Raman Scattering Study of the Phase Transitions in (NH4)2Cd2(SO4)3
Di-ammonium di-cadmium sulfate (CAS) belongs to the langbeinite structure, with space group T4 containing four formula units in the primitive cell [1,2]. JONA and PEPINSKY  were the first to discover the existence of a phase transition in this crystal. The low-frequency dielectric studies by OSHIMA and NAKAMURA  showed that ε(0) remains practically constant from room temperature to about 95 K, where it suddenly jumps to a higher value, which decreases exponentially on lowering the temperature further. The sudden jump in ε(0) is accompanied by a paraelectric-ferroelectric phase transition with the appearance of a constant spontaneous polarization . For these reasons, CAS is known as an improper ferroelectric.
KeywordsStructural Phase Transition Ferroelectric Phase Sudden Jump Soft Zone Ferroelectric Transition
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