Temperature dependence of the structure of the antifluorite K2OsCl6: evidence for precursor tetragonal clusters near TC

Abstract

Neutron-diffraction profiles were obtained from a powder sample of K2OsCl6. Measurements were taken at six temperatures above TC, the temperature of the cubic-to-tetragonal structural phase transition, and at one temperature below TC. Profile-refinement analysis yielded temperature-dependent Debye–Waller factors that behaved as expected from the elastic properties of a harmonic cubic crystal. Of intrinsic interest is the conclusion that the data contain the first neutron-diffraction evidence for the occurrence of precursor clusters. These long-lived fluctuations, which possess the symmetry of the tetragonal phase but which occur in the cubic phase, were first identified from chlorine nuclear quadrupole relaxation data in K2OsCl6.