Synthesis and crystal structure of a mixed alkaline-earth powellite, Ca0.84Sr0.16MoO4

Kissinger, R.M.; Chong, S.; Riley, B.J.; Crum, J.V.

doi:10.1107/S2056989019017092

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ISSN: 2056-9890

Volume 76| Part 2| February 2020| Pages 121-124

https://doi.org/10.1107/S2056989019017092

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Synthesis and crystal structure of a mixed alkaline-earth powellite, Ca_0.84Sr_0.16MoO₄

Ryan M. Kissinger,^a Saehwa Chong,^a ^* Brian J. Riley ^a and Jarrod V. Crum ^a

^aPacific Northwest National Laboratory, Richland, WA 99354, USA
^*Correspondence e-mail: saehwa.chong@pnnl.gov

Edited by A. Van der Lee, Université de Montpellier II, France (Received 16 December 2019; accepted 20 December 2019; online 3 January 2020)

A mixed alkaline-earth powellite, Ca_0.84Sr_0.16MoO₄ (calcium strontium molybdate), was synthesized by a flux method and its crystal structure was solved using single-crystal X-ray diffraction (SC-XRD) data. The compound crystallized in the I4₁/a space group as with a typical CaMoO₄ powellite, but with larger unit-cell parameters and unit-cell volume as a result of the partial incorporation of larger Sr cations into the Ca sites within the crystal. The unit cell and volume were well fitted with the trendline calculated from literature values, and the powder X-ray diffraction (P-XRD) pattern of the ground crystal is in good agreement with the calculated pattern from the solved structure.

Keywords: powellite; mixed alkaline-earth powellite; single-crystal XRD.

CCDC reference: 1973412

1. Chemical context

Powellite (CaMoO₄) is a naturally occurring mineral with the scheelite (CaWO₄) structure and has been studied for different applications including laser materials, phosphors, catalysts, electrodes, and radionuclide waste forms (Kato et al., 2005 ; Lei & Yan, 2008 ; Rabuffetti et al., 2014 ; Peterson et al., 2018 ; Ryu et al., 2007 ). Powellites doped with rare-earth elements have broad absorption bands and fluorescence emissions in the visible to near-infrared range (Kim & Kang, 2007 ; Lei & Yan, 2008; Schmidt et al., 2013 ), and isostructural BaMoO₄ and SrMoO₄ crystals have high photoluminescence emission in the visible spectral region (Bi et al., 2008 ; Lei et al., 2010 ). Powellite has been investigated for use in a potential electrode with Li cyclability for battery applications (Reddy et al., 2013 ). Alkaline-earth powellites crystallize during the development of the ceramic-waste forms for radionuclides in the high-level waste (HLW) raffinate stream from aqueous reprocessing of used nuclear fuel (Crum et al., 2019 ; Peterson et al., 2018).

Various methods have been used to synthesize scheelite-structured crystals including vapor diffusion sol-gel (VDSG), hydrothermal, molten salt reaction, Pechini, sonochemical, precipitation, solid-state, and pulsed-laser-induced methods (Culver et al., 2013 ; Lei & Yan, 2008; Wang et al., 2006 ; Kodaira et al., 2003 ; Geng et al., 2006 ; Ahmad et al., 2006 ; Ryu et al., 2007). The sizes and morphologies of the scheelite-structured crystals are important for specific applications and were controlled under some of these methods. Culver et al. (2013) successfully synthesized < 30 nm AMoO₄ (A = Ca, Sr, Ba) crystals using the VDSG method for Li-ion battery electrodes. Lei & Yan (2008) showed different sizes (30–40 nm) of CaMO₄:RE (M = W, Mo; RE = Eu, Tb) by varying the synthesis temperature (120–220°C) of hydrothermal experiments. Geng et al. (2006) used a sonochemical method with varying pH to synthesize PbWO₄ with different morphologies. Ryu et al. (2007) used the pulsed-laser ablation method to synthesize spherical powellite particles of 16–29 nm.

