Bi Co-based Oxide Thermoelectric Ceramics And Thin Films And Performance

Thermoelectric materials were the functional materials that could convert heat energy to electric energy directly due to thermoelectric effects and had immense prospects with many applications in thermoelectric power enervation and refrigeration. The new Cobalt oxide thermoelectric material had high electric-conduction meritσand seebeck coefficient. Thus, it had attracted many people. At present, the research of Bismuth Cobalt oxide thermoelectric material mainly focus on the preparation and property of it, the study of low-dimension material become popular in the near future. This paper discussed the structural and thermoelectric properties of cobalt oxides system thermoelectric materials, introduced various method of preparing thermoelectric ceramics and thermoelectric films, reviewed the ways of how to improve thermoelectric performances. Application of thermoelectric materials on thermoelectric power generation and cooling was investigated.This paper study on the preparition of Bi2Sr2Co2Oy ceramic and films, then research their property of electrical. The main works are as following:Polycrystalline sample of Bi2Sr2Co2Oy was prepared by solid state reactions of Bi2O3,SrCO3 and CO2O3. The best methodology was:pre-calcine:overheating to 860℃withing 2h, heating preservation 6h; second calcine:overheating to 880℃withing 2.5h, heating preservation 2h, then overheating to 890℃, heating preservation 4h, at last cooling to 880℃, heating preservation 2h. The phase and micro-organization of the ceramics were analyzed by XRD, SEM. The temperature dependence of the electrical resistivity was measured by a standard four probes method. The results showed that ceramics were single phase, layered grown obviously, organization was homogeneous, c-axis preferred orientation obviously. Notably semiconductor-metal transition existing in the Bi2Sr2Co2Oy ceramics which prepared by solid-state reactions.The target was Bi2Sr2Co2Oy polycrystalline which prepared by solid-state reactions. Bi2Sr2Co2Oy thin films were grown on Al2O3(0001) substrates by pulsed laser deposition(PLD) technique. Different annealing processes, that is, in situ annealing, post-annealing and non-annealing processes were investigated, and the last one was found to be the optimal preparation conditions. The best methodology was non-annealing: substrates temperature:790℃; oxgen pressure:60Pa; deposited times:8min; engery of pulsed laser:300mJ. X-ray diffraction showed that films were extension growth along c-axis. The temperature dependence of the electrical resistivity was measured by a standard four probes method, the result showed that films were semiconductor from 80K to 360K.Films with different deposited times were grown on 10°vicinal-cut and 15°vicinal-cut Al2O3(0001) substrates, testing the laser induced thermoelectric voltage(LITV) signals. LITV signals were first found in the Bi2Sr2Co2Oy thermoelectric films. The optimal deposited times was found both in 10°vicinal-cut and 15°vicinal-cut(deposited 6 min), at which the peak voltage of LITV signals reach 0.44V and 0.78V. In addition, the LITV signals of films grown on 15°vicinal-cut substrates were larger than LITV signals of films grown on 10°vicinal-cut substrates, that is LITV signals were proportional to vicinal-cut of substrates. The anisotropy of Seebeck coefficient lead to laser induced thermoelectric voltage(LITV)signals.