Cation displacements and the structures of the superconducting pyrochlore osmates AOs2O6 (A=K, Rb, and Cs)
Rosa Galati, Charles Simon, Paul F. Henry, Mark T. Weller
DOI 10.1103/PhysRevB.77.104523 · Physical Review B
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Abstract
Variable temperature, 2K<T<500K, 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 ∼80K. 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 2K. 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 ∼30K.
Source-reported materials — not catalogue approval
| Formula | Reported Tc (K) | Pressure (GPa) | Type |
|---|---|---|---|
| KOs2O6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 9.6 | Pressure not reported | unknown |
| RbOs2O6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 6.3 | Pressure not reported | unknown |
| CsOs2O6 Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula. | 3.6 | Pressure not reported | unknown |
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