Rietveld refinement of the low temperature crystal structures of Cs2XSi5O12 (X = Cu, Cd and Zn) European Journal of Chemistry 12 (1) (2021) 60-63 European Journal of Chemistry ISSN 2153-2249 (Print) / ISSN 2153-2257 (Online) – Copyright © 2021 The Authors – Atlanta Publishing House LLC – Printed in the USA. This work is published and licensed by Atlanta Publishing House LLC – CC BY NC – Some Rights Reserved. https://dx.doi.org/10.5155/eurjchem.12.1.60-63.2089 European Journal of Chemistry View Journal Online View Article Online Rietveld refinement of the low temperature crystal structures of Cs2XSi5O12 (X = Cu, Cd and Zn) Anthony Martin Thomas Bell * Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield, S1 1WB, United Kingdom anthony.bell@shu.ac.uk (A.M.T.B.) * Corresponding author at: Materials and Engineering Research Institute, Sheffield Hallam University, Sheffield, S1 1WB, United Kingdom. e-mail: anthony.bell@shu.ac.uk (A.M.T. Bell). 10.5155/eurjchem.12.1.60-63.2089 Received: 28 January 2021 Received in revised form: 17 February 2021 Accepted: 18 February 2021 Published online: 31 March 2021 Printed: 31 March 2021 The synthetic leucite silicate framework mineral analogues Cs2XSi5O12 (X = Cu, Cd, Zn) were prepared by high-temperature solid-state synthesis. The results of Rietveld refinement, using 18 keV synchrotron X-ray powder diffraction data collected at low temperatures (8K X = Cu, Zn; 10K X = Cd) show that the title compounds crystallize in the space group Pbca and are isostructural with the ambient temperature structures of these analogues. The structures consist of tetrahedrally coordinated SiO4 and XO4 sharing corners to form a partially substituted silicate framework. Extraframework Cs cations sit in channels in the framework. All atoms occupy the 8c general position for this space group. In these refined structures, silicon and X atoms are ordered onto separate tetrahedrally coordinated sites (T- sites). Cesium Rietveld refinement Solid-state structures Synchrotron radiation X-ray powder diffraction Silicate framework structure Cite this: Eur. J. Chem. 2021, 12(1), 60-63 Journal website: www.eurjchem.com 1. Introduction Anhydrous synthetic analogues of the silicate framework minerals leucite KAlSi2O6 [1] and pollucite CsAlSi2O6 [2] can be prepared with the general formulae ABSi2O6 and A2CSi5O12. A is an alkali metal cation (K, Rb, Cs), B is a trivalent cation (Al, B, Fe3+, Ga) and C is a divalent cation (Be, Mg, Mn, Fe2+, Co, Ni, Cu, Zn, Cd). These structures consist of a tetrahedrally coordinated silicate framework structure with B or C cations partially substituting for Si on the tetrahedrally coordinated silicon sites (T-sites). A cation sits in the extraframework channels, these extraframework cations can be removed by ion exchange which makes them of technological interest as possible storage media for radioactive Cs from nuclear waste [3]. Leucite analogues with high symmetry structures such as I41/a tetragonal KGaSi2O6 [4] and Ia-3d cubic Rb2ZnSi5O12 [5] have B and C cations disordered with Si over the T-sites. However, lower symmetry leucite structures are known where C cations and Si are ordered onto separate T-sites. The P21/c monoclinic K2MgSi5O12 [6] has 12 fully ordered T-sites, 10 of these are fully occupied by Si and 2 are fully occupied by Mg. Three more P21/c K2XSi5O12 structures [7] are known which are isostructural with K2MgSi5O12 and have fully ordered T-sites. The Pbca orthorhombic structure of Cs2CdSi5O12 [8] has 6 fully ordered T-sites, 5 of these are fully occupied by Si and 1 is fully occupied by Cd. Five more structures with the general formula Cs2XSi5O12 [9-11], four structures with the general formula Rb2XSi5O12 [9,10,12], and three structures with the general formula RbCsXSi5O12 [13] are all isostructural with the fully T- site cation ordered structure of Cs2CdSi5O12. However, NMR [14] and high-resolution synchrotron X-ray powder diffraction [10] studies on Cs2ZnSi5O12 described a Pbca structure where Zn is partially disordered over 2 of the 6 T-sites. A high temperature X-ray powder diffraction study on K2MgSi5O12 [15] showed a first-order phase transition from P21/c to Pbca. A high temperature study from 295-1173 K [16] has also been done on these three Cs2XSi5O12 (X = Cu, Cd, Zn) leucite analogues using lower resolution synchrotron X-ray powder diffraction. For X = Cd, the Pbca structure, with complete T-site cation ordering, is retained up to 1173 K. For X = Cu the Pbca structure is retained up to 1173 K, but there is a first-order transition to a less distorted structure with a larger unit-cell volume at ~333 K. For X = Zn the ambient temperature crystal structure shows (unlike for the high-resolution synchrotron X-ray powder diffraction study) that the Pbca structure is also isostructural with Cs2CdSi5O12 with complete T-site cation ordering. ABSTRACT RESEARCH ARTICLE KEYWORDS https://dx.doi.org/10.5155/eurjchem.12.1.60-63.2089 https://www.eurjchem.com/ https://dx.doi.org/10.5155/eurjchem.12.1.60-63.2089 mailto:anthony.bell@shu.ac.uk mailto:anthony.bell@shu.ac.uk http://www.eurjchem.com/ https://crossmark.crossref.org/dialog/?doi=10.5155/eurjchem.12.1.60-63.2089&domain=pdf&date_stamp=2021-03-31 Anthony Martin Thomas Bell / European Journal of Chemistry 12 (1) (2021) 60-63 61 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.1.60-63.2089 Table 1. Crystal data and details of the structure refinement for all low temperature leucite analogues. Ambient temperature lattice parameters are given for comparison. Parameters X = Cu X = Cd X = Zn Chemical formula Cs2CuO12Si5 Cs2CdO12Si5 Cs2ZnO12Si5 Formula weight 661.78 710.64 663.61 Temperature (K) 8 10 8 Crystal system Orthorhombic Orthorhombic Orthorhombic Space group Pbca Pbca Pbca a, (Å) 13.56321(14) 13.6760(3) 13.6356(7) b, (Å) 13.52837(14) 13.8008(4) 13.6440(11) c, (Å) 13.60617(14) 13.8666(4) 13.6358(10) Volume (Å3) 2496.57(5) 2617.17(12) 2536.9(3) Z 8 8 8 ρcalc (g/cm3) 3.52124(7) 3.6070(2) 3.4757(5) μ (mm-1) 54.23 53.78 55.96 Specimen shape, size (mm) Cylinder, 10 × 0.3 Cylinder, 10 × 0.3 Cylinder, 10 × 0.3 Radiation Synchrotron, λ = 0.687286 A� Synchrotron, λ = 0.688000 A� Synchrotron, λ = 0.688233 A� Diffractometer In-house design In-house design In-house design Specimen mounting Borosilicate glass capillary Borosilicate glass capillary Borosilicate glass capillary Data collection mode Transmission Transmission Transmission Scan method Step Step Step 2q values (°) 2θmin = 5.000 2θmax = 50.000 2θstep = 0.004 2θmin = 5.000 2θmax = 50.000 2θstep = 0.004 2θmin = 5.000 2θmax = 50.000 2θstep = 0.004 R-factors Rp = 4.575, Rwp = 5.968, Rexp = 1.470, RBragg = 13.734 Rp = 4.937, Rwp = 6.611, Rexp = 1.308, RBragg = 17.515 Rp = 4.226, Rwp = 5.311, Rexp = 1.371, RBragg = 16.500 Goodness-of-fit χ2 = 16.472 χ2 = 25.541 χ2 = 15.003 No. of parameters 74 73 73 No. of restraints 24 24 24 Ambient temperature Crystal system Orthorhombic Orthorhombic Orthorhombic Space group Pbca Pbca Pbca a, (Å) 13.58943(6) 13.6714(1) 13.6415(9) b, (Å) 13.57355(5) 13.8240(1) 13.6233(8) c, (Å) 13.62296(4) 13.8939(1) 13.6653(9) Volume (Å3) 2512.847(13) 2625.83(6) 2539.6(3) (a) (b) Figure 1. (a) The crystal structure of Cs2CuSi5O12 at 8 K. Turquoise spheres show Cs cations, blue polyhedra show SiO4 units, green polyhedra show CuO4 units and red spheres represent O atoms. (b) Rietveld difference plot for the single-phase refinement of Cs2CuSi5O12 from synchrotron