Thermochromic La1−xSrxMnO3 (x=0.1, 0.175, and 0.3) smart coatings grown by reactive pulsed laser deposition

Abstract

Thermochromic La1−xSrxMnO3 (x=0.1, 0.175, and 0.3) (LSMO) smart coatings were synthesized on (100) silicon and (0001) sapphire substrates by means of reactive pulsed laser deposition process at relatively low substrate temperature (500°C) and without postannealing. X-ray diffraction patterns indicated that all deposited LSMO films have polycrystalline structures. The energy dispersive x-ray spectroscopy analysis indicated approximately the same La∕Sr ratio in the formed LSMO coatings as in their corresponding targets. While, the x-ray photoelectron spectroscopy analysis of the LSMO/sapphire revealed that the strontium segregate at the film surface. The thermochromism of LSMO coatings was investigated by measuring their infrared reflectance as a function of temperature (up to 160°C). It was observed that the reflectance decreased as the temperature increased. Reflectance switching of about 25% was achieved in La0.7Sr0.3MnO3∕Si at a wavelength of 5μm. The sheet electrical resistivity as a function of temperature (up to 130°C) of LSMO/sapphire was investigated by means of the standard four-point probe technique. The resistivity decreased with increasing the temperature and no metallic-to-insulator transition was observed. However, it is found that the resistivity is very sensitive to the concentration level of Sr dopant: the resistivity decreased as the concentration of Sr increased. In addition, at room temperature, a higher temperature coefficient of resistance of −2.30%∕°C was achieved in La0.9Sr0.1MnO3 thin films. Finally, these LSMO smart coatings are promising materials for optical switching and IR uncooled bolometer devices.