Cubic sodium cyanide, another crystal with KCN-type anomalous thermoelastic behaviour

The temperature dependence of all elastic constants of cubic NaCN, measured by ultrasonic methods at ca 15 MHz from the transition point at 10.55 to 200°C, exhibits a similar anomalous thermoelastic behaviour to cubic KCN. Within a wide temperature range all elastic wave velocities increase with higher temperature. The most characteristic feature of the anomalous behaviour is the softening of the shear constant c₄₄ approaching the transition temperature. It is given by c₄₄(T) ≃O.2144(T- T₀)/T₀ (10¹¹dyn cm^-2) with T₀ = 255.4 K. The extremely small velocity of the elastic transverse wave connected with c₄₄ makes NaCN highly suited for acousto-optical deflector devices.