Dielectric Spectroscopy of Relaxors and Dipolar Glasses

Abstract

In the present publication we report the results of dielectric spectroscopy investigations of two classes of materials—relaxors and dipolar glasses. As model relaxor was chosen PLZT 8/65/35 concentration. The real distribution function of the relaxation times f(τ) of the relaxor ferro-electric ceramics PLZT 8/65/35 and 9.5/65/35 was calculated from the dielectric measurements results in the wide frequency range (10¹–10¹² Hz). Below the Burns temperature T_B = 620 K, when the clusters begin to appear on cooling, the distribution function of the relaxation times is symmetrically shaped. On cooling the dispersion and loss spectra strongly broaden and slow down, the f(τ) function becomes asymmetrically shaped and the second maximum appears. The width of the f(τ) function was calculated at different temperatures. The longest relaxation times diverge according to the Vogel-Fulcher law with the freezing temperature 299 and 252 K for the 8/65/35 and 9.5/65/35 samples, respectively. The shortest relaxation time is about 10⁻¹² s and it remains almost temperature independent. Similar behaviour was observed in dipolar glasses BP/BPI. Much more information was obtained from two dimensional distribution of the relaxation times. This result confirmed Meyer—Neldel law in relaxors and dipolar glasses.

Keywords:

• Dielectric spectroscopy
• dipolar glasses
• distribution of relaxation times
• Meyer–Neldel law

Acknowledgments

This work was supported by the COST 539 “ELENA” action and Lithuanian Science and Study Foundation.