Deuterium Concentrations of H₂PO₄⁻ and NH₄⁺ Radicals in Partially Deuterated NH₄H₂PO₄

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The deuteration rates (D-rates) of H₂PO₄⁻ radicals (R_P) in partially deuterated NH₄H₂PO₄ crystals are measured by ESR of SeO₄³⁻ doped in the crystals. It is found that the phase transition temperatures (T_c) of the crystals depend linearly on R_P; T_c(R_P)=148+94R_P [K]. Using this relation and data about total D-rate of highly deuterated ADP obtained by others, D-rates of NH₄⁺ radicals (R_N) in the crystals are calculated. It is pointed out that the shift of T_c does not depend on R_N but on R_P.