Elastic, thermoelastic and piezoelastic properties of crystals of the KSCN family (KN3, KHF2, KSCN, NH4HF2, NH4SCN)

Abstract

Abstract Large single crystals of KN3, KHF2, NH4HF2, KSCN and NH4SCN, which are structurally related to those of the CsCl type, were grown from aqueous solutions by controlled evaporation. Elastic, thermoelastic and piezoelastic constants were determined from ultrasonic resonance frequencies of thick plane-parallel plates. In addition, the tensors of thermal expansion were measured. Elastic properties and thermal expansion reflect the close relationship to the CsCl-type structure. The anisotropy is mainly caused by the preferential orientation of the long axes of the anionic dumb-bells within one distinct plane. KSCN exhibits weak elastic anomalies approaching the phase transition at 413 K. These effects, which are much smaller than those found in the high-temperature phases of the alkali cyanides, indicate, together with the almost missing hysteresis and the small transition enthalpy, a transition of mainly second order. The variation of the elastic behaviour of KHF2 and NH4SCN passing through the transition at 471 K and 367 K, respectively, express first-order processes.