engleski

ENDOR detection of charge-density redistribution accompanying the ferroelectrics transition in KH2PO4

ESR and electron nuclear double resonance (ENDOR) measurements have been carried out on SeO43-- doped KH2PO4 to probe changes in the charge density distribution at the various atomic nuclei of the PO43- unit. ESR measurements of the proton superhyperfine coupling show that in the paraelectric phase all four oxygens carry a time averaged spin density of about 0. 18 but ESR resolution is insufficient for studies in the ferroelectric phase. ENDOR data show that in the ferroelectric phase, the spin density becomes almost-equal-to 0.3 at the two oxygens near which the hydrogens localize, and only 0.05 on the other two. These results appear to support the theoretical model proposed by Bystrov and Popova, 3 according to which the spontaneous polarization of the KH2PO4-type of compounds originates from the charge imbalance in the P-0 bonds caused by proton localization, rather than the relative displacements of the K and P atoms. The new results also help understand the long-standing question as to why the magnitudes of superhyperfine couplings of the hydrogen-bonded protons are unexpectedly small.

electron-spin-resonance ; potassium dihydrogen phosphate ; low-frequency fluctuations ; nuclear double-resonance ; paramagnetic-resonance ; phase-transitions ; aso44 center ; relaxation ; nh4h2po4 ; dynamics

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