Phase Transition of KD2PO4 Studied by ESR of SeO43

Behavior of 77 Se hyperfine structure of DKDP: SeO 4 3- is reported in detail. The spectroscopic splitting tensor and the hyperfine interaction tensor are determined in both paraelectric and ferroelectric phases. The coercive electric field is measured to be 4.4[kV/cm]. The striking effect of deuteration on the temperature dependence of the hyperfine structure is successfully explained under an assumption that the rate of slow fluctuation of the Se atom in the SeO 4 3- is independent of deuteration in the paraelectric phase. It is pointed out that the results on Cr 5+ in KDP, DKDP, KDA and DKDA are quite different from those on SeO 4 3- in KDP and DKDP and AsO 4 4- in KDA and DKDA with respect to the deuteration effect on the rate of the fluctuation observed by ESR.

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