Structural, thermal stability and electrical conductivity of zirconium substituted barium cerate ceramics

Abstract

Barium cerate perovskite ceramics substituted with zirconium BaCe1-xZrxO3 (x = 0, 0.05, 0.10, 0.15, 0.20) were prepared by the standard solid-state reaction route. The x-ray diffraction patterns affirmed the single-phase orthorhombic symmetry of the synthesized ceramics. The thermal stability of the samples has been checked by thermogravimetric analysis (TGA). TGA of dry and pre-hydrated (pH2O (g) ≈ 0.03 atm and 1.0 atm) compositions revealed that all the samples are stable up to a temperature of 800 °C. However, the samples treated at a higher partial pressure of water are found less stable. The crystalline phase of the studied compositions before and after TGA was measured with the Raman study, confirming that most of the parent phases exist or remain stable even after the treatment of samples at higher vapor pressure. Thermal stability gradually improved with increasing Zr-substitution. The TGA results that are consistent with the Raman studies proved the sample with x = 0.20 is the most stable among the studied compositions. Complex impedance spectroscopy studies clearly demonstrated the impact of bulk and grain boundary on the total resistance of the compounds with different zirconium contents. The Arrhenius dependence of the total conductivity indicates that the conductivity decreased with an increase in Zr concentration both in air and wet nitrogen atmosphere. Comparing the conductivity under both ambiances suggests that some additional charged species participate in the conduction mechanism under the wet environment. These are ascribed to the protonic defects, developing into barium cerate via extrinsic oxygen vacancies because of high-temperature sintering.