Texture control of bulk mechanical alloyed Bi-Te thermoelectric materials via shear extrusion

Shear extrusion processing with combination of bulk mechanical alloying (BMA) is employed to yield the p-type (Bi₂Te_3)0.2(Sb ₂Te_3)0.8 and n-type (Bi₂Se _3)0.05(Bi₂Te_3)0.95 Bi-Te thermoelectric materials from elemental granules. The shear-extruded p-type, n-type Bi-Te compounds have the preferred orientation factor (F) to anisotropic crystallographic structure : F_P(max)= 0.63, F_n(max)= 0.67. For p-type, in case of the single crystal, F = 1.0 and p _min = 0.995x10^-5 Ωm. On the contrary, hot pressed sample has F = 0.02 and p = p _random = 2.110xl0^-5 Ω m. In case of the shear extruded sample, 0.5<F<0.63. This high F value assures that the measured resistivity becomes nearly equal to lxlO^-5 Ωm, the resistivity for the single crystals with F = 1. Maximum power factors of p-type, n-type materials are achieved to 4.33xl0^-3(W/mK²), 3.31xl0^-3(W/mK²) even without any dopants. The bending strength of the material produced is also improved to be the range of 120-160MPa, six times larger than that for zone-melted specimen.