mg23	0.332770	0.684250	0.219820	0.008651
Mg24	0.332770	0.684250	0.719830	0.008651
Mg25	0.591160	0.184240	0.219840	0.008651
Mg26	0.591160	0.184220	0.719840	0.008651
Mg27	0.091170	0.184230	0.219810	0.008651
Mg28	0.091160	0.184240	0.719830	0.008651
Mg29	0.082750	0.737360	0.969820	0.008651
Mg30	0.082770	0.737330	0.469830	0.008651
Mg31	0.582790	0.737330	0.969830	0.008651
Mg32	0.582760	0.737340	0.469840	0.008651
Si1	0.623820	0.054660	0.969820	0.006304
Si2	0.623750	0.054650	0.469850	0.006304
Si3	0.123780	0.054650	0.969830	0.006304
Si4	0.123740	0.054660	0.469850	0.006304
Si5	0.050160	0.866910	0.219850	0.006304
Si6	0.050140	0.866930	0.719850	0.006304
Si7	0.550180	0.866910	0.219840	0.006304
Si8	0.550170	0.866940	0.719860	0.006304
Si9	0.873730	0.366900	0.219840	0.006304
Si10	0.873760	0.366920	0.719820	0.006304
Si11	0.373760	0.366910	0.219820	0.006304
Si12	0.373740	0.366900	0.719830	0.006304
Si13	0.800170	0.554630	0.969830	0.006304
Si14	0.800170	0.554660	0.469840	0.006304
Si15	0.300180	0.554690	0.969830	0.006304
Si16	0.300170	0.554660	0.469820	0.006304
O1	0.952870	0.052450	0.969810	0.017238
O2	0.952930	0.052450	0.469840	0.017238
O3	0.452930	0.052450	0.969820	0.017238
O4	0.452930	0.052460	0.469840	0.017238
O5	0.720980	0.869110	0.219810	0.017238
O6	0.720990	0.869110	0.719820	0.017238
O7	0.220990	0.869100	0.219820	0.017238
O8	0.220980	0.869120	0.719830	0.017238
O9	0.702940	0.369100	0.219840	0.017238
O10	0.702920	0.369120	0.719820	0.017238
O11	0.202930	0.369110	0.219820	0.017238
O12	0.202940	0.369110	0.719830	0.017238
O13	0.970980	0.552460	0.969830	0.017238
O14	0.970980	0.552460	0.469830	0.017238
O15	0.470980	0.552450	0.969830	0.017238
O16	0.470990	0.552460	0.469850	0.017238
O17	0.697900	0.906740	0.969850	0.017238
O18	0.697950	0.906780	0.469820	0.017238
O19	0.197970	0.906770	0.969830	0.017238
O20	0.197950	0.906770	0.469830	0.017238
O21	0.975970	0.014800	0.219820	0.017238
O22	0.975960	0.014800	0.719820	0.017238
O23	0.475970	0.014800	0.219830	0.017238
O24	0.475970	0.014790	0.719830	0.017238
O25	0.947940	0.514800	0.219830	0.017238
O26	0.947950	0.514790	0.719830	0.017238
O27	0.447930	0.514790	0.219830	0.017238
O28	0.447950	0.514800	0.719830	0.017238
O29	0.725960	0.406780	0.969830	0.017238
O30	0.725960	0.406780	0.469820	0.017238
O31	0.225960	0.406780	0.969830	0.017238
O32	0.225970	0.406780	0.469830	0.017238
O33	0.698960	0.124130	0.078930	0.017238
O34	0.698940	0.124140	0.578940	0.017238
O35	0.198960	0.124140	0.078940	0.017238
O36	0.198950	0.124140	0.578930	0.017238
O37	0.974950	0.797430	0.328930	0.017238
O38	0.974960	0.797430	0.828940	0.017238
O39	0.474950	0.797430	0.328930	0.017238
O40	0.474980	0.797440	0.828940	0.017238
O41	0.948970	0.297450	0.110720	0.017238
O42	0.948940	0.297440	0.610720	0.017238
O43	0.448950	0.297450	0.110720	0.017238
O44	0.448960	0.297430	0.610720	0.017238
O45	0.724950	0.624130	0.860710	0.017238
O46	0.724960	0.624140	0.360720	0.017238
O47	0.224960	0.624140	0.860720	0.017238
O48	0.224960	0.624140	0.360710	0.017238
O49	0.974960	0.797450	0.110710	0.017238
O50	0.974970	0.797440	0.610710	0.017238
O51	0.474960	0.797440	0.110720	0.017238
O52	0.474940	0.797440	0.610720	0.017238
O53	0.698990	0.124080	0.860740	0.017238
O54	0.698960	0.124130	0.360720	0.017238
O55	0.198970	0.124140	0.860720	0.017238
O56	0.198960	0.124120	0.360720	0.017238
O57	0.724950	0.624140	0.078940	0.017238
O58	0.724960	0.624140	0.578950	0.017238
O59	0.224950	0.624120	0.078940	0.017238
O60	0.224960	0.624140	0.578940	0.017238
O61	0.948960	0.297430	0.328930	0.017238
O62	0.948950	0.297420	0.828930	0.017238
O63	0.448950	0.297430	0.328940	0.017238
O64	0.448950	0.297440	0.828930	0.017238
Si17	0.793280	0.999990	0.922290	0.006304

