Phase Transitions in Some Langbeinite-Type Crystals

Abstract

Phase transitions were searched in five langbeinite-type crystals in the temperature range 20∼-196°C. Dielectric and elastic anomalies were found at -72°C in a single crystal of K 2 Mn 2 (SO 4 ) 3 . Pyroelectric measurements showed that the low temperature phase of K 2 Mn 2 (SO 4 ) 3 is not polar. Dielectric and pyroelectric measurements were made on the polycrystalline samples of the solidified molten K 2 Zn 2 (SO 4 ) 3 and K 2 Cd 2 (SO 4 ) 3 . It was found that K 2 Zn 2 (SO 4 ) 3 undergoes pyroelectric phase transition at -137°C, but K 2 Cd 2 (SO 4 ) 3 does not show any phase transition. It was also found that K 2 Mg 2 (SO 4 ) 3 and Rb 2 Mg 2 (SO 4 ) 3 of pressed powder crystals do not show any phase transition signal.