X-ray powder diffraction data collected at 8 K. The red, blue and grey lines show respectively the observed, calculated and difference plots. Calculated Bragg reflection positions are indicated by green crosses. However, the sample with X = Zn shows evidence for a transition to a previously unknown Pa-3 cubic structure, with some T-site cation disorder, at 566 K on heating. This transition is reversible on cooling to 633 K. 2. Experimental 2.1. Sample preparation The samples were made from stoichiometric mixtures of Cs2CO3, SiO2, and CuO (X = Cu) or CdO (X = Cd) or ZnO (X = Zn). For X = Cu the sample was prepared by hydrothermal synthesis, the X = Cu and Zn samples were prepared by dry synthesis. The X = Cu [11], X = Cd [8] and X = Zn [9] sample mixtures were heated in platinum crucibles overnight at 873 K to decompose the carbonates. These mixtures were reground, returned to the crucibles and melted at 1473 K (X = Cu, Cd) or 1683 K (X = Zn) before quenching by dipping the bases of the crucible into water. The resultant X = Cu sample was sealed in a platinum capsule with 2% added water and heated in a cold-seal pressure vessel at 683 K, 500 bar pressure, for 6 days to produce a hydrothermally synthesised sample. The resultant X = Cd sample mixture was heated at ambient pressure in a platinum crucible at 1123 K for 5 days to produce a dry synthesised sample. The resultant X = Zn mixture was heated at ambient pressure in a platinum crucible at 1373 K for 4.5 days to produce another dry synthesised sample. Full synthetic details are given in [11, X = Cu; 8, X = Cd; 9, X = Zn]. 62 Anthony Martin Thomas Bell / European Journal of Chemistry 12 (1) (2021) 60-63 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.1.60-63.2089 (a) (b) Figure 2. (a) The crystal structure of Cs2CdSi5O12 at 10 K. Turquoise spheres show Cs cations, blue polyhedra show SiO4 units, purple polyhedra show CdO4 units and red spheres represent O atoms. (b) Rietveld difference plot for the single-phase refinement of Cs2CdSi5O12 from synchrotron X-ray powder diffraction data collected at 10 K. The red, blue and grey lines show respectively the observed, calculated and difference plots. Calculated Bragg reflection positions are indicated by green crosses. (a) (b) Figure 3. (a) The crystal structure of Cs2ZnSi5O12 at 8 K. Turquoise spheres show Cs cations, blue polyhedra show SiO4 units, grey polyhedra show ZnO4 units, and red spheres represent O atoms. (b) Rietveld difference plot for the single-phase refinement of Cs2ZnSi5O12 from synchrotron X-ray powder diffraction data collected at 8 K. The red, blue, and grey lines show respectively, the observed, calculated, and difference plots. Calculated Bragg reflection positions are indicated by green crosses. 2.2. Synchrotron X-ray powder diffraction Each sample was loaded into 0.3 mm diameter borosilicate glass capillaries and mounted on the liquid helium cryostat on the DORIS-III synchrotron B2 powder diffraction beamline [17]. Synchrotron X-Ray powder diffraction data, using 18keV energy X-rays, were collected at the lowest possible tempe- rature for each sample (8 K, X = Cu, Zn; 10K X = Cd) using the OBI image plate detector [18]. 