magnesium silicate (Mg2SiO4_CFO_USI_2121821137_Vacancy_O_+2) top

Crystal data top

Mg₃₂O₆₃Si₁₆	α = 90°
M_r = 2235.09	β = 90°
Triclinic, P1	γ = 90°
Hall symbol: P 1	V = 1162.85 Å³
a = 9.5166 Å	Z = 1
b = 10.2044 Å	Melting point: not measured K
c = 11.9744 Å

Data collection top

h = →	l = →
k = →

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0.776230	0.336670	0.531960	0.008665
Mg2	0.776230	0.336660	0.031950	0.008665
Mg3	0.276240	0.336660	0.531950	0.008665
Mg4	0.276240	0.336650	0.031950	0.008665
Mg5	0.776220	0.336670	0.781960	0.008665
Mg6	0.776240	0.336660	0.281960	0.008665
Mg7	0.276240	0.336650	0.781960	0.008665
Mg8	0.276230	0.336650	0.281940	0.008665
Mg9	0.026230	0.836650	0.531940	0.008665
Mg10	0.026230	0.836650	0.031960	0.008665
Mg11	0.526230	0.836670	0.531960	0.008665
Mg12	0.526230	0.836670	0.031950	0.008665
Mg13	0.026240	0.836630	0.781950	0.008665
Mg14	0.026230	0.836650	0.281960	0.008665
Mg15	0.526220	0.836650	0.781950	0.008665
Mg16	0.526230	0.836660	0.281960	0.008665
Mg17	0.030460	0.113270	0.656930	0.008665
Mg18	0.030420	0.113230	0.156960	0.008665
Mg19	0.530420	0.113230	0.656940	0.008665
Mg20	0.530440	0.113230	0.156960	0.008665
Mg21	0.022030	0.560080	0.906950	0.008665
Mg22	0.022040	0.560090	0.406950	0.008665
Mg23	0.522040	0.560080	0.906950	0.008665
Mg24	0.522030	0.560070	0.406950	0.008665
Mg25	0.780440	0.060080	0.906950	0.008665
Mg26	0.780430	0.060090	0.406960	0.008665
Mg27	0.280430	0.060090	0.906950	0.008665
Mg28	0.280430	0.060090	0.406950	0.008665
Mg29	0.272030	0.613230	0.656950	0.008665
Mg30	0.272040	0.613230	0.156960	0.008665
Mg31	0.772030	0.613240	0.656950	0.008665
Mg32	0.772030	0.613240	0.156950	0.008665
Si1	0.813000	0.930530	0.656940	0.006257
Si2	0.813000	0.930530	0.156950	0.006257
Si3	0.312990	0.930530	0.656950	0.006257
Si4	0.313000	0.930530	0.156950	0.006257
Si5	0.239470	0.742800	0.906950	0.006257
Si6	0.239480	0.742790	0.406950	0.006257
Si7	0.739450	0.742770	0.906960	0.006257
Si8	0.739460	0.742790	0.406960	0.006257
Si9	0.063010	0.242810	0.906960	0.006257
Si10	0.063000	0.242790	0.406960	0.006257
Si11	0.562990	0.242790	0.906950	0.006257
Si12	0.562990	0.242780	0.406950	0.006257
Si13	0.989460	0.430530	0.656950	0.006257
Si14	0.989460	0.430540	0.156960	0.006257
Si15	0.489460	0.430520	0.656950	0.006257
Si16	0.489460	0.430510	0.156950	0.006257
O1	0.142200	0.928340	0.656950	0.016280
O2	0.142210	0.928340	0.156950	0.016280
O3	0.642210	0.928340	0.656960	0.016280
O4	0.642200	0.928340	0.156950	0.016280
O5	0.910250	0.745000	0.906950	0.016280
O6	0.910260	0.744990	0.406950	0.016280
