Dielectric properties in the vicinity of the ferroelectric phase transition in a mixed crystal of deuterated betaine phosphateo0.03 betaine phosphite0.97

The dielectric behaviour of ferroelectric hydrogen bonded deuterated betaine phosphate(0.03) betaine phosphite(0.97) (DBP0.03DBPI0.97) is investigated in the region of the ferroelectric phase transition. Dielectric dispersion is investigated in the frequency range up to 12 GHz. The dielectric dynamics shows a critical slowing down. The frequency of the relaxational soft mode in the paraelectric phase varies according to the quasi-one-dimensional Ising model and decreases up to 0.31 GHz at the phase transition temperature (T-C = 272 K). The obtained activation energy for the deuteron flipping motion DeltaU = 2.3kT(C) = 0.054 eV shows the order-disorder character of the ferroelectric phase transition. The spontaneous polarisation, obtained from pyroelectric measurements, is also well explained using the quasi-one-dimensional Ising model. At low temperatures, the freezing phenomena in DBP(0.03)DBPI(0.9)7 revealed the complex dielectric permittivity behaviour characteristic for the transition into the dipolar glass state. The activation energy of this low temperature process was found to be E-b = 1297 K (0.041 eV) and the glass temperature was estimated to 73 K. (C) 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.