Cristallographic anisotropy control of n-type Bi-Te-Se thermoelectric materials via bulk mechanical alloying and shear extrusion

The shear extrusion processing combined with bulk mechanical alloying is proposed to yield the n-type Bi-Te-Se material from elemental granules. It has well-developed texture so as to improve the electric conductivity and thermoelectric properties. The shear extrusion processing of (Bi ₂Se₃)_0.05(Bi₂Te₃) _0.95 alloy green compact can afford the preferred orientation factor of anisotropic crystallographic structure: F = 0.67. The electric resistivity of (Bi₂Se₃)_0.05(Bi₂Te ₃)_0.95 is controlled to be 0.491 × 10^-5 (Ωm), which is 0.2 times lower than that of hot-pressed specimen. Maximum power factor is achieved to be 3.31 × 10^-3 (W/mK²) even without any dopants. The bending strength of the material produced in this work is also improved to be 166 MPa, 1.7 times higher than that of conventional hot-extruded specimens.