O7	0.410260	0.744980	0.906950	0.016280
O8	0.410260	0.744990	0.406950	0.016280
O9	0.892200	0.244980	0.906950	0.016280
O10	0.892200	0.244980	0.406950	0.016280
O11	0.392200	0.244990	0.906950	0.016280
O12	0.392200	0.244980	0.406950	0.016280
O13	0.160250	0.428330	0.656950	0.016280
O14	0.160260	0.428330	0.156940	0.016280
O15	0.660250	0.428330	0.656950	0.016280
O16	0.660260	0.428330	0.156950	0.016280
O17	0.887090	0.782840	0.656980	0.016280
O18	0.887230	0.782650	0.156950	0.016280
O19	0.387230	0.782650	0.656950	0.016280
O20	0.387230	0.782650	0.156950	0.016280
O21	0.165230	0.890670	0.906960	0.016280
O22	0.165230	0.890660	0.406950	0.016280
O23	0.665240	0.890670	0.906950	0.016280
O24	0.665230	0.890670	0.406950	0.016280
O25	0.137220	0.390680	0.906950	0.016280
O26	0.137230	0.390670	0.406950	0.016280
O27	0.637240	0.390680	0.906950	0.016280
O28	0.637220	0.390670	0.406950	0.016280
O29	0.915220	0.282640	0.656960	0.016280
O30	0.915230	0.282650	0.156950	0.016280
O31	0.415230	0.282650	0.656950	0.016280
O32	0.415230	0.282640	0.156950	0.016280
O33	0.888220	0.000010	0.266060	0.016280
O34	0.388220	0.000010	0.766060	0.016280
O35	0.388220	0.000010	0.266060	0.016280
O36	0.164240	0.673300	0.016060	0.016280
O37	0.164240	0.673300	0.516060	0.016280
O38	0.664230	0.673310	0.016060	0.016280
O39	0.664230	0.673310	0.516060	0.016280
O40	0.138220	0.173300	0.797840	0.016280
O41	0.138220	0.173310	0.297850	0.016280
O42	0.638220	0.173300	0.797840	0.016280
O43	0.638220	0.173310	0.297850	0.016280
O44	0.914240	0.500010	0.547850	0.016280
O45	0.914250	0.500010	0.047850	0.016280
O46	0.414250	0.500010	0.547850	0.016280
O47	0.414240	0.500010	0.047850	0.016280
O48	0.164230	0.673310	0.797850	0.016280
O49	0.164240	0.673310	0.297860	0.016280
O50	0.664240	0.673310	0.797850	0.016280
O51	0.664240	0.673320	0.297850	0.016280
O52	0.888220	0.000010	0.547860	0.016280
O53	0.888220	0.000010	0.047860	0.016280
O54	0.388220	0.000010	0.547850	0.016280
O55	0.388220	0.000010	0.047850	0.016280
O56	0.914240	0.500010	0.766060	0.016280
O57	0.914250	0.500010	0.266060	0.016280
O58	0.414250	0.500010	0.766060	0.016280
O59	0.414240	0.500010	0.266060	0.016280
O60	0.138220	0.173310	0.016060	0.016280
O61	0.138220	0.173310	0.516060	0.016280
O62	0.638220	0.173310	0.016060	0.016280
O63	0.638220	0.173310	0.516060	0.016280

magnesium silicate (Mg2SiO4_CFO_USI_2121821137) top

Crystal data top

Mg₂O₄Si	V = 290.31 (6) Å³
M_r = 140.69	Z = 4
Orthorhombic, Pbnm	D_x = 3.219 Mg m⁻³
Hall symbol: -P 2c 2ab	Melting point: not measured K
a = 4.7542 (5) Å	Cu Kα radiation
b = 10.2048 (13) Å	T = 295 K
c = 5.9839 (7) Å

