Crystal growth of ferroelastic K 2Cd 2(SO 4) 3 and the K 2SO 4-CdSO 4 phase diagram

Abstract

Crystals of congruently melting K 2Cd 2(SO 4) 3 (having the langbeinite structure with a ferroelastic transition temperature of 156°C) were grown by the Bridgman and Czochralski techniques. The former yielded colorless crystals when using oxygen under pressure; the latter yielded tan crystals of slightly smaller unit cell volume and are assumed to be oxygen deficient. The ferroelastic transition was studied by thermal expansion measurements. Reexamination of the phase diagram showed the existence of a previously unreported phase K 6Cd(SO 4) 4 which is stable only between 520°C and the melting point of about 890°C.