Dielectric and impedance spectroscopic studies of lead-free barium-calcium-zirconium-titanium oxide ceramics

Abstract

Dielectric properties of perovsldte structured (Ba0.85Ca0.15)(Zr0.1Ti0.9)O-3; [BCZT], ferroelectric ceramics prepared by the conventional solidstate reaction method were investigated by AC impedance spectroscopy. To obtain high density samples, the pressed pellets were sintered at 1450 degrees C and 1500 degrees C for 4 h. Polarization-Electric field (P-E) measurements of the ceramic samples sintered at 1500 degrees C showed higher remnant polarization (P-r=12.20 mu C/cm(2)) and coercive field (E-c=4.50 kV/cm) values when compared to P-r=8.02 mu C/cm(2) and E-c=3.80 kV/cm respectively for the samples sintered at 1450 degrees C. In addition, BCZT sintered at 1500 degrees C showed higher dielectric constant as compared to the one sintered at 1450 degrees C. However, the dielectric constant measured as a function of frequency for both the sintered samples showed single maximum value at similar to 105 degrees C, which is attributed to the structural phase transition (Curie temperature, T-c) from ferroelectric, tetragonal phase to paraelectric, cubic phase. AC impedance analysis over the frequency range of 100 Hz to 1 MHz for the ceramic sintered at 1500 degrees C, showed mainly bulk contribution up to 250 degrees C while bulk and grain-boundary contributions were present above 250 degrees C. Activation energies for conductivity were found to be strongly frequency dependent. The activation energy values are attributed to the conduction of oxygen vacancies via hopping mechanism. (C) 2015 Elsevier Ltd and Techna Group S.r.l. All rights reserved.