Thermal radiative properties of (La_{1 - x}Sr_x)MnO_{3 - δ} thin films fabricated on yttria-stabilized zirconia single-crystal substrate by pulsed laser deposition

For application as a variable thermal emittance material in a recently-developed thermal control system for spacecraft, (La_{1 - x}Sr_x)MnO_{3 - δ} (LSMO) thin films with thicknesses of 1.2 μm, 2.5 μm, and 4.3 μm were fabricated on yttria-stabilized zirconia (100) substrates by a pulsed laser deposition and ex-situ annealing at 1123 K in air. All the films were dense and their surface roughness was much smaller than the thermal infrared (IR) wavelength. The films had (100) and (110)-preferred orientations, and the thicker films showed more preferable growth along the (100) orientation. Temperature-magnetization curves revealed that the LSMO films exhibited a metal-insulator transition near room temperature. The thermal emittance of the films estimated from IR reflectance spectra and black body radiation spectra exhibited large non-linearity near room temperature owing to the phase transition. The change in thermal emittance of the LSMO films that were more than 2.5 μm thick was comparable with that of the Ca-doped LSMO ceramic tiles already used as variable thermal emittance materials. Thus, this result clearly demonstrates that LSMO thin films with thickness of 2.5 μm can work as variable thermal emittance materials in the thermal control system for spacecraft.