ESR Study of Electron–Nuclear Dipolar Relaxation for AsO44−Spin Probe in the Paraelectric Phase of KH2AsO4
✍ Scribed by B. Rakvin; D. Merunka
- Publisher
- Elsevier Science
- Year
- 1997
- Tongue
- English
- Weight
- 176 KB
- Volume
- 126
- Category
- Article
- ISSN
- 1090-7807
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✦ Synopsis
Saturation behavior of allowed and forbidden ESR transition K) was smaller by a factor of three from that ( Ç287 K) of AsO 40 4 paramagnetic probe in KH 2 AsO 4 was studied in the estimated from specific heat measurements (5). However, wide temperature interval around the paraelectric -ferroelectric more recent ESR and ENDOR studies on several KDP-type phase transition, T c . The ratios between forbidden and allowed lattices were performed, and an additional reaxation mechaline intensities were employed to deduce information on the nism due to an exponential broadening effect was noted (6electron -nuclear dipolar ( END ) relaxation mechanism. It was 8). Furthermore, the clear evidence that this exponential shown that a proton END relaxation mechanism exhibits an relaxation rate exhibits the same activation energy as the extremal temperature behavior in the paraelectric phase around activation energy for the local polarization fluctuation means 230 K. The extremal temperature behavior was described by that the microscopic origin for the exponential type of relaxemploying a model of proton hopping along the O -HrrrO ation rate is not quite clear (6-8). Therefore, it can be bonds around the paramagnetic centers, and the correlation time of this hopping was estimated in the wide temperature concluded that all these discrepancies reflect an uncertainty range in the paraelectric phase ( 150 -330 K ) . The temperature in a microscopic mechanism responsible for the T 1 process.
dependence of effective proton distance from the neighbor oxy-
Concerning the T 1 data in the KDA lattice, any attempt gens was obtained, and it was discussed in terms of a localization to fit these data with larger values of U D leads to large of the spin density on these oxygens caused by charge inbalance deviation of calculated data (9) from the reported experiin the As -O bonds in the ferroelectric phase. ᭧ 1997 Academic Press mental measurements (3, 4). It can be supposed that a Q D evaluated from the Raman relaxation mechanism is smaller than Q D obtained from specific heat, because explanations of