Anomalous thermoelastic behaviour of cubic potassium cyanide

Abstract

The temperature dependence of all elastic constants of cubic potassium cyanide has been measured by ultrasonic methods in the range from -105.4 to 181°C. Until about 180°C all elastic wave velocities increase with higher temperatures. The behaviour of the shear constant c44 is given by c44 = a · log T/T0 with a = 0.219 · 1011 dyn.cm-2 and T0 = 153.7°K with a good approximation. These unusual effects are assigned to the librational vibrations and orientational jumping processes of the CN-ions. The phase transition at -105.5°C is a consequence of the low c44 value. © 1973.