Effect of sintering temperature on microstructure, electrical properties, and thermal expansion of perovskite-type La_0.8Ca _0.2CrO₃ complex oxides synthesized by a combustion method

Perovskite-type La_0.8Ca_0.2CrO₃ complex oxides were synthesized by a combustion method. Microstructural evolution, electrical properties, and thermal expansion behavior of the ceramics were investigated in the sintering temperature range of 1250 °C to 1450 °C. It was found that the electrical conductivity (σ_e) remarkably improved with increasing sintering temperature from 1250 C to 1400 C, ascribed to the development of microstructural densification, whereas it declined slightly above 1400 °C due to generation of excessive liquid. The specimen sintered at 1400 °C had a maximum conductivity of 31.6 S cm^-1 at 800 °C, and lowest activation energy of 0.148 eV. The improvement of the thermal expansion coefficient (TEC) with increasing sintering temperature was monotonic as a result of the microstructural densification of the materials. The TEC of La_0.8Ca_0.2CrO₃ sintered at 1400°C was about 10.5 × 10^-6 K^-1, being consistent with other components as high-temperature conductors. With respect to microstructure, electrical properties, and thermal expansion, the preferable sintering temperature was ascertained to be about 1400 °C, which is much lower than for the traditional solid-state reaction method.