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

Abstract

Dielectric properties of perovskite structured (Ba 0.85 Ca 0.15 )(Zr 0.1 Ti 0.9 )O 3 ; [BCZT], ferroelectric ceramics prepared by the conventional solid-state reaction method were investigated by AC impedance spectroscopy . To obtain high density samples, the pressed pellets were sintered at 1450 °C and 1500 °C for 4 h. Polarization–Electric field ( P – E ) measurements of the ceramic samples sintered at 1500 °C showed higher remnant polarization ( P r =12.20 µC/cm 2 ) and coercive field ( E c =4.50 kV/cm) values when compared to P r =8.02 µC/cm 2 and E c =3.80 kV/cm respectively for the samples sintered at 1450 °C. In addition, BCZT sintered at 1500 °C showed higher dielectric constant as compared to the one sintered at 1450 °C. However, the dielectric constant measured as a function of frequency for both the sintered samples showed single maximum value at ~105 °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 °C, showed mainly bulk contribution up to 250 °C while bulk and grain-boundary contributions were present above 250 °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.