Study On The Preparation And Properties Of Oxide Thermoelectric Materlas

Thermoelectric materials are semiconduting functional materials, which can be used to achieve a direct interconversion between thermal energy and electric energy by the movements of carriers. Thermoelectricity generation and cooling will be extensive applied in future. As the worldwide Environmental issues and the energy crisis Increasingly serious, The pressing pursuit for a new green environmental energy making thermoelectric materials a hot spot. Equipments using thermoelectric materials for power generation or refrigeration are characterized with quite a few merits, including compact structures, great reliability, noise-free operation, long operating life and non-pollution. Thus, they can be used in a great many fields, such as civil use, military, aerospace, etc. Oxide thermoelectric materials, with the advantages of low costs for raw materials, stability under high temperature and pollution-free, have become a relatively new research field. Hence, oxide thermoelectric materials, which are regarded as one of the few kinds of clean and green inexpensive thermoelectric materials for new energy, have a bright future in the daily life of mankind in the future. Designing and developing high performance thermoelectric materials have been a object for researcher. The performance of thermoelectric materials depends greatly on the dimensionless figure of merit ZT. The higher ZT value gives higher efficiency of energy conversion. ZT=S2σ/κ, where S,σ and κ, are Seebeck coefficient, electrical conductivity and thermal conductivity, respectively. The S2σ named power factor (PF), which is a judging parameter for thermoelectricity output power. Therefore, high performance thermoelectric materials need to have a high figure of merit, and a high power factor.In this thesis, environmental friendly oxide thermoelectric materials as the object are chosen to research. The thermoelectric properties of two typical oxides have done deep research. SrTiO3-based and ZnO-based thermoelectric materials are respectively prepared using conventional solid state reaction techniques. The microstructures of these thermoelectric materials are observed with XRD and SEM. The electrical resistivity and Seebeck coefficients are measured with self-made equipments. The main research contents of this thesis includes modifying the thermoelectric transport behavior by optimizing chemical composition and technological conditions, final improving the thermoelectric properties and searching for the physical mechanism of the electric heat transport for the oxide materials. Through these researches mentioned above, this thesis has achieved the following major innovations:1. The most appropriate sintering temperature of La doped SrTiO3has been studied, compared with the preparation environment of the air and argon, the reducing atmosphere to sinter of SrTiO3-based thermoelectric materials can reduce the sintering temperature, the energy consumption, and obtain higher thermoelectric figure of merit for the deficiency of oxygen. The results show that the most appropriate sintering temperature is1480℃, the power factor of sample sintered at1480℃Achieve21μWK-2at165℃.2. The thermoelectric performance of SrTiO3-based ceramics is effectively enhanced by dual doping of Rare Earth Element at A-site. It is found that the maximum power factor14μWK-2cm-1is obtained at the doping of La and Y. while dual doping of La and Nd, the maximum power factor14μWK-2cm-1is obtained at the amount of20%dopping content. The effect of Element Dy and Nb Dual dopping at both A and B site is not so significant as A-site dopping, the maximum power factor10μWK-2cm-1is obtained at the amount of10%dopping concentration.3. dual dopping effect of ZnO thermoelectric has been studied. Al, La co-doped ZnO and Al, Sn co-doped ZnO thermoelectric materials are respectively prepared using conventional solid state reaction techniques. It is found that the nano second phase affects the sample's electrical properties significantly. But consider the nano second phase can Significantly reduce the thermal conductivity of sample, the appear mechanism and effect has to be deeply studied.In this thesis, environmentally friendly oxide thermoelectric materials SrTiO3, and ZnO-based ceramics have been systematic investigated. The thermoelectric transportation is improved in different degrees by several methods, such as heavy elements doping, dual doping, nano-second phase, and optimization of preparation conditions. These research results show that oxide thermoelectric materials are great potentiality material system, and bear much research value and application prospects. Meanwhile, these results have provided useful theoretical and technological references for the research and development of oxide thermoelectric materials with high properties. As a result of time and length of this article, there is much work to be carried out in a deep-going way. However, it is believed that after the measures including, optimization of craftsmanship, changes of the controlling and regulating methods, larger breakthroughs will come up in the future for oxide thermoelectric materials.