Electrical and thermoelectric properties of nanocrystal substitutional semiconductor alloys Mg3(BixSb1−x)2prepared by mechanical alloying

Nanocrystal substitutional semiconductor alloys Mg 3 (Bi x Sb 1− x ) 2 (nano-Mg 3 (Bi x Sb 1− x ) 2 ) with a mean grain size of ∼30 nm were prepared by mechanical alloying plus hot-pressing, and their dc electrical and thermoelectric properties were investigated from room temperature down to 20 K. The results indicated that lattice parameters a and c of nano-Mg 3 (Bi x Sb 1− x ) 2 increased linearly with increasing Bi content x , in agreement with Vegard's law. The dc resistivity ρ of nano-Mg 3 (Bi x Sb 1− x ) 2 decreased monotonically with increasing x , and a drop of over five orders of magnitude was reached at 300 K when x increased from 0 to 1. Moreover, the temperature behaviour of the resistivity of nano-Mg 3 (Bi x Sb 1− x ) 2 changed sensitively with x , and a transition from the semiconducting state (i.e. dρ/d T < 0) to the metallic state (dρ/d T > 0) occurred between x = 0.7 and 0.8. Meanwhile, this transition was verified by the measurements of the temperature behaviour of the Seebeck coefficient S of nano-Mg 3 (Bi 1− x Sb x ) 2 with different x . In addition, Mott's ρ ∝ T −1/4 law was observed at lower temperature regimes for the nano-Mg 3 (Bi x Sb 1− x ) 2 ( x ≠ 0), suggesting the occurrence of hopping conduction. Although experiments showed that the Seebeck coefficient of nano-Mg 3 (Bi 1− x Sb x ) 2 decreased monotonically with x , their thermoelectric power factors PF changed non-monotonically, and a maximum PF of 1.4 µW cm −1 K −2 was achieved at room temperature for x = ∼0.8, which was more than three orders magnitude greater than that of monolithic Mg 3 Sb 2 .