Cation Size Effect On The Thermochromic Properties Of Rare Earth Cobaltites Recoo3 (Re: La, Nd, Sm)

RECoO3 (RE: rare earth) perovskite thin films have been deposited at room temperature by direct current co-sputtering and subsequent annealing in air at 923K 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 information 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 mu m wavelength range show a high transparency at room temperature. When temperature increases, an optical screening effect depending on the RE3+ ionic radii (i.e., Co-O-Co angles) and resulting from the electrical behaviour occurs. At the wavelength of 8 mu m, the transmittance drops from about 90% at room temperature to 50% at the temperature of 516, 600, and 640K for LaCoO3, NdCoO3, and SmCoO3, respectively. (C) 2013 AIP Publishing LLC.