Samples of Sm0.5Sr0.5CoO3–δwere annealed in different atmospheres(Ar,N2,and O2)and temperatures(400 1200 oC),and changes in their masses,structures,surface transport properties,optical properties,and oxygen nonstoichiometries were investigated using thermogravimetric(TG)analyses,X-ray diffraction(XRD)analyses,electrical conductivity measurements,reflection spectra measurements,and X-ray photoelectron spectroscopy,respectively.The TG analyses,performed in air and an N2atmosphere,allowed us to determine the changes in the masses of the samples.The results of the XRD analyses elucidated the changes in the structure of the samples under different conditions.The XPS spectra and simulation data indicated that the number of oxygen defects generated in the samples depended on the temperature and atmosphere.At high temperatures,the surface conductivities and full-spectrum reflectivities of the samples decreased with an increase in the number of oxygen vacancies.In an oxidative atmosphere,the samples exhibited outstanding visible and near-infrared light absorption.Furthermore,the samples were highly sensitive to a reducing atmosphere at various temperatures.On the basis of the fact that the properties of Sm0.5Sr0.5CoO3–δvary with the environment,it has potential use in high-temperature applications such as weather sensors. Samples of Sm0.5Sr0.5CoO3-δwere annealed in different atmospheres (Ar, N2, and O2) and temperatures (400 1200 oC), and changes in their masses, structures, surface transport properties, optical properties, and oxygen nonstoichiometries were investigated using thermogravimetric (TG) analyzes, X-ray diffraction (XRD) analyzes, electrical conductivity measurements, reflection spectra measurements, and X-ray photoelectron spectroscopy, respectively. TG analyzes, performed in air and an N2 atmosphere, allowed us to determine the changes in the masses of the samples. the results of the XRD analyzes elucidated the changes in the structure of the samples under different conditions. XPS spectra and simulation data indicated that the number of oxygen defects generated in the samples depended on the temperature and atmosphere. At high temperatures, the surface conductivities and full-spectrum reflectivities of the samples decreased with an increase in the number of oxygen vacancies. an an oxidative atmosphere, the sample exhibits outstanding visible and near-infrared light absorption. Future samples, the samples were highly sensitive to a reducing atmosphere at various temperatures. On the basis of the fact that the properties of Sm0.5Sr0.5CoO3-δvary with the environment, it has potential use in high-temperature applications such as weather sensors.