Abstract
Accurate crystal structure of K_2Zn_2(SO_4)_3 was determined at seven temperatures in the high-temperature cubic phase. It turned out that the SO_4 ion has multi-site molecular arrangements. We also found that mean-square atomic displacements and extinction parameters of diffraction intensities become anomalously large with approaching the phase transition temperature. These peculiar features, which are also observed for other langbeinite-type crystals, are explained by assuming that nuclei of a low-temperature phase have already been generated in the high-temperature cubic phase. We discuss that the nuclei are produced by the short Zn--O distances.
