Influence of structures and compositions on thermoelectric properties of silicon borides

Abstract

Silicon borides have excellent potential as high-temperature thermoelectric devices because of their high melting point and relatively large Seebeck coefficient. In the present work, the silicon borides were prepared by CVD, a melting and a sintering method. CVD was used for preparing samples to measure the intrinsic characteristics of the silicon borides. On the other hand, a melting and a sintering method were used for adding some elements (Fe, Cr, Co, Ni) to the silicon borides. CVD was attempted by high-frequency (80kHz) induction heating, and the samples were deposited on graphite substrates at the substrate temperatures from 1188 to 1616 K under the total pressures in the CVD chamber of 2.7 kPa. Sintered samples were prepared by a pressing from powder raw materials, and the pressed pellets were sintered at 1723 K for 2 hours in an electric furnace. The crystal structures of the samples were characterized by X-ray diffraction (XRD), and the morphologies were observed by scanning electron microscope (SEM). Electrical properties such as Seebeck coefficient, electrical conductivity and Hall effect were measured. The Seebeck coefficient of the boride reached about 400 /spl mu/VK/sup -1/, and the electrical conductivity was above 30000 Sm/sup -1/. The values of carrier mobility were less than 0.1 cm/sup -2/V/sup -1/s/sup -1/.