Dielectric relaxation in the weak ferroelectric Li2Ge7O15 near the ferroelectric phase transition

The dielectric permittivity of Ni-doped Li2Ge7O15 crystals was studied in t he vicinity of the ferroelectric phase transition. Introduction of Ni has b een shown to suppress the dielectric anomaly and to reduce substantially th e transition temperature. A temperature hysteresis in epsilon (T) has been observed in nominally pure and Ni-doped Li2Ge7O15 crystals near the transit ion point. Measurements performed under cooling from the paraphase reveal d ispersion of dielectric permittivity at Debye relaxation frequencies of the order of 10(4) - 10(5) Hz at T-c. It is proposed that the hysteresis pheno mena and the low-frequency dispersion are caused by residual defects (of th e type of random local fields), which become polarized in the ferroelectric phase and become disordered above T-c. (C) 1998 American Institute of Phys ics. [S1063-7834(98)01312-4].