Control of solar absorbance and thermal emittance of Cr-doped Sm_0.5Sr_0.5CoO₃

A new application of Sm_0.5Sr_0.5Co_1-xCr_xO₃ as a controlled near-infrared reflective inorganic oxide has been developed. Samples were prepared by a solid-state reaction to form a perovskite solid solution with an orthorhombic structure. Then, the effect of Cr³⁺ cation doping on the crystal structure, electrical conductivity, solar absorbance, and thermal emittance properties of the Sm_0.5Sr_0.5Co_1-xCr_xO₃ was investigated. The electrical conductivity decreases upon the substitution of Cr³⁺ ions for Co³⁺/Co⁴⁺ because of the appearance of Cr³⁺-O^2--Cr³⁺ and Co³⁺-O^2--Cr³⁺ units, reducing the amount of the Co³⁺-O-Co⁴⁺ network. The Cr³⁺ ions doped into Co³⁺ sites were found to enhance the solar absorbance from 68.2% to 91.6% and to simultaneously increase the infrared emittance from 0.25 to 0.93. The mobility of infrared optical phonons from free electrons decreases upon Cr³⁺ doping, which weakens the scattering effect and enhances the absorption. Based on these properties, we can control the Cr³⁺ dopant concentration of Sm_0.5Sr_0.5Co_1-xCr_xO₃ to meet our demands.