Data collection top

Bruker D8 Discover diffractometer	LynxEye-XET monochromator
Radiation source: fine-focus sealed tube	2θ_min = 5.000°, 2θ_max = 85.006°, 2θ_step = 0.015°

Refinement top

R_wp = 0.157	586 data points
R(F) = 0.414	(Δ/σ)_max = 0.0001

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0	0	0	0.90 (11)
Mg2	0.0147 (13)	0.2768 (4)	0.75	0.90 (11)
Si1	0.0701 (9)	0.4010 (4)	0.25	0.80 (11)
O1	0.2461 (15)	0.0854 (9)	0.75	1.00 (15)
O2	0.2809 (15)	0.0488 (11)	0.25	1.00 (15)
O3	0.2222 (11)	0.3459 (6)	0.4440 (10)	1.00 (15)

Geometric parameters (Å, º) top

Si1—O3	1.479 (6)

O3—Si1—O3	103.5 (3)

magnesium silicate (Mg2SiO4_HFO_USI_2121821138) top

Crystal data top

Mg₂O₄Si	V = 290.05 (2) Å³
M_r = 140.69	Z = 4
Orthorhombic, Pbnm	D_x = 3.222 Mg m⁻³
Hall symbol: -P 2c 2ab	Melting point: not measured K
a = 4.7523 (2) Å	Cu Kα radiation
b = 10.2027 (4) Å	T = 295 K
c = 5.9821 (2) Å

Data collection top

Bruker D8 Discover diffractometer	LynxEye-XET monochromator
Radiation source: fine-focus sealed tube	2θ_min = 5.000°, 2θ_max = 85.006°, 2θ_step = 0.015°

Refinement top

R_wp = 0.168	1142 data points
R(F) = 0.546	(Δ/σ)_max = 0.0001

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0	0	0	1.10 (8)
Mg2	0.0079 (7)	0.2770 (3)	0.75	1.10 (9)
Si1	0.0724 (5)	0.4048 (3)	0.25	0.90 (7)
O1	0.2414 (9)	0.0897 (5)	0.75	1.30 (17)
O2	0.2840 (9)	0.0459 (7)	0.25	1.30 (16)
O3	0.2167 (7)	0.3427 (4)	0.4535 (6)	1.30 (12)

Geometric parameters (Å, º) top

Si1—O3	1.534 (4)

O3—Si1—O3	105.03 (19)

magnesium silicate (Mg2SiO4_PFO_USI_2121821136) top

Crystal data top

Mg₂O₄Si	V = 290.39 (1) Å³
M_r = 140.69	Z = 4
Orthorhombic, Pbnm	D_x = 3.218 Mg m⁻³
Hall symbol: -P 2c 2ab	Melting point: not measured K
a = 4.7530 (1) Å	Cu Kα radiation
b = 10.2084 (2) Å	T = 295 K
c = 5.9848 (1) Å

Data collection top

Bruker D8 Discover diffractometer	LynxEye-XET monochromator
Radiation source: fine-focus sealed tube	2θ_min = 5.000°, 2θ_max = 85.006°, 2θ_step = 0.015°

Refinement top

R_wp = 0.114	2486 data points
R(F) = 0.159	(Δ/σ)_max = 0.0001

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0	0	0	0.95 (4)
Mg2	0.9929 (4)	0.27775 (16)	0.25	0.95 (4)
Si1	0.4268 (3)	0.09397 (16)	0.25	0.76 (4)
O1	0.7622 (5)	0.0923 (3)	0.25	0.54 (5)
O2	0.2202 (5)	0.4501 (4)	0.25	0.54 (5)
O3	0.2803 (4)	0.1621 (2)	0.0358 (4)	0.54 (5)

Geometric parameters (Å, º) top

Si1—O3	1.616 (2)

