EPR study of kinetic properties of a weak polar ferroelectric Li2Ge7O15

The EPR spectra of Mn2+ ions have been studied in the vicinity of the phase transition to the ferroelectric phase in lithium heptagermanate crystals. The anomalous broadening of the resonance lines observed in the vicinity of the transition temperature Te was attributed to an increase of the contrib ution of low-frequency (omega < 10(7) Hz) fluctuations of the local order p arameter. The critical index of the correlation length is determined to be nu approximate to 0.63, which indicates the Ising-type critical behavior of the crystal. The experimental data obtained in the vicinity of Te were int erpreted with due regard for long range dipole interactions. According to o ur estimates, the forces of dipole interactions are prevalent only in the c lose vicinity of the transition point, \T - T-C\ much less than 0.1 K. (C) 2000 MAIK "Nauka/Interperiodica".