Control of grain size and crystal orientation for Bi-Sb-Te compounds

Reducing the grain size of Bi/sub 0.5/Sb/sub 1.5/Te/sub 3/ was attempted by mechanical alloying under ultra low oxygen atmosphere. The powder prepared by mechanical alloying was sintered by hot pressing at 650 K under an atmosphere of 4% H/sub 2/ with Ar balance (0.1 MPa). The crystal orientation in the sintered block was random. Then the block was deformed by ultra high pressure hot pressing at 650 K or 700 K or 750 K to obtain a desirable orientation for thermoelectric properties. Improvement of the crystal orientation in the deformed specimens was not confirmed by TEM. The results of electrical resistivity and Hall coefficient measurements, however, revealed that better orientation was indicated in the electrical properties.