Preparation Of Strontium Titanate-Based Thin-Films And Their Thermoelectric Properties

SrTiO₃-based materials are currently attracting a keen interest because of their practical application, such as coolers and industrial regenerators. The materials are considered as one of the most promising n-type thermoelectric materials because of their high-temperature, non-toxic, non-polluting, and low cost of preparation. Though SrTiO₃ is an insulator, SrTiO₃-based materials could be semiconductors by being electron-doped at Sr or Ti sites because the electron-doped could change the concentrations of carriers to improve the electric conductivity. What’s more, the films of thermoelectric materials have much better thermoelectric properties. In this thesis, the thermoelectric properties of SrTiO₃-based thin films were enhanced via doping La or adding Ag by sol-gel method.La_xSr_1-xTiO₃ and SrTiO₃/xAg thin films were prepared by sol-gel method. The composition and microstructures were characterized by XRD, AFM and SEM. The electrical conductivity , Seebeck coefficient S, power factor P of these films were also tested from 293K to 543K. Effects of sintering temperature, sintering atmosphere, La-doped or Ag-added on the microstructures and morphology were investigated. Furthermore, the relationships of thermoelectric properties with temperature, La-doped and Ag-added were studied.First, the SrTiO₃ thin films were obtained by using strontium acetate and tetra butyl titanate as raw materials, glacial acetic acid and ethylene glycol monomethyl ether as solvent. And the impacts of the sintering temperature, sintering atmosphere to the microstructures and morphology were investigated. Then the La_xSr_1-xTiO₃ （x=0.05,0.1,0.15,0.2） thin films were prepared by the same way of the SrTiO₃ thin films. What’s more, the La_xSr_1-xTiO₃ films were further sintered in Nitrogen and Hydrogen miscellaneous gas at 1473K for 60 minutes. And the results showed that in the temperature range the Seebeck coefficients, the electrical conductivities and the power factors of the films increase with increasing temperature. What’s more, the electrical conductivities increase with the La content. However, the Seebeck coefficients and the power factors first increase and then decrease with the La content. The La0.15Sr0.85TiO₃ films obtained at 1473K showed the highest power factor, reaching 4.75×10-7W·m-1·K-2 at 543 K.Secondly, the SrTiO₃/xAg（x=0,0.02,0.05,0.08,0.1） films were prepared by using silver nitrate, strontium nitrate and tetra butyl titanate as raw materials, distilled water, glacial acetic acid and ethylene glycol monomethyl ether as solvent. And the results showed that the Seebeck coefficients of the Ag-added films first increase and then decrease with the Ag content. The SrTiO₃/0.05Ag films showed the highest power factor of the investigated samples, reaching 8.87×10-8W·m-1·K-2 at 543 K. What’s more, in the temperature range the Seebeck coefficients, the electrical conductivities and the power factors of the films increase with increasing temperature.