Research On Thermoelectric Properties Of B₄C-based Materials

Thermoelectric materials play an important role in solving the energy andenvironment problems, and B4C-based materials are considered to be one of themost potential high temperature thermoelectric materials. At present, the mainmethod of preparing boron carbide is arc smelting which has some disadvantagesincluding high temperature (more than2350℃) and large gain size of the specimens.In order to improve the thermoelectric performance of the material, the hot pressingis used to prepare the B4C-based composite which were added some other materials.Firstly, SiC/B4C composites with different composite were prepared by hotpressing. There are not obvious crack appeared between the second phase andmatrix. The conductivity of the composite decline obviously with the doping of SiC,and the thermal conductivity increase obviously at the same time. The seebeckcoefficient of the composite is positive, which means it is p-type thermoelectricmaterials. When doping amount is30wt%, the seebeck coefficient increases a littlebecause the increase of the dislocation. Seebeck coefficient of the composite inwhich SiC content is50wt%and70wt%declined. The seebeck coefficient of thethree kinds of composite material increased greatly with the increase of thetemperature. The thermoelectric figure of merit decreased with the doping of SiC.TiB2/B4C composite material was prepared to improve the electrical performanceof the material. The conductivity of the material increased by2~3orders ofmagnitude in room temperature, and1~2orders of magnitude in high temperature.Thermal conductivity increased greatly and seebeck coefficient appear larger reduceat the same time. The type of the (B4C+25.4vol%TiB2) material changed fromp-type to n-type which provides a new idea to prepare the n-type B4C thermoelectricmaterials. The experimental results show that, the power factor and pyroelectricmerit both reduce in the material which added12.4vol%TiB2. In the material whichadded12.4vol%TiB2, the power factor increase largely and the dimensionlesspyroelectric merit is0.5times larger than the undoped material.At last, the B4C bulk was prepared by spark plasma sintering and find that thematerial which doped1.2at%Si with better conductivity and lager seebeckcoefficient. The electric properties will degrade if the composite contains too muchSi.