Dielectric spectroscopy of Pb(Mg_1/3Nb_2/3)O₃-PbTiO₃ single crystals

Complex impedance spectroscopic data were acquired on single crystals of the morphotropic phase boundary composition of 0.68Pb(Mg_1/3Nb_2/3)O₃-0.32PbTiO₃ over a wide range of temperatures (25-525°C) and frequencies 1 kHz-1 MHz. This study takes advantage of plotting ac data simultaneously in the form of impedance and modulus spectroscopic plots. This permits the easy interpretation of microscopic processes responsible for the measured ac response. Frequency explicit plots of imaginary components of impedance and modulus exhibit Debye-like peak shapes. The data for ac conductivity were computed from the impedance data and the activation energy for conduction at different frequencies was determined. Cole-Cole diagrams were plotted and these indicate the presence of a single relaxation process. The relaxation times determined from these plots followed an Arrhenius law, and the activation energy for relaxation was found to be 1.2 eV. The ac conductivity data was found to obey Jonscher's universal power law and resulted in a value of the exponent "n" =0.95.