Cation size effect on the thermochromic properties of rare earth cobaltitesRECoO3(RE: La, Nd, Sm)

International audienceRECoO3 (RE: rare earth) perovskite thin films have been deposited at room temperature by DC co-sputtering and subsequent annealing in air at 923 K during 1 day. The effect of the octahedra tilts on the optical properties has been tracked decreasing the RE cation size. The bending and stretching vibrational modes of the CoO6/2 octahedra give informations on the Co-O distances and the Co-O-Co angles which determine the Co-O overlap integral and hence the electric properties of these perovskites. Transmittance measurements in the 1.42 - 100 μm wavelength range show a high transparency at room temperature. When temperature increases an optical screening effect depending on the RE 3+ ionic radii (i.e. Co- O-Co angles) and resulting from the electrical behaviour occurs. At the wavelength of 8 μm, the transmittance drops from about 90% at room temperature to 50% at the temperature of 516, 600 and 640 K for LaCoO3, NdCoO3 and SmCoO3, respectively