Superspace-group approach to the phase transition of Cu{sub 8}GeSe{sub 6}
- National Inst. for Research in Inorganic Materials, Namiki, Tsukuba (Japan)
- Univ. of Lausanne (Switzerland). Inst. of Crystallography
The high- and low-temperature forms, i.e., phase I (stable above 328 K) and phase II (stable below 328 K), of Cu{sub 8}GeSe{sub 6} have been investigated by the powder X-ray diffraction method. Cu{sub 8}GeSe{sub 6} II is hexagonal with A = 12.6438(2), C = 11.7570(1) {angstrom}, Z = 6, and P6{sub 3}cm, and its structure is considered to be a superstructure of the high-temperature form, Cu{sub 8}GeSe{sub 6} I (hexagonal, a = 7.3164(4) {approx_equal} A/{radical}3, c = 11.7679(7) {angstrom}, Z = 2, and P6{sub 3}mc). Rietveld analysis of Cu{sub 8}GeSe{sub 6} I (350 K) and II (290 K) has been performed using diffraction data measured by a high-resolution powder diffractometer and synchrotron X-ray radiation. For Cu{sub 8}GeSe{sub 6} II, a four-dimensional superspace group for commensurate modulation, P6{sub 3}mc (1/3 1/3 0), with basic cell constants a = 7.2999, c = 11.7570 {angstrom} has been successfully applied (R{sub wp} = 0.054). The superspace-group description allows uniform treatment of both forms, and the phase transition of Cu{sub 8}GeSe{sub 6} is explained in terms of the presence and absence of commensurate modulation waves.
- OSTI ID:
- 696669
- Journal Information:
- Journal of Solid State Chemistry, Vol. 146, Issue 2; Other Information: PBD: Sep 1999
- Country of Publication:
- United States
- Language:
- English
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