Elastic softening in static shear modulii of orientationally disordered (KCN)x(RbCN)1−x mixed crystals

An extended three-body force shell model (ETSM) incorporated by the effect of TR coupling and anharmonicity has been applied to investigate the static shear modulii (c44) of (KCN)x(RbCN)1−x mixed crystals. The shear modulii computed between the composition range 0⩽x⩽1 for the temperature range from 140 to 380 K. The static elastic constants c44 computed by us show an anomalous behavior with variation in temperature and are in good agreement with ultrasonic measurement data. It also shows a softening in elastic modes at lower temperature.