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Modified strong dipole-proton coupling model and local properties of EPR probe in the KDP-type ferroelectrics

The modified strong dipole-proton coupling (MSDPC) model, which predicts several static and dynamic dielectric properties of KDP-type ferroelectrics, is used to investigate properties of paramagnetic center SeO43- introduced in KH2PO4 (KDP) and KD2PO4 (DKDP) lattice as a local probe in EPR experiment. Paramagnetic center is treated within MSDPC model as a "soft" impurity, with Aprobe value of the elastic constant for the dipole c-component induction lower than the A value for the original PO43- group. For Aprobe=0.45A, the MD simulations in the paraelectric phase of KDP and DKDP show the effective local double-well potential of the probe, and the temperature dependence of calculated correlation time τ for the dipole reorientational jumps over the barrier can be fitted by the Arrhenius law. The obtained Arrhenius parameters for KDP are close to the experimental ones, and the experimentally detected higher activation energy in DKDP is reproduced. Also, the high-temperature line broadening and the temperature dependence of 77Se hyperfine coupling observed in experiment are discussed within the MSDPC model.

KDP-type ferroelectrics; isotope effect; electron paramagnetic resonance; paramagnetic center

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