Pressure-induced disordering of sodium potassium sulfates and chromates
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213-3890 (United States)
Raman scattering and energy-dispersive x-ray diffraction in a diamond-anvil cell were used to study the salts NaKSO{sub 4}, K{sub 3}Na(SO{sub 4}){sub 2}, NaKCrO{sub 4}, and K{sub 3}Na(CrO{sub 4}){sub 2} to pressures of 22.5 GPa. These measurements reveal that the SO{sub 4} and CrO{sub 4} tetrahedra in the monopotassium salts become disordered, while those in the tripotassium salts stay ordered. This disordering occurs without a significant change in the structural arrangement of the cations. We suggest that the disordering results from an impeded ferroelastic phase transition, which causes the zone boundaries, and therefore the SO{sub 4} and CrO{sub 4} tetrahedra, to be distorted. The four salts are related to one of two structures: The tripotassium salts are isostructural, the monopotassium salts are closely related. The two structures differ by one symmetry element, which leaves the neighboring tetrahedra inequivalent. It is this difference that causes only one of the structures to form distorted zone boundaries. {copyright} {ital 1996 The American Physical Society.}
- DOE Contract Number:
- FG02-92ER45474
- OSTI ID:
- 383166
- Journal Information:
- Physical Review, B: Condensed Matter, Vol. 54, Issue 10; Other Information: PBD: Sep 1996
- Country of Publication:
- United States
- Language:
- English
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