2. Structural commentary

Powellite crystallizes in the tetragonal space group I4₁/a and contains Ca²⁺ cations coordinated by eight [MoO₄]²⁻ tetrahedra, sharing an oxygen atom with each tetrahedron. The crystal structure of Ca_0.84Sr_0.16MoO₄ is isostructural to powellite, but with larger unit-cell parameters and (Ca/Sr)—O bond distances compared to CaMoO₄ powellite because of the partial incorporation of the larger Sr²⁺ cation into the Ca²⁺ sites (Fig. 1). Similarly, the Ba—O and Sr—O bond distances in BaMoO₄ (Nassif et al., 1999 ; Panchal et al., 2006 ; Cavalcante et al., 2008 ) and SrMoO₄ (Egorov-Tismenko et al., 1967 ; Gürmen et al., 1971 ; Nogueira et al., 2013 ) are longer than the Ca—O bond distance in CaMoO₄ (Aleksandrov et al., 1968 ; Gürmen et al., 1971) or the (Ca/Sr)—O bond distance in this study. Fig. 2 shows a summary of unit-cell parameters (a and c), unit-cell volumes (V), and unit-cell densities (ρ) from the literature as well as the current composition including CaMoO₄ (Aleksandrov et al., 1968; Gürmen et al., 1971; Wandahl & Christensen, 1987 ; Peterson et al., 2018), Ca_0.747Sr_0.194Ba_0.059MoO₄ (Peterson et al., 2018), SrMoO₄ (Gürmen et al., 1971; Egorov-Tismenko et al., 1967; Nogueira et al., 2013; Peterson et al., 2018), Sr_0.81Ba_0.19MoO₄ (Nogueira et al., 2013), Sr_0.59Ba_0.41MoO₄ (Nogueira et al., 2013), Ca_0.088Sr_0.256Ba_0.656MoO₄ (Peterson et al., 2018), Sr_0.27Ba_0.73MoO₄ (Nogueira et al., 2013), and BaMoO₄ (Cavalcante et al., 2008; Panchal et al., 2006; Vegard & Refsum, 1927 ; Nogueira et al., 2013; Nassif et al., 1999; Bylichkina et al., 1970 ; Peterson et al., 2018). The structural parameters of Ca_0.84Sr_0.16MoO₄ fit well to the trendlines in Fig. 2, and the data show well-fit linear relationships for the unit cell and volume. For the density, a non-linear trendline was drawn based on the densities of end members, and a linear trendline was drawn using the densities from both end members and mixed powellites from the literature (Fig. 2d). Despite our expectation, the density values did not fit well into either trendline, and more density values from different chemistries of mixed alkaline-earth powellites would help to understand the behavior of densities in powellites. The trendlines show that the unit cells, volumes, and densities all increase with larger alkaline-earth cations. Details of unit cell parameters, volumes, and densities from literature and the current study are summarized in Table 1.

Table 1
Summary of data on (Ca, Sr, Ba)MoO₄ crystals from the literature and current study

Densities are calculated from crystallographic data.

Chemistry	a (Å)	c (Å)	Volume (Å³)	Density (Mg m⁻³)	Reference
CaMoO₄	5.224	11.43	311.93	4.26	(Aleksandrov et al., 1968)
CaMoO₄	5.224	11.43	312.17	4.26	(Gürmen et al., 1971)
CaMoO₄	5.2235	11.4298	311.86	4.26	(Wandahl & Christensen, 1987)
CaMoO₄	5.2268	11.4345	312.38	4.25	(Peterson et al., 2018)
Ca_0.84Sr_0.16MoO₄	5.2592	11.5500	319.45	4.32	Current study
SrMoO₄	5.394	12.017	349.64	4.7	(Egorov-Tismenko et al., 1967)
SrMoO₄	5.3944	12.02	349.78	4.7	(Gürmen et al., 1971)
SrMoO₄	5.4026	12.0411	351.46	4.68	(Nogueira et al., 2013)
SrMoO₄	5.3963	12.0248	350.16	4.7	(Peterson et al., 2018)
Sr_0.81Ba_0.19MoO₄	5.4571	12.2548	364.95	4.68	(Nogueira et al., 2013)
Sr_0.59Ba_0.41MoO₄	5.5073	12.4789	378.49	4.7	(Nogueira et al., 2013)
Sr_0.27Ba_0.73MoO₄	5.5491	12.6680	390.08	4.83	(Nogueira et al., 2013)
BaMoO₄	5.567	12.78	396.07	4.99	(Vegard & Refsum, 1927)
BaMoO₄	5.62	12.82	404.91	4.88	(Bylichkina et al., 1970)
BaMoO₄	5.5479	12.743	392.22	5.03	(Nassif et al., 1999)
BaMoO₄	5.5800	12.820	399.17	4.95	(Panchal et al., 2006)
BaMoO₄	5.5696	12.7865	396.64	4.98	(Cavalcante et al., 2008)
BaMoO₄	5.5848	12.8292	400.15	4.93	(Nogueira et al., 2013)
BaMoO₄	5.5828	12.8204	399.59	4.94	(Peterson et al., 2018)

Figure 1
(a) Crystal structure of Ca_0.84Sr_0.16MoO₄ and (b) coordination of eight [MoO₄]²⁻ tetrahedra with respect to the Ca/Sr cations.

Figure 2
Summary of (a) unit-cell parameter a, (b) unit-cell parameter c, (c) unit-cell volume (V), and (d) density (ρ) as a function of the average ionic crystal radii in the structure (coordination number = 8) from Shannon (1976

). Data for the end members include averages and standard deviations from multiple sources.

