Frequency-temperature response of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by different precursors. Part II. Impedance spectroscopy characterization

Abstract

The dielectric behavior of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained using the traditional ceramic method employing three different precursors was investigated by impedance spectroscopy in the temperature range of 200–300°C. This study was carried out by means of the simultaneous analysis of the complex impedance Z̃, electric modulus M̃, and admittance Ỹ functions from the measurements in the frequency range of 20Hz–1MHz. In correspondence to a previous structural, morphological, and temperature response study, appropriate microstructural and equivalent circuit models were established. Based on the brick layer model, three series of interconnected electrically distinct regions are considered: a conductive grain boundary layer, a capacitive grain boundary surface layer, and a resistive-ferroelectric bulk layer. Two conduction mechanisms were identified: a dielectric relaxation process due to localized conduction associated with the presence of oxygen vacancies and the nonlocalized conduction corresponding to long range conductivity associated with extrinsic mechanisms due, fundamentally, to Fe2+ presence. Both mechanisms were discerned to occur inside the grains and where the contributions of the grain boundary are neglected. Three conductivity components were deconvoluted: a longe range dc conductivity at the low frequency region, a capacitive behavior at higher frequencies, and a universal power law behavior in an intermediate-frequency region. Values of the activation energy corresponding to relaxation processes and dc conductivity were determined and excellent correlation with those obtained from the temperature response was found. A comparative analysis between the behaviors of each sample is presented.