Single-crystal and powder neutron diffraction investigations of thermal motions in K2PtCl6 as a function of temperature

By means of neutron diffraction the crystal structure and thermal motions of the ions in FCC K2PtCl6 were investigated in the temperature range from 20 to 380 K, extending the analysis to anharmonic terms, Associated with PtCl6 octahedra librations the Cl- ions vibrate mainly perpendicular to the Pt-Cl bonds. This thermal motion and also the isotropic thermal vibrations of the metal ions increase essentially with temperature, resulting in an isotropic thermal expansion. Within the experimental accuracy anharmonicity seems to be of minor importance.