Oxygen deficiency and grain boundary-related giant relaxation in Ba(Zr,Ti)O3 ceramics

Abstract

The influence of the oxygen vacancies on the dielectric response of BaZr0.10Ti0.90O3 ceramics prepared by solid-state reaction and sintered at 1400 °C for 2 h was investigated. The as-sintered ceramic exhibits a giant relaxation with a shift of the transition temperature from ∼85 °C to above 170 °C in the frequency ranges of 1 Hz–100 kHz, with high losses above unity and two components in the complex impedance plot. A complex dielectric relaxation response, with at least two thermally activated defect mechanisms with activation energies of ∼0.2 eV below the transition temperature and ∼0.7 eV for higher temperatures in the range of 85 °C–170 °C was determined. The observed giant relaxation is an extrinsic effect related to the oxygen deficiency, inhomogeneous distributed in the ceramic grain and not to the relaxor behavior of this system. After a post-annealing treatment at 1000 °C for 50 h, the dielectric response is completely changed: the permittivity vs. temperature dependences present maxima located at around Tm ≈ 90 °C, with almost no frequency dispersion. The conductivity spectra remained almost unchanged after the annealing, showing that the level of oxygen deficiency in this case is related to dielectric relaxations and not to the ac-conductivity dispersion. Two thermally activated dielectric relaxation processes were still identified, but with activation energies of ∼2.7 eV below the transition temperature and of ∼0.87 eV for higher temperatures in the range of 85 °C–170 °C. The high frequency relaxation process is almost suppressed by the reoxidation and its activation energy increased with more than one order in magnitude. One single component in the complex impedance plot found after reoxidation shows that the annealing allowed the homogenization of the oxygen level within the ceramic grains.