High Pressure And Temperature To Explore The Synthesis Of Beta-of Fesi <sub> 2 </ Sub> Thermoelectric Materials

The main job of this thesis is to use high purity Fe powder and Si powder according to the stoichiometric ratio mixed in domestic six sides, high temperature and high pressure on top pressure on synthesis. We get the following main conclusions:Under the condition of GPa pressure in 3.5 GPa and temperature to 800℃alloy is mainly composed of Si simple substance andε-FeSi,α-FeSi2 phase, on which this alloy fails to melt completely. Under the temperature between 825℃and 925℃, sample is mainly composed of theε-FeSi andα-FeSi2 phase, and silicon Si simple substance disappears. At the same time in silicon alloyεandαduplex can exist stably. When the temperature is more than 950℃alloy existsα-FeSi2 phase mostly, high temperature compound of the system is tetragonal phaseα-FeSi2; under the condition of high voltage solidification with the increase of pressure, according to different XRD samples of Fe -Si alloy are mostly the same and containε-FeSi,α-FeSi2 phase and during which other phase transition did not happen; along with the increase of synthesis time alloy is polluted. Hence according to the synthesis time, pressure, temperature,β-FeSi2 pyroelectricmaterial in six face top direct synthesis pressure apparatus can not be composed.Unadulteratedβ-FeSi2 belongs to P type semiconductor materials. Under different time of 800℃annealing treatment of block samples composed on the pressure apparatus of synthesisβ-FeSi2 phase samples are gotten finally. Different from the atmosphere, Fe-Si eutectic organization through high-pressure solidification is contracted into island shape after annealing treatment.From resistivity and seebeck coefficients of the synthetic samples doped with CO, through power factor show that thermoelectric performance of samples gotten at room temperature are not high, and the recent reports appeared in the literature showed thatβ-FeSi2 belongs to drier semiconductor thermoelectric materials, so the thermoelectric performance of samples in variable temperature is to be investigated in future work. But relative to undoped P typeβ-FeSi2 materials, seebeck coefficients is greatly improved, and resistivity is also decreased a lot. Synthetic samples doped with CO have already had the preliminary performance of thermoelectric material.