3. Synthesis and crystallization

The mixed alkaline-earth powellite, Ca_0.84Sr_0.16MoO₄, was synthesized using the end-member powellites within a LiCl flux. The loss of mass due to dehydration for LiCl was measured by placing a given amount of LiCl (Alfa Aesar, >99%) into a furnace at 100°C and weighing daily for five days. For the synthesis of CaMoO₄ and SrMoO₄, the stoichiometric amounts of CaCO₃ (Alfa Aesar, >99.5%), SrCO₃ (Sigma Aldrich, >99.9%), and MoO₃ (Alfa Aesar, >99.5%) were placed in Pt/10%Rh crucible and heated to 1500°C at 5°C min⁻¹, held for 30 min, ramped down to 1400°C at 1°C min⁻¹, held for 1 h, and then cooled down to room temperature at 1°C min⁻¹. Details of synthesis are provided elsewhere (Peterson et al., 2018). For the synthesis of Ca_0.84Sr_0.16MoO₄, appropriate amounts of CaMoO₄ and SrMoO₄ powders were used as precursors and mixed together in Pt/10%Rh crucibles. Then, LiCl was added at a 1:1 ratio by mass, where the mass of CaMoO₄ + SrMoO₄ was equivalent to that of the LiCl. The crucible was covered with a tight-fitting Pt/10%Rh lid and heated according to a method described by Arora et al. (1983 ). The furnace was ramped up to 850°C, held for 2 h, abruptly decreased to 750°C, cooled to 550°C at a rate of 3°C h⁻¹, and then the furnace was shut off. Crystals were recovered after washing in a sonic bath and rinsing with deionized water.

4. Refinement

Crystal data, data collection and structure refinement details are summarized in Table 2. For the occupancy refinement of the Ca and Sr sites, the occupancy parameters of both Sr and Ca were refined with isotropic atomic displacement parameters while keeping the total occupancy as 1. The refined occupancy values were 0.86 for Ca and 0.14 for Sr after rounding, and then these values were fixed and anisotropic refinements were performed on all the atoms including Ca, Sr, Mo, and O. The final refinement converged at R₁ = 4.30%, and the goodness-of-fit was 1.44. The single crystals of Ca_0.84Sr_0.16MoO₄ were ground with a mortar and pestle. A selected crystal for SC-XRD was placed on a cryoloop in oil (Parabar 10312, Hampton Research). Powder X-ray diffraction (P-XRD) was performed using a Bruker D8 Advance diffractometer on a zero-background quartz sample holder. The measured P-XRD pattern was compared to the calculated pattern from the solved structure, and they were in good agreement (see Fig. 3).

Table 2
Experimental details

Crystal data
Chemical formula	Ca_0.84Sr_0.16MoO₄
M_r	207.6
Crystal system, space group	Tetragonal, I4₁/a
Temperature (K)	293
a, c (Å)	5.2592 (1), 11.5497 (4)
V (Å³)	319.46 (1)
Z	4
Radiation type	Mo Kα
μ (mm⁻¹)	7.92
Crystal size (mm)	0.05 × 0.05 × 0.03

Data collection
Diffractometer	Bruker D8 QUEST CMOS area detector
Absorption correction	Multi-scan (SADABS)
T_min, T_max	0.628, 0.747
No. of measured, independent and observed [I > 2σ(I)] reflections	6597, 396, 238
R_int	0.131

Refinement
R[F > 3σ(F)], wR(F), S	0.043, 0.042, 1.44
No. of reflections	396
No. of parameters	14
Δρ_max, Δρ_min (e Å⁻³)	2.76, −2.57
Computer programs: APEX3 and SAINT (Bruker, 2012 ), JANA2006 (Petříček et al., 2014 ), SUPERFLIP (Palatinus & Chapuis, 2007 ), VESTA (Momma & Izumi, 2011 ), publCIF (Westrip, 2010 ).

Figure 3
Comparison between P-XRD pattern of ground Ca_0.84Sr_0.16MoO₄ single crystals and calculated pattern generated from the solved structure.

Supporting information

CCDC reference: 1973412

Crystal structure: contains datablocks global, I. DOI: https://doi.org/10.1107/S2056989019017092/vn2156sup1.cif

Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019017092/vn2156Isup2.hkl

checkCIF report

Computing details top

Data collection: APEX3 (Bruker, 2012); cell refinement: JANA2006 (Petříček et al., 2014); data reduction: SAINT (Bruker, 2012); program(s) used to solve structure: SUPERFLIP (Palatinus & Chapuis, 2007); program(s) used to refine structure: JANA2006 (Petříček et al., 2014); molecular graphics: VESTA (Momma & Izumi, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).

Calcium strontium molybdate top

Crystal data top

Ca_0.84Sr_0.16MoO₄	D_x = 4.317 Mg m⁻³
M_r = 207.6	Mo Kα radiation, λ = 0.71069 Å
Tetragonal, I4₁/a:1	Cell parameters from 6597 reflections
Hall symbol: I 4bw -1bw	θ = 4.3–36.5°
a = 5.2592 (1) Å	µ = 7.92 mm⁻¹
c = 11.5497 (4) Å	T = 293 K
V = 319.46 (1) Å³	Irregular, light white
Z = 4	0.05 × 0.05 × 0.03 mm
F(000) = 388

Data collection top

Bruker D8 QUEST CMOS area detector diffractometer	238 reflections with I > 2σ(I)
Radiation source: X-ray tube	R_int = 0.131
φ and ω scans	θ_max = 36.5°, θ_min = 4.3°
Absorption correction: multi-scan (SADABS)	h = −8→8
T_min = 0.628, T_max = 0.747	k = −8→8
6597 measured reflections	l = −19→19
396 independent reflections

