Preparation Technology&Electrical Property Of Lanthanide Perovskite Oxide Coatings

Lanthanide perovskite composite oxides (LaMO3, M=Cr or Mn) have the advantages of strong ability of acid and base resistance, steady physicochemical properties at high temperature. Substitute of some alkaline-earth metal ions for partial of La sites, or some transition metal ions for partial of M sites, can change the electrical, magnetic, optical and catalytic properties of the oxide materials, while the crystal structure almost maintains stable, so it has attracted wide attention on semiconductor, superconductor, luminescent materials and catalyzer. By taking LaMnO3and LaCrO3material as the research object, it was explored in this paper that the application potential of them in the thermal sensitive coating, electrical heating coating and thermal control coating. The two kinds of coatings were prepared by the screen-printing method, respectively using La1-xSrxMn03powders and La1-xCaxCrO3powders synthesized by the sol-gel method. The effects of preparation technology and doping content on coating quanlity and electrical conductivity were investigated, and the conductive mechanism at different temperature regions and the metal to insulating phase transition of La1-xSrxMnO3coatings at were discussed. The research contents and conclusions are follows:(1) Effects of the key preparation technology parameters of the screen printing method on quanlity and electrical conductivity of La1-xSrxMn03(x=0.1-0.5) coatings were investigated. It was indicated that the coatings prepared with stainless steel screen had better surface quanlity and uniform conductivity. The coatings prepared with the contact printing method were thinner than the non-contact printing method; moreover the coatings prepared with the screens of higher mesh were uniform and had a lower conductivity and better surface quanlity than others. The conductive mechanism of the coatings with different meshes between400K and700K is consistent with the adiabatic small polaron hopping model, and the screen mesh has little effect on the conductivity activation energy.(2) The screen printing technology of La1-xCaxCrO3(x=0.1、0.2、0.3) coatings was discussed according to the coating quanlity and electrical conductivity. These coatings showed a bad characteristics with the sintering temperature from1200℃to1400℃, including poor strength and bond strength, great sheet resistance, so the preparation technology still needed a more promotion.(3) It was studied that variation of resistivity of La1-xSrxMnO3coatings after absorbing heat, and the conductivity mechanisms were discussed at different temperature regions. La1-xSrxMn03coatings present metal-type conductivity at low temperature region, and insulator-type conductivity at high temperature region. At the region from80K to700K, both Lao.9Sr0.1Mn03and La0.5Sr0.5Mn03coatings do not present the Metal-Insulator translation point Tp. Tp points of La0.8Sro.2Mn03, Lao.7Sro.3MnO3and La0.6Sr0.4MnO3are at103K,208K and236K respectively. The temperature at the translation point increases with increasing the content of strontium. At the region from400K to700K, La1-xSrxMnO3coatings present insulator-type conductivity, and variation of the resistivity is consistent with Adiabatic Small Polaron Hopping (ASPH) conductivity model. Moreover, La0.7Sr0.3MnO3and La0.6Sro.4MnO3coatings present electron-electron scattering mechanism between88K and135K. Due to the competition between metal phase and insulator phase, the variation of experimental resistivity of Lao.6Sro.4Mn03coating is more consistent with the percolation medel.(4) Effect of strontium content on the electrifying heating results of LaMnO3-based coatings was investigated in this paper, such as heating temperature and infrared radiation wavelength. The heating temperature of La0.6Sr0.4MnO3coating could reach800℃, furthermore it can be kept above500℃for a long time through controlling input voltage. This shows that these coatings can be developed to electrical heating coating. While the heating temperature of the coatings with different strontium contents is between90℃and360℃, the infrared radiation wavelength locates in the region from4000nm to5000nm. The peak moves to the short wavelength with increasing heating temperature, and the higher of the heating temperature is, stronger of the relative radiation energy is, however, the strontium extent has a little effect on the relative radiation energy of the coating.