research communications
Synthesis and 3BSi2O10
of a neodymium borosilicate, NdaPacific Northwest National Laboratory, Richland, WA 99352, USA
*Correspondence e-mail: jarrod.crum@pnnl.gov
A lanthanide borosilicate, trineodymium borosilicate or Nd3BSi2O10, was synthesized using a method with LiCl, and its structure was determined from X-ray powder diffraction (XRD) and (EPMA). The structure is composed of layers with [SiO4]4− and [BSiO6]5− anions alternating along the c axis linked by Nd3+ cations between them.
Keywords: LiCl flux; neodymium borosilicate; lanthanum borosilicate; glass-ceramic waste form; powder diffraction.
CCDC reference: 1909612
1. Chemical context
Lanthanide borosilicates (i.e. Ln3BSi2O10) crystallize as one of the major phases within the residual glass matrix in some formulations of the glass-ceramic waste form for treatment of raffinate high-level waste (Crum et al., 2012, 2014, 2016). Studies on the crystal chemistry and crystallization mechanism of lanthanide borosilicates are important in understanding the formation and durability of crystalline phases in the glass-ceramic waste forms (Crum et al., 2012, 2014, 2016). In this work, we report the synthesis method and of Nd3BSi2O10 solved by powder XRD and EPMA analysis.
Different compositions of lanthanide borosilicates including LnBSiO5 (Ln = La, Ce, Pr, Nd, Sm; McAndrew & Scott, 1955; Neumann et al., 1966; Nekrasov & Nekrasova, 1971; Voronkov & Pyatenko, 1967; Burns et al., 1993; Chi et al., 1997; Shi et al., 1997), Ln5Si2BO13 (Ln = La, Eu, Gd, Dy; Mazza et al., 2000; Yuan et al., 2007; Naidu et al., 2010), and Ln3BSi2O10 (Ln = La, Ce, Pr, Nd, Sm, Eu, Gd, Tb; Chi et al., 1996a,b; Müller-Bunz & Schleid, 1998; Chi et al., 1998, Shvanskii et al., 2000; Müller-Bunz et al., 2001; Bräuchle & Huppertz, 2015) have been reported in the literature. LnBSiO5 has the stillwellite structure containing single or mixed lanthanide cations with infinite helical chains composed of six-membered rings formed by two [BO4]5− and one [SiO4]4− tetrahedral units (Chi et al., 1997; Burns et al., 1993; Voronkov & Pyatenko, 1967; Shi et al., 1997). Ln5Si2BO13 has an apatite-like structure in which the non-tetrahedral cation sites are occupied by trivalent rare-earth cations, and B and Si occupy the same tetrahedral site (Mazza et al., 2000). Ln3BSi2O10 contains layers with [SiO4]4− and [BSiO6]5− anions alternating along the c axis linked by trivalent cations between them, and Nd3BSi2O10 in this work is isostructural to previously reported Ln3BSi2O10 compounds (Chi et al., 1996a,b, 1998, Braeuchle & Huppertz, 2015; Shvanskii et al., 2000; Müller–Bunz et al., 2001).
2. Structural commentary
The [BSiO6]5− anion in Nd3BSi2O10 is formed by [Si1O4]4− and [BO3]3− anions sharing an oxygen atom, with an average <Si1—O> distance of 1.613 Å and an average <B—O> distance of 1.466 Å (Fig. 1a), while the [Si2O4]4− ion has an average <Si2—O> distance of 1.590 Å. The [BSi1O6]5− and [Si2O4]4− anions are arranged alternately along the c axis (Fig. 2). The Nd cations occupy the interlayer sites between the anion units. Nd1 and Nd3 are coordinated by eight oxygen atoms with average <Nd1—O> and <Nd3—O> distances of 2.477 and 2.520 Å, respectively, and Nd2 is coordinated by nine oxygen atoms with an average <Nd2—O> distance of 2.575 Å (Fig. 1b). In our previous paper (Kroll et al., 2019), we summarized the crystallographic data from the literature on other Ln3BSi2O10 chemistries (Braeuchle & Huppertz, 2015; Chi et al., 1996a,b, 1998; Müller–Bunz et al., 2001; Shvanskii et al., 2000) as a function of the ionic crystal radii (rc) for the VIII-coordinated Ln3+ constituent according to Shannon (1976) to create predictive models for the unit-cell parameters (i.e., a, b, and c), cell volume, and cell density. The measured values of a (9.7889 Å), b (7.1077 Å), c (23.0893 Å), cell volume (1606.5 Å3), and density (5.4551 Mg m−3) all fit reasonably well with the values calculated using the rc for Nd (1.109 Å), i.e., a (9.799 Å), b (7.111 Å), c (23.095 Å), cell volume (1608.4 Å3), and cell density (5.49 Mg/m3). Detailed atomic coordinates, bond lengths, and angles are given in Tables S1 and S2 in the supporting information.