Refinement top

Refinement on F	2 constraints
R[F > 3σ(F)] = 0.043	Primary atom site location: iterative
wR(F) = 0.042	Weighting scheme based on measured s.u.'s w = 1/(σ²(F) + 0.0001F²)
S = 1.44	(Δ/σ)_max = 0.024
396 reflections	Δρ_max = 2.76 e Å⁻³
14 parameters	Δρ_min = −2.57 e Å⁻³
0 restraints

Special details top

Refinement. F000 reported from JANA is 388.0 and calculated is 387.5 from CheckCIF.Both occupancies of Ca and Sr were refined with isotropic ADP while keeping the total occupancy at 1 and same position for both atoms, and their occupancy values were closed to 0.84 ±0.001 and 0.16±0.001 respectively between the refinements. Therefore, we fixed the occupancy to 0.84 and 0.16 with rounding off, and the anisotropic refinement was applied after fixing the occupancies.The difference in reported and caculated rho(max)is likely due to difference in how PLATON and JANA2006 calculate Fourier maps and take weights of reflections into Fourier calculations.

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

	x	y	z	U_iso*/U_eq	Occ. (<1)
Mo1	0.5	0.5	0	0.00778 (13)
Ca1	1	0.5	0.25	0.0074 (2)	0.84
Sr1	1	0.5	0.25	0.0074 (2)	0.16
O1	0.7420 (7)	0.6444 (7)	0.0837 (3)	0.0114 (8)

Atomic displacement parameters (Å²) top

	U¹¹	U²²	U³³	U¹²	U¹³	U²³
Mo1	0.0067 (2)	0.0067 (2)	0.0100 (2)	0	0	0
Ca1	0.0076 (4)	0.0076 (4)	0.0072 (4)	0	0	0
Sr1	0.0076 (4)	0.0076 (4)	0.0072 (4)	0	0	0
O1	0.0127 (17)	0.0088 (16)	0.0126 (10)	−0.0017 (14)	−0.0039 (12)	0.0016 (11)

Geometric parameters (Å, º) top

Mo1—Sr1ⁱ	3.7188	Ca1—Sr1ⁱⁱⁱ	3.9054
Mo1—Sr1ⁱⁱ	3.7188	Ca1—Sr1^iv	3.9054
Mo1—Sr1ⁱⁱⁱ	3.7188	Sr1—Sr1^viii	3.9054
Mo1—Sr1^iv	3.7188	Sr1—Sr1^ix	3.9054
Mo1—O1	1.769 (3)	Sr1—Sr1ⁱⁱⁱ	3.9054
Mo1—O1^v	1.769 (3)	Sr1—Sr1^iv	3.9054
Mo1—O1^vi	1.769 (3)	Sr1—O1	2.471 (3)
Mo1—O1^vii	1.769 (3)	Sr1—O1^x	2.471 (3)
Ca1—Ca1^viii	3.9054	Sr1—O1^ix	2.505 (4)
Ca1—Ca1^ix	3.9054	Sr1—O1^xi	2.505 (4)
Ca1—Ca1ⁱⁱⁱ	3.9054	Sr1—O1^xii	2.505 (4)
Ca1—Ca1^iv	3.9054	Sr1—O1^xiii	2.505 (4)
Ca1—Sr1	0	Sr1—O1^xiv	2.471 (3)
Ca1—Sr1^viii	3.9054	Sr1—O1^xv	2.471 (3)
Ca1—Sr1^ix	3.9054

