Structural Study of Phase Transition in K₂Co₂(SO₄)₃Crystals

Abstract

Crystal structure of K 2 Co 2 (SO 4 ) 3 was determined at nine temperatures in the high-temperature cubic phase. In contrast to the early structural study, the split-atom calculation concludes that the SO 4 ion has a number of equilibrium arrangements. Mean-square atomic displacements become large with approaching the phase transition temperature despite no soft mode has been found. Atomic distances between Co and O are fairly shorter than the normal distance in the average structure. We explain these results by assuming that the nuclei of the low-temperature phase have already been generated in the cubic phase.