Thermoelectric Properties Of Polycrystalline Materials And Mechanics Behavior Analysis On Thermoelectric Devices

Thermoelectric (TE) materials are a class of functional materials that can convert thermal energy into electric energy, and also are the core parts of thermoelectric device which determine the work efficiency of the device directly. In practical applications, TE materials sometimes have to work in complicated physical field environments. And these environments will be in some extent the performance of TE materials, so as to change the conversion efficiency thermoelectric device. For TE device, mechanical stress caused by Heat bilges cold shrink is not be completely removed, so the work reliability cannot be ignored. This thesis is focusing TE materials and TE device, the research works are listed below:Firstly, based on the Boltzmann transport theory, form the point of view of the microstructure in polycrystalline TE materials, by introducing the transmission coefficient to simplify grain-boundary scattering effect, the electron distribution in the grains is analyzed to develop the theoretical models of TE properties of polycrystal TE materials under an external electric and magnetic fields. Then we learn the electric field effect of the Seebeck coefficient of polycrystalline bulk TE materials and the magnetic field effect of the Seebeck coefficient and the electrical conductivity of polycrystalline thin films. And then the influences of the grain size and the transmission coefficient on the TE properties of polycrystalline TE materials are studied. Furthermore, we study the interface effect of TE performance, by revealing the scattering mechanism of the transport electron. The influences of film-surface effect and grain-boundary effect on the electrical conductivity, as well as the contribution of those on the size effect are analyzed.Secondly, the effective stress distribution characteristic in the solder layer of the thermoelectric couple and the thermoelectric conversion efficiency of the segmented thermoelectric couple are investigated in this paper respectively. The simulation models of single-and double-segmented thermoelectric couple are built. Based on the commercial Software ANSYS, the effective stress distribution characteristics and the thermoelectric conversion efficiency of the two type thermoelectric couple and the hot side plate of them with different boundary conditions are studied respectively. The thermoelectric conversion efficiency of the segmented thermoelectric couple and the influence of different segment of thermoelectric couple legs on the thermoelectric conversion efficiency are also studied.In a word, in this thesis we study the electric and magnetic field effect of polycrystalline thermoelectric materials, the interface effect of polycrystalline thin films, and the work reliability of TE devices. All results are very useful on the development and applications of TE materials and devices.