Sr1ⁱ—Mo1—Sr1ⁱⁱ	90	Ca1—Sr1—Ca1^ix	0
Sr1ⁱ—Mo1—Sr1ⁱⁱⁱ	90	Ca1—Sr1—Ca1ⁱⁱⁱ	0
Sr1ⁱ—Mo1—Sr1^iv	180.0 (5)	Ca1—Sr1—Ca1^iv	0
Sr1ⁱ—Mo1—O1	144.30 (11)	Ca1—Sr1—Sr1^viii	0
Sr1ⁱ—Mo1—O1^v	35.70 (11)	Ca1—Sr1—Sr1^ix	0
Sr1ⁱ—Mo1—O1^vi	78.16 (12)	Ca1—Sr1—Sr1ⁱⁱⁱ	0
Sr1ⁱ—Mo1—O1^vii	101.84 (12)	Ca1—Sr1—Sr1^iv	0
Sr1ⁱⁱ—Mo1—Sr1ⁱⁱⁱ	180.0 (5)	Ca1—Sr1—O1	0
Sr1ⁱⁱ—Mo1—Sr1^iv	90	Ca1—Sr1—O1^x	0
Sr1ⁱⁱ—Mo1—O1	101.84 (12)	Ca1—Sr1—O1^ix	0
Sr1ⁱⁱ—Mo1—O1^v	78.16 (12)	Ca1—Sr1—O1^xi	0
Sr1ⁱⁱ—Mo1—O1^vi	144.30 (11)	Ca1—Sr1—O1^xii	0
Sr1ⁱⁱ—Mo1—O1^vii	35.70 (11)	Ca1—Sr1—O1^xiii	0
Sr1ⁱⁱⁱ—Mo1—Sr1^iv	90	Ca1—Sr1—O1^xiv	0
Sr1ⁱⁱⁱ—Mo1—O1	78.16 (12)	Ca1—Sr1—O1^xv	0
Sr1ⁱⁱⁱ—Mo1—O1^v	101.84 (12)	Ca1^viii—Sr1—Ca1^ix	84.65
Sr1ⁱⁱⁱ—Mo1—O1^vi	35.70 (11)	Ca1^viii—Sr1—Ca1ⁱⁱⁱ	123.14
Sr1ⁱⁱⁱ—Mo1—O1^vii	144.30 (11)	Ca1^viii—Sr1—Ca1^iv	123.14
Sr1^iv—Mo1—O1	35.70 (11)	Ca1^viii—Sr1—Sr1^viii	0.0 (5)
Sr1^iv—Mo1—O1^v	144.30 (11)	Ca1^viii—Sr1—Sr1^ix	84.65
Sr1^iv—Mo1—O1^vi	101.84 (12)	Ca1^viii—Sr1—Sr1ⁱⁱⁱ	123.14
Sr1^iv—Mo1—O1^vii	78.16 (12)	Ca1^viii—Sr1—Sr1^iv	123.14
O1—Mo1—O1^v	113.77 (15)	Ca1^viii—Sr1—O1	101.82 (8)
O1—Mo1—O1^vi	107.37 (16)	Ca1^viii—Sr1—O1^x	160.80 (8)
O1—Mo1—O1^vii	107.37 (16)	Ca1^viii—Sr1—O1^ix	102.56 (7)
O1^v—Mo1—O1^vi	107.37 (16)	Ca1^viii—Sr1—O1^xi	37.99 (8)
O1^v—Mo1—O1^vii	107.37 (16)	Ca1^viii—Sr1—O1^xii	130.55 (8)
O1^vi—Mo1—O1^vii	113.77 (15)	Ca1^viii—Sr1—O1^xiii	85.44 (8)
Ca1^viii—Ca1—Ca1^ix	84.65	Ca1^viii—Sr1—O1^xiv	68.42 (8)
Ca1^viii—Ca1—Ca1ⁱⁱⁱ	123.14	Ca1^viii—Sr1—O1^xv	38.60 (8)
Ca1^viii—Ca1—Ca1^iv	123.14	Ca1^ix—Sr1—Ca1ⁱⁱⁱ	123.14
Ca1^viii—Ca1—Sr1	0	Ca1^ix—Sr1—Ca1^iv	123.14
Ca1^viii—Ca1—Sr1^viii	0.0 (5)	Ca1^ix—Sr1—Sr1^viii	84.65
Ca1^viii—Ca1—Sr1^ix	84.65	Ca1^ix—Sr1—Sr1^ix	0.0 (5)
Ca1^viii—Ca1—Sr1ⁱⁱⁱ	123.14	Ca1^ix—Sr1—Sr1ⁱⁱⁱ	123.14
Ca1^viii—Ca1—Sr1^iv	123.14	Ca1^ix—Sr1—Sr1^iv	123.14
Ca1^ix—Ca1—Ca1ⁱⁱⁱ	123.14	Ca1^ix—Sr1—O1	160.80 (8)
Ca1^ix—Ca1—Ca1^iv	123.14	Ca1^ix—Sr1—O1^x	101.82 (8)
Ca1^ix—Ca1—Sr1	0	Ca1^ix—Sr1—O1^ix	37.99 (8)
Ca1^ix—Ca1—Sr1^viii	84.65	Ca1^ix—Sr1—O1^xi	102.56 (7)
Ca1^ix—Ca1—Sr1^ix	0.0 (5)	Ca1^ix—Sr1—O1^xii	85.44 (8)
Ca1^ix—Ca1—Sr1ⁱⁱⁱ	123.14	Ca1^ix—Sr1—O1^xiii	130.55 (8)
Ca1^ix—Ca1—Sr1^iv	123.14	Ca1^ix—Sr1—O1^xiv	38.60 (8)
Ca1ⁱⁱⁱ—Ca1—Ca1^iv	84.65	Ca1^ix—Sr1—O1^xv	68.42 (8)
Ca1ⁱⁱⁱ—Ca1—Sr1	0	Ca1ⁱⁱⁱ—Sr1—Ca1^iv	84.65
Ca1ⁱⁱⁱ—Ca1—Sr1^viii	123.14	Ca1ⁱⁱⁱ—Sr1—Sr1^viii	123.14
Ca1ⁱⁱⁱ—Ca1—Sr1^ix	123.14	Ca1ⁱⁱⁱ—Sr1—Sr1^ix	123.14
Ca1ⁱⁱⁱ—Ca1—Sr1ⁱⁱⁱ	0.0 (5)	Ca1ⁱⁱⁱ—Sr1—Sr1ⁱⁱⁱ	0.0 (5)
Ca1ⁱⁱⁱ—Ca1—Sr1^iv	84.65	Ca1ⁱⁱⁱ—Sr1—Sr1^iv	84.65
