Synthesis and characterisation of the new cubic phase CsVTeO5 and re-investigation of the pyrochlore CsVTeO6

Abstract

The compound CsVTeO5 has been synthesized by solid state reactions and studied by X-ray powder diffraction. CsVTeO5 is polymorphic with a cubic high temperature variety, space group Fd3m and a=10.482(2). The observed X-ray powder pattern of this cubic phase is similar to the AB2O6 pyrochlore-type structure and also to those reported for ATiXO5 phases (A=Rb, Cs, Tl and X=P, As). These phases correspond to the high temperature cubic polymorph of KTiOPO4 (KTP). The framework of these cubic phases consists of randomly disordered TiO6 octahedra and XO4 (X=P, As) tetrahedra with the A+ cation occupying large cavities within this framework. The cubic phase 6' [a=10.483(1)], previously reported as a pyrochlore-type structure, corresponds in fact to CsVTeO5. The cubic CsVTeO6 phase, with a pyrochlore related structure, has also been synthesized and the structure was refined by Rietveld profiling of the X-ray data. The space group is Fd3m with a=10.077(1). The value of the unit cell parameter is in good agreement with those reported for the ABTeO6 pyrochlore series (A=K, Rb, Cs and B=Nb, Ta). The thermal stabilities of CsVTeO5 and CsVTeO6 under argon and oxygen atmospheres are discussed.

References

1. J. Darriet, G. Guillaume and J. Galy, C. R. Acad. Sci. Paris, Sér. C, 1969, 269, 23.
2. J. Darriet, G. Guillaume, K. A. Wilhelmi and J. Galy, Acta Chem. Scand., 1972, 26, 59.
3. J. Darriet, Bull. Soc. Fr. Minéral. Cristallogr., 1973, 96, 97.
4. S. Garcia-Martin, M. L. Veiga, A. Jerez, M. Gaitan and C. Pico, J. Chem. Soc., Dalton Trans., 1988, 2141.
5. J. Rodriguez-Carvajal, Program Fullprof, version 3.2, Laboratoire Léon Brillouin, CEA-CNRS, Saclay, January 1997.
6. L. K. Cheng, E. M. McCarron III, J. Calabrese, J. D. Bierlein and A. A. Ballman, J. Cryst. Growth, 1993, 132, 280.
7. L. K. Cheng, L. T. Cheng, F. C. Zumsteg, J. D. Bierlein and J. Galperin, J. Cryst. Growth, 1993, 132, 289.
8. M. Kunz, R. Dinnebier, L. K. Cheng, E. M. McCarron, D. E. Cox, J. B. Parise, M. Gehrke, J. Calabrese, P. W. Stephens, T. Vogt and R. Papoular, J. Solid State Chem., 1995, 120, 299.
9. I. Tordjman, R. Masse and J. C. Guitel, Z. Kristallogr., 1974, 139, 103.
10. R. D. Shannon, Acta Crystallogr., Sect. A, 1976, 32, 751.
11. B. Darriet, M. Rat, J. Galy and P. Hagenmuller, Mater. Res. Bull., 1971, 6, 1305.
12. M. A. Subramanian, G. Aravamudan and G. V. Subbarao, Prog. Solid State Chem., 1983, 15, 55.
13. B. G. Hyde and S. Andersson, in Inorganic Crystal Structures, John Wiley and Sons, New York, 1989, p. 344.