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Iron-doped SnO \u003csub\u003e 2 \u003c/ sub\u003e ceramics and thin films research

Author: GuoJie
Tutor: ZhaoKunYu
School: Kunming University of Science and Technology
Course: Materials Science
Keywords: SnO2 Fe-doped Ceramics Thin films Pulsed laser deposition
CLC: TQ174.6
Type: Master's thesis
Year: 2011
Downloads: 2
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Abstract

With the further fast process of global industrialization, the energy crisis and environmental pollution problem has became more and more outstanding and they are the most grim challenges to human being right now. To investigative new environment-friendly energy materials has caught redouble attention from various countries in the world. Thermoelectric materials are one kind of functional materials which could achieve the direct interconversion between heat energy and electric energy. Since the thermoelectric materials has numerous advantages, such as simple in structure and maintenance, small in size, light in weight, none moving-element, noise-free, zero emission, high reliability and long performance life. Thermoelectric materials has wide application prospects and become one of the hotspots in the fields of materials science. Compare with the traditional thermoelectric materials, the oxide thermoelectric materials has many advantages, not only outstanding conductivity and seebeck coefficient, but also anti-oxidant, high temperature resistance and nontoxic. The oxide thermoelectric materials have been particular interest to researchers because of these advantages. SnO2 is a new-type wide bandgap semiconductor, it’s usually used in electrode materials, transparent conducting materials, gas-sensing materials, pressure-sensitive materials and so on, but used less in thermoelectric field. In this paper, the thermoelectric effect, the development, application and classification of thermoelectric materials were discussed. The usual preparation methods of thermoelectric ceramics and thin films were introduced. The ways of how too improved the thermoelectric properties and the developmental orientation of thermoelectric materials were also described.The pure SnO2 samples were used as contrast. Fe(NO3)3·9H2O, SnO2 and PVA were used as raw materials, Fe-doped SnO2 powder precursor were prepared by PVA powder composite method, and the Fe-doped SnO2 ceramics target material were synthesized by solid reaction process. The sintering temperature, heat retaining time and doping level were 1300-1500℃,8-12h and 0-20at%, respectively. One of these conditions was changed when other conditions were the same, and the XRD, metallography, SEM and frequency characteristics of resistance test were used, in order to investigate the influence of sintering temperature, heat retaining time and doping level to the sintering properties of SnO2 ceramics. The best preparation condition of ceramics were selected. To pure SnO2.the best preparation condition were sintering to 1450℃and retain heat for 10h. The best preparation condition of Fe-doped SnO2 were 1350℃sintering temperature and 10h heat preservation time. The phase and microstructure of the samples were attributed by XRD, metallographical and SEM, in order to investigate the influence of sintering temperature, heat preservation time and doping level on sinterability. The result shows that the samples were single phase at the best synthesis condition, the grain size was well-distributed and the crystallization quality was good. The grain size of pure SnO2 was small and growing bigger clearly after Fe doped. With the rise of sintering temperature and the increase of Fe doping level, the trend of grain size was upwards obviously. But the exorbitant sintering temperature and doping level would lead to overgrowth of grain, debasement of crystallization quality and the enrichment of Fe2O3 impurity phase at grain boundary.The Fe-doped SnO2 targets prepared by solid state reaction were used as target to deposit Fe-doped SnO2 thin film at Al2O3(0001) substrate by pulsed laser deposition technique, at different oxygen pressure, substrate temperature and doping level. The influence of these deposition conditions on deposition quality of thin films were studied by XRD. The optimized deposition conditions of thin films are 650℃substrate temperature, 4Pa oxygen pressure,8 minutes deposition time and 280mj laser energy. The thin films of different Fe doping levels were also analyzed, the result show that the doping of Fe would help improve the deposition quality of thin films.The preparation of Co doped SnO2 ceramics were also explored. The result shows that plenty of Co2SnO4 were formed, especially when the doping level was higher than 6at%. The rise of sintering temperature would not make the quantity of Co2SnO4 decrease but make the sinterability poorer. The result of frequency characteristics of resistance test shows that the cobalt was more effective in improving the electrical properties than iron.

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