Ca1^iv—Ca1—Sr1	0	Ca1ⁱⁱⁱ—Sr1—O1	68.42 (8)
Ca1^iv—Ca1—Sr1^viii	123.14	Ca1ⁱⁱⁱ—Sr1—O1^x	38.60 (8)
Ca1^iv—Ca1—Sr1^ix	123.14	Ca1ⁱⁱⁱ—Sr1—O1^ix	85.44 (8)
Ca1^iv—Ca1—Sr1ⁱⁱⁱ	84.65	Ca1ⁱⁱⁱ—Sr1—O1^xi	130.55 (8)
Ca1^iv—Ca1—Sr1^iv	0.0 (5)	Ca1ⁱⁱⁱ—Sr1—O1^xii	102.56 (7)
Sr1—Ca1—Sr1^viii	0	Ca1ⁱⁱⁱ—Sr1—O1^xiii	37.99 (8)
Sr1—Ca1—Sr1^ix	0	Ca1ⁱⁱⁱ—Sr1—O1^xiv	160.80 (8)
Sr1—Ca1—Sr1ⁱⁱⁱ	0	Ca1ⁱⁱⁱ—Sr1—O1^xv	101.82 (8)
Sr1—Ca1—Sr1^iv	0	Ca1^iv—Sr1—Sr1^viii	123.14
Sr1^viii—Ca1—Sr1^ix	84.65	Ca1^iv—Sr1—Sr1^ix	123.14
Sr1^viii—Ca1—Sr1ⁱⁱⁱ	123.14	Ca1^iv—Sr1—Sr1ⁱⁱⁱ	84.65
Sr1^viii—Ca1—Sr1^iv	123.14	Ca1^iv—Sr1—Sr1^iv	0.0 (5)
Sr1^ix—Ca1—Sr1ⁱⁱⁱ	123.14	Ca1^iv—Sr1—O1	38.60 (8)
Sr1^ix—Ca1—Sr1^iv	123.14	Ca1^iv—Sr1—O1^x	68.42 (8)
Sr1ⁱⁱⁱ—Ca1—Sr1^iv	84.65	Ca1^iv—Sr1—O1^ix	130.55 (8)
Mo1^viii—Sr1—Mo1^xvi	90	Ca1^iv—Sr1—O1^xi	85.44 (8)
Mo1^viii—Sr1—Mo1^ix	90	Ca1^iv—Sr1—O1^xii	37.99 (8)
Mo1^viii—Sr1—Mo1^xvii	180.0 (5)	Ca1^iv—Sr1—O1^xiii	102.56 (7)
Mo1^viii—Sr1—Ca1	0	Ca1^iv—Sr1—O1^xiv	101.82 (8)
Mo1^viii—Sr1—Ca1^viii	61.57	Ca1^iv—Sr1—O1^xv	160.80 (8)
Mo1^viii—Sr1—Ca1^ix	118.43	Sr1^viii—Sr1—Sr1^ix	84.65
Mo1^viii—Sr1—Ca1ⁱⁱⁱ	61.57	Sr1^viii—Sr1—Sr1ⁱⁱⁱ	123.14
Mo1^viii—Sr1—Ca1^iv	118.43	Sr1^viii—Sr1—Sr1^iv	123.14
Mo1^viii—Sr1—Sr1^viii	61.57	Sr1^viii—Sr1—O1	101.82 (8)
Mo1^viii—Sr1—Sr1^ix	118.43	Sr1^viii—Sr1—O1^x	160.80 (8)
Mo1^viii—Sr1—Sr1ⁱⁱⁱ	61.57	Sr1^viii—Sr1—O1^ix	102.56 (7)
Mo1^viii—Sr1—Sr1^iv	118.43	Sr1^viii—Sr1—O1^xi	37.99 (8)
Mo1^viii—Sr1—O1	80.15 (8)	Sr1^viii—Sr1—O1^xii	130.55 (8)
Mo1^viii—Sr1—O1^x	99.85 (8)	Sr1^viii—Sr1—O1^xiii	85.44 (8)
Mo1^viii—Sr1—O1^ix	98.33 (8)	Sr1^viii—Sr1—O1^xiv	68.42 (8)
Mo1^viii—Sr1—O1^xi	81.67 (8)	Sr1^viii—Sr1—O1^xv	38.60 (8)
Mo1^viii—Sr1—O1^xii	155.66 (7)	Sr1^ix—Sr1—Sr1ⁱⁱⁱ	123.14
Mo1^viii—Sr1—O1^xiii	24.34 (7)	Sr1^ix—Sr1—Sr1^iv	123.14
Mo1^viii—Sr1—O1^xiv	127.27 (8)	Sr1^ix—Sr1—O1	160.80 (8)
Mo1^viii—Sr1—O1^xv	52.73 (8)	Sr1^ix—Sr1—O1^x	101.82 (8)
Mo1^xvi—Sr1—Mo1^ix	180.0 (5)	Sr1^ix—Sr1—O1^ix	37.99 (8)
Mo1^xvi—Sr1—Mo1^xvii	90	Sr1^ix—Sr1—O1^xi	102.56 (7)
Mo1^xvi—Sr1—Ca1	0	Sr1^ix—Sr1—O1^xii	85.44 (8)
Mo1^xvi—Sr1—Ca1^viii	61.57	Sr1^ix—Sr1—O1^xiii	130.55 (8)
Mo1^xvi—Sr1—Ca1^ix	118.43	Sr1^ix—Sr1—O1^xiv	38.60 (8)
Mo1^xvi—Sr1—Ca1ⁱⁱⁱ	118.43	Sr1^ix—Sr1—O1^xv	68.42 (8)
Mo1^xvi—Sr1—Ca1^iv	61.57	Sr1ⁱⁱⁱ—Sr1—Sr1^iv	84.65
Mo1^xvi—Sr1—Sr1^viii	61.57	Sr1ⁱⁱⁱ—Sr1—O1	68.42 (8)
Mo1^xvi—Sr1—Sr1^ix	118.43	Sr1ⁱⁱⁱ—Sr1—O1^x	38.60 (8)
Mo1^xvi—Sr1—Sr1ⁱⁱⁱ	118.43	Sr1ⁱⁱⁱ—Sr1—O1^ix	85.44 (8)
