Structural And Magnetic Properties Of Some Vacancy Ordered Osmium Halide Perovskites

Abstract

The structures and magnetic properties of the Os4+ (5d4) halides K2OsCl6, K2OsBr6, Na2OsBr6 and Na2OsBr6.6H2O are described. K2OsCl6 and K2OsBr6 have a cubic vacancy-ordered double perovskites structure but undergo different symmetry lowering structural phase transitions upon cooling associated with a combination of the relative size of the ions and differences in their chemical bonding. The structure of Na2OsBr6.6H2O has been determined for the first time and the thermal stability of this established using a combination of in-situ diffraction and TGA. Na2OsBr6.6H2O and Na2OsBr6 are isostructural with the analogous iridium chlorides, Na2IrCl6.6H2O and Na2IrCl6, dehydration proceeds via different intermediate phases. The magnetic moments of four compounds display Kotani-like behaviour consistent with a Jeff = 0 ground state, however the magnetic susceptibility measurements reveal unusual low temperature properties indicative of a weakly magnetic ground state.