Bistable Fluctuation of SeO₄^3-Centers Doped in Partially Deuterated KH₂PO₄Observed by ESR

Abstract

Temperature dependence of 77 Se hyperfine structure of SeO 4 3- radicals doped in KH 2(1- x ) D 2 x PO 4 is measured. It is found that the spectrum-splitting temperature T t for low-D crystal (\(x \lesssim 0.4\)) is nearly constant (160 K–170 K) and T t for high-D one (\(x \gtrsim 0.5\)) coincides with the respective Curie temperature. This D-dependence of T t is compatible approximately with the picture of D-independent bistable fluctuation of PO 4 . But temperature dependence of the rate of bistable fluctuation of SeO 4 3- is found to depend on x . This D-dependence is explained qualitatively by introducing interactions among the PO 4 dipoles mediated by the electric dipoles on the hydrogen bonds, effective moment of which depends on dynamical behavior of the hydrogen nuclei. It is pointed out that the present result is also compatible with both the local freeze-out model and the geometrical isotope effect.