Mo1^xvi—Sr1—Sr1^iv	61.57	Sr1ⁱⁱⁱ—Sr1—O1^xi	130.55 (8)
Mo1^xvi—Sr1—O1	52.73 (8)	Sr1ⁱⁱⁱ—Sr1—O1^xii	102.56 (7)
Mo1^xvi—Sr1—O1^x	127.27 (8)	Sr1ⁱⁱⁱ—Sr1—O1^xiii	37.99 (8)
Mo1^xvi—Sr1—O1^ix	155.66 (7)	Sr1ⁱⁱⁱ—Sr1—O1^xiv	160.80 (8)
Mo1^xvi—Sr1—O1^xi	24.34 (7)	Sr1ⁱⁱⁱ—Sr1—O1^xv	101.82 (8)
Mo1^xvi—Sr1—O1^xii	81.67 (8)	Sr1^iv—Sr1—O1	38.60 (8)
Mo1^xvi—Sr1—O1^xiii	98.33 (8)	Sr1^iv—Sr1—O1^x	68.42 (8)
Mo1^xvi—Sr1—O1^xiv	80.15 (8)	Sr1^iv—Sr1—O1^ix	130.55 (8)
Mo1^xvi—Sr1—O1^xv	99.85 (8)	Sr1^iv—Sr1—O1^xi	85.44 (8)
Mo1^ix—Sr1—Mo1^xvii	90	Sr1^iv—Sr1—O1^xii	37.99 (8)
Mo1^ix—Sr1—Ca1	0	Sr1^iv—Sr1—O1^xiii	102.56 (7)
Mo1^ix—Sr1—Ca1^viii	118.43	Sr1^iv—Sr1—O1^xiv	101.82 (8)
Mo1^ix—Sr1—Ca1^ix	61.57	Sr1^iv—Sr1—O1^xv	160.80 (8)
Mo1^ix—Sr1—Ca1ⁱⁱⁱ	61.57	O1—Sr1—O1^x	77.98 (11)
Mo1^ix—Sr1—Ca1^iv	118.43	O1—Sr1—O1^ix	151.21 (11)
Mo1^ix—Sr1—Sr1^viii	118.43	O1—Sr1—O1^xi	73.95 (11)
Mo1^ix—Sr1—Sr1^ix	61.57	O1—Sr1—O1^xii	76.60 (11)
Mo1^ix—Sr1—Sr1ⁱⁱⁱ	61.57	O1—Sr1—O1^xiii	68.41 (11)
Mo1^ix—Sr1—Sr1^iv	118.43	O1—Sr1—O1^xiv	127.16 (12)
Mo1^ix—Sr1—O1	127.27 (8)	O1—Sr1—O1^xv	127.16 (12)
Mo1^ix—Sr1—O1^x	52.73 (8)	O1^x—Sr1—O1^ix	73.95 (11)
Mo1^ix—Sr1—O1^ix	24.34 (7)	O1^x—Sr1—O1^xi	151.21 (11)
Mo1^ix—Sr1—O1^xi	155.66 (7)	O1^x—Sr1—O1^xii	68.41 (11)
Mo1^ix—Sr1—O1^xii	98.33 (8)	O1^x—Sr1—O1^xiii	76.60 (11)
Mo1^ix—Sr1—O1^xiii	81.67 (8)	O1^x—Sr1—O1^xiv	127.16 (12)
Mo1^ix—Sr1—O1^xiv	99.85 (8)	O1^x—Sr1—O1^xv	127.16 (12)
Mo1^ix—Sr1—O1^xv	80.15 (8)	O1^ix—Sr1—O1^xi	134.61 (10)
Mo1^xvii—Sr1—Ca1	0	O1^ix—Sr1—O1^xii	98.56 (12)
Mo1^xvii—Sr1—Ca1^viii	118.43	O1^ix—Sr1—O1^xiii	98.56 (12)
Mo1^xvii—Sr1—Ca1^ix	61.57	O1^ix—Sr1—O1^xiv	76.60 (11)
Mo1^xvii—Sr1—Ca1ⁱⁱⁱ	118.43	O1^ix—Sr1—O1^xv	68.41 (11)
Mo1^xvii—Sr1—Ca1^iv	61.57	O1^xi—Sr1—O1^xii	98.56 (12)
Mo1^xvii—Sr1—Sr1^viii	118.43	O1^xi—Sr1—O1^xiii	98.56 (12)
Mo1^xvii—Sr1—Sr1^ix	61.57	O1^xi—Sr1—O1^xiv	68.41 (11)
Mo1^xvii—Sr1—Sr1ⁱⁱⁱ	118.43	O1^xi—Sr1—O1^xv	76.60 (11)
Mo1^xvii—Sr1—Sr1^iv	61.57	O1^xii—Sr1—O1^xiii	134.61 (10)
Mo1^xvii—Sr1—O1	99.85 (8)	O1^xii—Sr1—O1^xiv	73.95 (11)
Mo1^xvii—Sr1—O1^x	80.15 (8)	O1^xii—Sr1—O1^xv	151.21 (11)
Mo1^xvii—Sr1—O1^ix	81.67 (8)	O1^xiii—Sr1—O1^xiv	151.21 (11)
Mo1^xvii—Sr1—O1^xi	98.33 (8)	O1^xiii—Sr1—O1^xv	73.95 (11)
Mo1^xvii—Sr1—O1^xii	24.34 (7)	O1^xiv—Sr1—O1^xv	77.98 (11)
Mo1^xvii—Sr1—O1^xiii	155.66 (7)	Mo1—O1—Sr1	133.45 (18)
Mo1^xvii—Sr1—O1^xiv	52.73 (8)	Mo1—O1—Sr1^iv	119.96 (15)
Mo1^xvii—Sr1—O1^xv	127.27 (8)	Sr1—O1—Sr1^iv	103.40 (13)
Ca1—Sr1—Ca1^viii	0

