Galati, R., Simon, C., Henry, P.F. and Weller, M.T.
Cation displacements and the structures of the superconducting pyrochlore osmates AOs(2)O(6) (A = K, Rb, and Cs)
Physical Review B, 77, (10) (doi:10.1103/PhysRevB.77.104523).
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Variable temperature, 2 K<T<500 K, powder neutron diffraction studies of the beta-pyrochlores AOs2O6 and ANbTeO6, A=K, Rb, and Cs, have been undertaken. Anomalous behaviors in the lattice parameter variations as a function of temperature for the superconducting osmates with A=K, and to a lesser extent for A=Rb, are associated with local, static displacements of the alkali metal cation, which occur below ~80 K. These displacements are random around the 8b position as modeled in the space group Fd-3m; no evidence for decrease in symmetry from Fd-3m was observed for any sample above 2 K. For the nonsuperconducting ANbTeO6, A=K, Rb, and Cs, phases, similar structural and lattice parameter behaviors are observed with localization of the potassium ions in KNbTeO6 below ~30 K.
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