Influence of annealing atmosphere on the electrical and spectral properties of Gd_0.8Ca_0.2BaCo₂O_5+δ ceramic

For practical applications, the stability of perovskite-like oxides in various environments should be evaluated. In this work, samples of Gd_0.8Ca_0.2BaCo₂O_5+δ (GCBC2)were annealed in different atmospheres and at different temperatures, and changes in their spectral reflective properties, infrared radiative properties, and electrical conductivity properties under solar irradiation were investigated using thermogravimetric analyses, reflection spectra measurements, electrical conductivity measurements, and X-ray photoelectron spectroscopy. The results of the study show that oxygen non-stoichiometry is dependent on the temperature and atmosphere used during the annealing process. In an oxygen atmosphere, an increase in oxygen non-stoichiometry was observed up to temperatures of 500 °C, and then a decrease at 800 °C. In a nitrogen atmosphere, oxygen stoichiometry always decreased at temperature above 400 °C. Although an increase in oxygen content had no effect on the ceramic’s electrical and optical properties, a decrease in oxygen content affected its properties significantly. Therefore, because GCBC2 has a typical insulator–metal transition under solar irradiation below 500 °C, and a low infrared emissivity in oxidized atmospheres, it can be used as a solar thermal conversion material, or for spacecraft thermal control devices in an oxidized environment.