3. Synthesis and crystallization
Nd3BSi2O10 was synthesized by a LiCl method; more details are provided elsewhere (Kroll et al., 2019). Powdered B2O3 was placed into a Pt–10%Rh crucible, melted at 1273 K in air to dehydrate fully and quenched on an Inconel plate. Appropriate amounts of Nd2O3, SiO2, and B2O3 were mixed in an agate mortar and pestle. LiCl was dried at 378 K for several hours and mixed with oxides in a 1:1 ratio by mass in a DiamoniteTM mortar and pestle. Mixed powder was placed into a fused quartz tube, covered with a quartz lid, heated to 1173 K at 5 K min−1, held for 24 h at 1173 K, and then cooled down to room temperature at 1 K min−1. The Nd3BSi2O10 was recovered from the LiCl through vacuum filtration with several rinsing steps using deionized water and a Büchner funnel. The recovered heat-treated powder was ground finer in the mortar and pestle and pressed into a 20 mm diameter pellet using a cold press with 110 MPa. The pellet was sintered at 1373 K. The heating condition included ramping up at 2 K min−1 to 1373 K, dwelling for 4 h, and cooling to room temperature at 2 K min−1. The heat-treated pellet, which was blue–violet in color, was ground for XRD and EPMA. Two EPMA measurements were performed on the sample to verify the composition of the crystal and showed that it closely matches the calculated value (Fig. 3).
4. Refinement
Crystal data, data collection and structure . A Rietveld plot is shown in Fig. 4. The structure of Nd3BSi2O10 was determined using on the initial model with a similar chemistry and structure using TOPAS (version 4.2; Bruker, 2009). Based on the fitting of peak positions and profile of experimental XRD patterns to a reference pattern, Ce3BSi2O10 (ICSD 94423) was used as a starting model. The Ce atoms in ICSD 94423 were replaced with Nd atoms, and all the atomic positions for Nd, B, Si, and O were refined. The profile of the model was refined from 14.5° to avoid a hump around 13.5° in the fitting of the background resulting from an instrumental artifact. The displacement parameters (Beq) were not refined and fixed to 1 Å2 to avoid divergence and unreasonable error values. In addition, parameters for scale factors, microstructure effects, and with spherical harmonic function (Järvinen, 1993) were refined, and the background was fitted with a Chebychev polynomial.
details are summarized in Table 1Supporting information
CCDC reference: 1909612
https://doi.org/10.1107/S2056989019005024/vn2146sup1.cif
contains datablocks global, I. DOI:Structure factors: contains datablock I. DOI: https://doi.org/10.1107/S2056989019005024/vn2146Isup2.hkl
https://doi.org/10.1107/S2056989019005024/vn2146sup3.docx
details and tables for atomic positions,bond length, and angles. DOI:Rietveld powder data: contains datablock I. DOI: https://doi.org/10.1107/S2056989019005024/vn2146Isup4.rtv
TOPAS inp file about https://doi.org/10.1107/S2056989019005024/vn2146sup5.docx
DOI:Data collection: XRD Commander (Kienle et al., 2003); cell
TOPAS (Bruker, 2009); program(s) used to solve structure: TOPAS (Bruker, 2009); program(s) used to refine structure: TOPAS (Bruker, 2009); molecular graphics: VESTA (Momma & Izumi, 2011); software used to prepare material for publication: publCIF (Westrip, 2010).Nd3BSi2O10 | Z = 8 |
Mr = 659.7 | Dx = 5.455 Mg m−3 |
Orthorhombic, Pbca | Cu Kα radiation, λ = 1.54188 Å |
a = 9.78891 (17) Å | T = 295 K |
b = 7.10774 (12) Å | blue_violet |
c = 23.0893 (4) Å | flat_sheet, 25 × 25 mm |
