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

Nanocrystal substitutional semiconductor alloys Mg-3(BixSb1-x)(2) (nano-Mg-3(BixSb1-x)(2)) with a mean grain size of similar to 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(BixSb1-x)(2) increased linearly with increasing Bi content x, in agreement with Vegard's law. The dc resistivity rho of nano-Mg-3(BixSb1-x)(2) decreased monotonically with increasing x, and a drop of over five orders of magnitude was reached at 300K when x increased from 0 to 1. Moreover, the temperature behaviour of the resistivity of nano- Mg-3(BixSb1-x)(2) changed sensitively with x, and a transition from the semiconducting state (i.e. d rho/dT < 0) to the metallic state (d rho/dT > 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(Bi1-xSbx)(2) with different x. In addition, Mott's rho proportional to T-1/4 law was observed at lower temperature regimes for the nano-Mg-3(BixSb1-x)(2) ( x not equal 0), suggesting the occurrence of hopping conduction. Although experiments showed that the Seebeck coefficient of nano-Mg-3(Bi1-xSbx)(2) decreased monotonically with x, their thermoelectric power factors PF changed non-monotonically, and a maximum PF of 1.4 mu W cm(-1) K-2 was achieved at room temperature for x = similar to 0.8, which was more than three orders magnitude greater than that of monolithic Mg3Sb2.