2.3. X-ray powder diffraction data analysis All Bragg reflections in all low temperature powder diffraction patterns could be indexed in the space group Pbca with similar but slightly smaller (due to thermal contraction) lattice parameters to the ambient temperature structures for Cs2XSi5O12 (X = Cu [11], Zn [10], Cd [8]). These ambient tempe- rature structures, with complete T-site cation ordering, were used as starting models for Rietveld [19] refinements using FULLPROF [20]. In all three refinements the isotropic atomic displacement parameters were constrained to be the same for all framework sites occupied by the same element, each Si site had the same displacement parameter as did each O site, although the O site parameters were different to that for Si sites. In the refinements for X = Cd and Zn the O isotropic atomic displacement parameters could not be refined to positive values, so these parameters were kept fixed. Soft constraints were used for Si–O and X–O distances in all three refinements. For X = Cu the Si–O and Cu–O distances were constrained (±0.01 A� ) to be those from the ambient temperature structure of Cs2CuSi5O12 [11]. Similarly, for X = Cd the Si–O and Cd–O distances were constrained (±0.01 A� ) to be those from the ambient temperature structure of Cs2CdSi5O12 [8]. However, as the refined crystal structure for X = Zn, from high resolution synchrotron X-ray powder diffraction data [10], did not have complete T-site cation order and the T–O distances from this structure were not used for soft constraints. A starting model for X = Zn with complete T-site cation ordering was used. The range of Si–O distances for silicates is 1.59-1.63 A� , [21]. Therefore Si–O distances were constrained to be 1.61±0.01 A� . The Zn–O distances were constrained to be 1.93±0.01 A� as this was the soft constraint distance used at the start of the structural refinement for X = Zn [10]. Anthony Martin Thomas Bell / European Journal of Chemistry 12 (1) (2021) 60-63 63 2021 – European Journal of Chemistry – CC BY NC – DOI: 10.5155/eurjchem.12.1.60-63.2089 3. Results and discussion Low temperature Rietveld refinements on all three Cs2XSi5O12 (X = Cu, Cd, Zn) leucite analogues showed that the structures were all similar to the fully T-site cation ordered ambient temperature structures, no low temperature phase transitions were observed in each sample. The only significant differences were smaller unit cell volumes due to thermal contraction. It should be noted that for X = Cd, the low temperature lattice parameter is larger than the corresponding ambient temperature parameter. Similarly, for X = Zn the low temperature b lattice parameter is larger than the corres- ponding ambient temperature parameter. However, for all three structures, the low temperature unit cell volumes were smaller than the corresponding ambient temperature volumes. Table 1 shows the refined low temperature crystal structure parameters for each leucite analogue; the ambient temperature lattice parameters are also given for comparison. Figures 1a and 1b, respectively, show the VESTA [22] crystal structure plot and Rietveld difference plots for X = Cu. Similarly Figures 2a and 2b show the crystal structure plots and Rietveld difference plots for X = Cd, Figures 3a and 3b show the crystal structure plots and Rietveld difference plots for X = Zn. Table 1 and Figures 3a, 3b and 3c show that the R-factors and difference plot fit for X = Cd is slightly worse than for X = Cu and Zn. This may be due to some preferred orientation in the X = Cd sample. 4. Conclusions Low temperature synchrotron X-ray powder diffraction data collected on all three synthetic Cs2XSi5O12 (X = Cu, Cd, Zn) leucite analogues show that in all cases the Pbca cation ordered ambient temperature structures are retained. The only significant changes are due to thermal contraction. No low temperature phase transitions are observed. These are the first low temperature crystal structures determined for cation ordered leucite analogues. Acknowledgements The author wishes to thank Professor Michael Henderson of the University of Manchester for sample preparation. The author also wishes to thank Andreas Berghauser and Dr. Manuel Hinterstein for help with synchrotron X-ray