O3—Si1—O3	104.97 (12)

magnesium silicate (Mg2SiO4_RFO_USI_2121821033) top

Crystal data top

Mg₂O₄Si	V = 290.45 (1) Å³
M_r = 140.69	Z = 4
Orthorhombic, Pbnm	D_x = 3.218 Mg m⁻³
Hall symbol: -P 2c 2ab	Melting point: not measured K
a = 4.7515 (1) Å	Cu Kα radiation
b = 10.2127 (2) Å	T = 295 K
c = 5.9854 (1) Å

Data collection top

Bruker D8 Discover diffractometer	LynxEye-XET monochromator
Radiation source: fine-focus sealed tube	2θ_min = 5.000°, 2θ_max = 85.006°, 2θ_step = 0.015°

Refinement top

R_wp = 0.111	3022 data points
R(F) = 0.222	(Δ/σ)_max = 0.0001

Fractional atomic coordinates and isotropic or equivalent isotropic displacement parameters (Å²) top

	x	y	z	B_iso*/B_eq
Mg1	0	0	0	0.86 (4)
Mg2	0.0081 (4)	0.27743 (15)	0.75	0.86 (4)
Si1	0.0730 (3)	0.40599 (15)	0.25	0.60 (4)
O1	0.2364 (5)	0.0920 (3)	0.75	0.80 (5)
O2	0.2803 (5)	0.0507 (4)	0.25	0.80 (5)
O3	0.2203 (4)	0.3382 (2)	0.4646 (3)	0.80 (5)

Geometric parameters (Å, º) top

Si1—O3	1.618 (2)

O3—Si1—O3	105.06 (9)

Acknowledgements

We acknowledge Professor Dr Lucio Colombi Ciacchi, University of Bremen, and Dr Sokseiha Muy, EPFL Switzerland, for fruitful discussions on the project. Parts of this research were carried out at PETRA III and we would like to thank Dr Alexander Schökel for assistance in using the P02.1 Powder Diffraction and Total Scattering Beamline.

Conflict of interest

The authors hereby state no conflict of interest.

Funding information

We acknowledge support by the state of Bremen within the `Humans on Mars' initiative for APF `Materials on demand' (grant No. S1P3). We acknowledge DESY (Hamburg, Germany), a member of the Helmholtz Association HGF, for the provision of experimental facilities. AK acknowledges the Danish Research Council for covering travel expenses in relation to the synchrotron experiment (DanScatt) and the Deutsche Forschungsgemeinschaft (DFG, German science foundation) for funding of the project (grant Nos. KI2427/1-1 awarded to AK; 429360100). The authors gratefully acknowledge support from the DFG under Germany's Excellence Strategy (EXC 2077 grant No. 390741603, University Allowance, University of Bremen), as well as computing time granted by the Resource Allocation Board and provided on the supercomputers Lise and Emmy at NHR@ZIB and NHR@Göttingen as part of the NHR infrastructure. The calculations for this research were conducted with computing resources under the project hbi00059. NM acknowledges support by the National Center of Competence in Research, Materials' Revolution: Computational Design and Discovery of Novel Materials (MARVEL), funded by the Swiss National Science Foundation (grant No. 205602 awarded to NM).

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IUCrJ

Volume 11| Part 6| November 2024| Pages 977-990

ISSN: 2052-2525

https://doi.org/10.1107/S2052252524009722

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research papers\(\def\hfill{\hskip 5em}\def\hfil{\hskip 3em}\def\eqno#1{\hfil {#1}}\)

Synthesis, structural and spectroscopic characterization of defect-rich forsterite as a representative phase of Martian regolith

1. Introduction

2. Materials and methods

2.1. Synthesis of defect-poor forsterite

2.1.1. Reverse strike co-precipitation synthesis

2.1.2. Ball milling synthesis

2.2. Synthesis of defect-rich and healed forsterite

2.3. X-ray powder diffraction

2.4. Raman spectroscopy

2.5. Theoretical Raman calculations

2.6. X-ray synchrotron total scattering

2.7. DFT–PDF refinement

2.8. Energy calculations

3. Results and discussion

3.1. Synthesis

3.2. X-ray powder diffraction

3.3. Raman spectroscopy

3.4. PDF analysis

3.5. DFT–PDF refinement

3.5.1. Single-phase refinement

3.5.2. Stability of defective structure candidates

3.5.3. Multi-phase refinement

4. Conclusions and outlook

Supporting information

Acknowledgements

Conflict of interest

Funding information

References

research papers