Symmetry codes: (i) −y+1/2, x−1, z−1/4; (ii) −y+1/2, x, z−1/4; (iii) −y+3/2, x−1, z−1/4; (iv) −y+3/2, x, z−1/4; (v) −x+1, −y+1, z; (vi) y, −x+1, −z; (vii) −y+1, x, −z; (viii) −y+1, x−1/2, z+1/4; (ix) −y+2, x−1/2, z+1/4; (x) −x+2, −y+1, z; (xi) y, −x+3/2, z+1/4; (xii) −x+2, −y+3/2, −z+1/4; (xiii) x, y−1/2, −z+1/4; (xiv) y+1/2, −x+3/2, −z+1/2; (xv) −y+3/2, x−1/2, −z+1/2; (xvi) −y+1, x+1/2, z+1/4; (xvii) −y+2, x+1/2, z+1/4.

Summary of data on (Ca, Sr, Ba)MoO4 crystals from the literature and current study. top

Densities are calculated from crystallographic data.

Chemistry	a (Å)	c (Å)	Volume (Å³)	Density (Mg m^-3)	Reference
CaMoO₄	5.224	11.43	311.93	4.26	(Aleksandrov et al., 1968)
CaMoO₄	5.224	11.43	312.17	4.26	(Gürmen et al., 1971)
CaMoO₄	5.2235	11.4298	311.86	4.26	(Wandahl & Christensen, 1987)
CaMoO₄	5.2268	11.4345	312.38	4.25	(Peterson et al., 2018)
Ca_0.84Sr_0.16MoO₄	5.2592	11.5500	319.45	4.32	Current study
SrMoO₄	5.394	12.017	349.64	4.7	(Egorov-Tismenko et al., 1967)
SrMoO₄	5.3944	12.02	349.78	4.7	(Gürmen et al., 1971)
SrMoO₄	5.4026	12.0411	351.46	4.68	(Nogueira et al., 2013)
SrMoO₄	5.3963	12.0248	350.16	4.7	(Peterson et al., 2018)
Sr_0.81Ba_0.19MoO₄	5.4571	12.2548	364.95	4.68	(Nogueira et al., 2013)
Sr_0.59Ba_0.41MoO₄	5.5073	12.4789	378.49	4.7	(Nogueira et al., 2013)
Sr_0.27Ba_0.73MoO₄	5.5491	12.6680	390.08	4.83	(Nogueira et al., 2013)
BaMoO₄	5.567	12.78	396.07	4.99	(Vegard & Refsum, 1927)
BaMoO₄	5.62	12.82	404.91	4.88	(Bylichkina et al., 1970)
BaMoO₄	5.5479	12.743	392.22	5.03	(Nassif et al., 1999)
BaMoO₄	5.5800	12.820	399.17	4.95	(Panchal et al., 2006)
BaMoO₄	5.5696	12.7865	396.64	4.98	(Cavalcante et al., 2008)
BaMoO₄	5.5848	12.8292	400.15	4.93	(Nogueira et al., 2013)
BaMoO₄	5.5828	12.8204	399.59	4.94	(Peterson et al., 2018)

Acknowledgements

The authors acknowledge financial support from the US Department of Energy Office of Nuclear Energy (DOE-NE). The Pacific Northwest National Laboratory is operated by Battelle under Contract Number DE-AC05–76RL01830.

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