powder diffraction data collection on the DORIS-III B2 powder diffraction beamline. Supporting information Further details of the crystal structure investigation(s) may be obtained from FIZ Karlsruhe, 76344 Eggenstein- Leopoldshafen, Germany, (fax: (+49)7247-808-666; e- mail: crysdata@fiz-karlsruhe.de, on quoting the deposition numbers CSD-2059131, -2059132, and -2059133. Disclosure statement Conflict of interests: The author declare that they have no conflict of interest. Ethical approval: All ethical guidelines have been adhered. Funding No external funding was used for this work, this work was part of in-house research done when the author was employed on the DORIS-III synchrotron at the DESY Laboratory, Notkestrasse 85, 22607 Hamburg, Germany. ORCID Anthony Martin Thomas Bell https://orcid.org/0000-0001-5038-5621 References [1]. Mazzi, F.; Galli, E.; Gottardi, G. Am. Mineral. 1976, 61 (1–2), 108–115. [2]. Dimitrijevic, R.; Dondur, V.; Petranovic, N. J. Solid State Chem. 1991, 95 (2), 335–345. [3]. Gatta, G. D.; Rotiroti, N.; Fisch, M.; Kadiyski, M.; Armbruster, T. Phys. Chem. Minerals 2008, 35 (9), 521–533. [4]. Bell, A. M. T.; Henderson, C. M. B. J. Solid State Chem. 2020, 284, 121142. [5]. Bell, A. M. T.; Henderson, C. M. B. Acta Crystallogr. C 1994, 50 (7), 984– 986. [6]. Bell, A. M. T.; Henderson, C. M. B.; Redfern, S. A. T.; Cernik, R. J.; Champness, P. E.; Fitch, A. N.; Kohn, S. C. Acta Crystallogr. B 1994, 50 (1), 31–41. [7]. Bell, A. M. T.; Henderson, C. M. B. Acta Crystallogr. 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H.; Berghaeuser, A.; Ehrenberg, H.; von Seggern, H.; Fuess, H. Nucl. Instrum. Methods Phys. Res. A 2004, 521 (2–3), 565–570. [19]. Rietveld, H. M. J. Appl. Cryst. 1969, 2 (2), 65–71. [20]. Rodriguez-Carvajal, J. Physica B: Condensed Matter 1993, 192 (1–2), 55–69. [21]. International Tables for X-ray Crystallography, volume III, Table 4.1.1. International Union of Crystallography, Pub. by Kynoch Press, 1975. [22]. Momma, K.; Izumi, F. J. Appl. Cryst. 2008, 41 (3), 653–658. Copyright © 2021 by Authors. This work is published and licensed by Atlanta Publishing House LLC, Atlanta, GA, USA. The full terms of this license are available at http://www.eurjchem.com/index.php/eurjchem/pages/view/terms and incorporate the Creative Commons Attribution-Non Commercial (CC BY NC) (International, v4.0) License (http://creativecommons.org/licenses/by-nc/4.0). By accessing the work, you hereby accept the Terms. This is an open access article distributed under the terms and conditions of the CC BY NC License, which permits unrestricted non-commercial use, distribution, and reproduction in any medium, provided the original work is properly cited without any further permission from Atlanta Publishing House LLC (European Journal of Chemistry). No use, distribution or reproduction is permitted which does not comply with these terms. Permissions for commercial use of this work beyond the scope of the License (http://www.eurjchem.com/index.php/eurjchem/pages/view/terms) are administered by Atlanta Publishing House LLC (European Journal of Chemistry). mailto:crysdata@fiz-karlsruhe.de https://orcid.org/0000-0001-5038-5621 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms http://creativecommons.org/licenses/by-nc/4.0 http://www.eurjchem.com/index.php/eurjchem/pages/view/terms 1. Introduction 2. Experimental 2.1. Sample preparation 2.2. Synchrotron X-ray powder diffraction 2.3. X-ray powder diffraction data analysis 3. Results and discussion 4. Conclusions Acknowledgements Supporting information Disclosure statement Funding ORCID References PrintField10: PrintField11: PrintField12: PrintField13: PrintField20: PrintField21: PrintField22: PrintField23: