ESR STUDY OF ELECTRON-NUCLEAR DIPOLAR RELAXATION FOR ASO44- SPIN-PROBE IN THE PARAELECTRIC PHASE OF KH2ASO4

Saturation behavior of allowed and forbidden ESR transition of AsO44- paramagnetic probe in KH2AsO4 was studied in the wide temperature inte rval around the paraelectric - ferroelectric phase transition, T-c. Th e ratios between forbidden and allowed line intensities were employed to deduce information on the electron-nuclear dipolar (END) relaxation mechanism. It was shown that a proton END relaxation mechanism exhibi ts an extremal temperature behavior in the paraelectric phase around 2 30 K. The extremal temperature behavior was described by employing a m odel of proton hopping along the O-H ... O bonds around the paramagnet ic centers, and the correlation time of this hopping was estimated in the wide temperature range in the paraelectric phase (150-330 K) The t emperature dependence of effective proton distance from the neighbor o xygens was obtained, and it was discussed in terms of a localization o f the spin density on these oxygens caused by charge inbalance in the As-O bonds in the ferroelectric phase. (C) 1997 Academic Press.