V = 1606.49 (5) Å3 |
Bruker D8 Advance diffractometer | Data collection mode: reflection |
Radiation source: sealed X-ray tube | Scan method: step |
Specimen mounting: packed powder pellet | 2θmin = 14.5°, 2θmax = 90°, 2θstep = 0.014° |
Rp = 0.03 | 82 parameters |
Rwp = 0.04 | Weighting scheme based on measured s.u.'s |
Rexp = 0.011 | (Δ/σ)max = 0.011 |
RBragg = 0.013 | Background function: Chebychev |
5738 data points | Preferred orientation correction: spherical harmonic |
Profile function: pseudo-Voigt |
Refinement. background fitted from 14.5 degree to avoid a hump from instrumental artifact |
x | y | z | Biso*/Beq | ||
Nd1 | 0.4909 (2) | 0.3621 (3) | 0.42810 (6) | 1 | |
Nd2 | 0.1338 (2) | 0.3296 (4) | 0.33652 (7) | 1 | |
Nd3 | 0.2655 (2) | 0.0934 (3) | 0.18257 (7) | 1 | |
B1 | 0.249 (4) | 0.387 (7) | 0.9703 (13) | 1 | |
Si1 | 0.3810 (10) | 0.3516 (16) | 0.0787 (3) | 1 | |
Si2 | 0.4381 (9) | 0.3240 (17) | 0.2814 (4) | 1 | |
O1 | 0.2558 (17) | 0.254 (3) | 0.9191 (7) | 1 | |
O2 | 0.1165 (18) | 0.399 (3) | 0.9903 (7) | 1 | |
O3 | 0.3697 (19) | 0.348 (3) | 0.0088 (6) | 1 | |
O4 | 0.4525 (17) | 0.170 (3) | 0.1055 (7) | 1 | |
O5 | 0.2286 (15) | 0.346 (3) | 0.1083 (7) | 1 | |
O6 | 0.4662 (17) | 0.537 (3) | 0.0938 (8) | 1 | |
O7 | 0.6028 (18) | 0.293 (2) | 0.2773 (7) | 1 | |
O8 | 0.4151 (15) | 0.369 (2) | 0.2120 (7) | 1 | |
O9 | 0.3903 (18) | 0.466 (2) | 0.3239 (7) | 1 | |
O10 | 0.3481 (15) | 0.138 (3) | 0.2880 (6) | 1 |
Nd1—O1i | 2.454 (17) | Nd3—O7vi | 2.325 (16) |
Nd1—O2ii | 2.460 (19) | B1—O2 | 1.38 (4) |
Nd1—O2iii | 2.265 (17) | Si1—O3 | 1.618 (16) |
Nd1—O4iv | 2.39 (2) | Si1—O4 | 1.59 (2) |
Nd1—O6v | 2.40 (2) | Si1—O5 | 1.641 (18) |
Nd2—O1i | 2.327 (17) | Si1—O6 | 1.60 (2) |
Nd2—O8vi | 2.432 (15) | Si2—O7 | 1.63 (2) |
Nd2—O10vii | 2.47 (2) | Si2—O8 | 1.649 (19) |
Nd3—Nd3viii | 3.567 (3) | Si2—O9 | 1.483 (19) |
Nd3—Nd3vii | 3.567 (3) | Si2—O10 | 1.60 (2) |
Nd3—O5viii | 2.457 (19) | ||
O1i—Nd1—O2ii | 83.2 (6) | O3—Si1—O6 | 105.4 (11) |
O1i—Nd1—O2iii | 128.2 (6) | O4—Si1—O5 | 102.6 (11) |
O1i—Nd1—O4iv | 119.9 (6) | O4—Si1—O6 | 110.7 (11) |
O1i—Nd1—O6v | 79.8 (6) | O5—Si1—O6 | 113.8 (11) |
O2ii—Nd1—O2iii | 70.5 (6) | O7—Si2—O8 | 96.0 (9) |
O2ii—Nd1—O4iv | 69.9 (6) | O7—Si2—O9 | 116.3 (11) |
O2ii—Nd1—O6v | 149.5 (6) | O7—Si2—O10 | 116.1 (11) |
O2iii—Nd1—O4iv | 92.2 (7) | O8—Si2—O9 | 117.9 (11) |
O2iii—Nd1—O6v | 101.0 (7) | O8—Si2—O10 | 100.3 (9) |
O4iv—Nd1—O6v | 140.6 (6) | O9—Si2—O10 | 109.0 (10) |
O1i—Nd2—O8vi | 149.1 (6) | Nd1ix—O1—Nd2ix | 117.7 (7) |
O1i—Nd2—O10vii | 124.2 (6) | Nd1x—O2—Nd1xi | 109.5 (7) |
O8vi—Nd2—O10vii | 75.6 (5) | Nd1x—O2—B1 | 104 (2) |
Nd3viii—Nd3—Nd3vii | 170.24 (8) | Nd1xi—O2—B1 | 141.4 (17) |
Nd3viii—Nd3—O5viii | 44.7 (4) | Nd1v—O4—Si1 | 135.9 (10) |
Nd3viii—Nd3—O7vi | 123.3 (4) | Nd3vii—O5—Si1 | 104.6 (9) |
Nd3vii—Nd3—O5viii | 135.7 (4) | Nd1iv—O6—Si1 | 147.0 (11) |
Nd3vii—Nd3—O7vi | 48.2 (4) | Nd3xii—O7—Si2 | 137.5 (9) |
O5viii—Nd3—O7vi | 137.0 (5) | Nd2xii—O8—Si2 | 107.8 (8) |
O3—Si1—O4 | 113.9 (11) | Nd2viii—O10—Si2 | 137.7 (9) |
O3—Si1—O5 | 110.7 (10) |
Symmetry codes: (i) x, −y+1/2, z−1/2; (ii) −x+1/2, −y+1, z−1/2; (iii) x+1/2, y, −z+3/2; (iv) −x+1, y+1/2, −z+1/2; (v) −x+1, y−1/2, −z+1/2; (vi) x−1/2, y, −z+1/2; (vii) −x+1/2, y+1/2, z; (viii) −x+1/2, y−1/2, z; (ix) x, −y+1/2, z+1/2; (x) −x+1/2, −y+1, z+1/2; (xi) x−1/2, y, −z+3/2; (xii) x+1/2, y, −z+1/2. |
Funding information
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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