Enhanced thermoelectric performance of Mg2Si0.4Sn0.6 solid solutions by in nanostructures and minute Bi-doping

Abstract

n-type Mg2(Si0.4Sn0.6)Bix (0 ≤ x ≤ 0.04) solid solutions with minute amounts of Bi were prepared by induction melting, melt spinning (MS), and spark plasma sintering (SPS) method, namely the non-equilibrium technique MS-SPS, using bulks of Mg, Si, Sn, Bi as raw materials; the phase components, microstructures as well as the thermoelectric properties were systematically investigated. The multiple localized nanostructures within the matrix containing nanoscale precipitates and mesoscale grains were formed, resulting in remarkably decreasing of lattice thermal conductivities, particularly for samples with the nanoscale precipitates having the size of 10–20 nm. Meanwhile, the electrical resistivity was reduced and the Seebeck coefficient was increased by Bi-doping, causing improved electrical performance for the Mg2(Si0.4Sn0.6)Bix (0 ≤ x ≤ 0.04) compounds. The dimensionless figure of merit ZT was significantly improved and the maximum value reaches 1.20 at 573 K for the Mg2(Si0.4Sn0.6)Bi0.03 sample, greatly higher than that of the non-doped samples.

Improvement of Thermoelectric Properties Via Combination of Nanostructurization and Elemental Doping

“…41 With the increase of x, the carrier concentration first increases rapidly and peaks at 2.932 9 10 20 cm À3 when x is 0.03, and then it drops down to 2.282 9 10 19 cm À3 when x is 0.04 (Table I), as reflected in a corresponding change in electrical conductivity. 41 The electrons introduced by Bi atoms are responsible for the increase of carrier concentration. [42][43][44][45][46] However, according to the Bi-Mg phase diagram, 47 the excessive Bi atoms may react with Mg atoms to form p-type Mg 3 Bi 2 .…”

“…41 The XRD results identified the formation of single-phase solid solutions in Mg 2 (Si 0.4 Sn 0.6 )Bi x because the peaks of all specimens are located between Mg 2 Si and Mg 2 Sn phase and a positive linear correlation is obtained between the lattice parameter and the amount of Bi. 41 …”

“…1. 41 By taking a selected-area electron diffraction (SAED), two uniform sets of SAED patterns along [111] axis of Mg 2 Si for the host and the nanoprecipitate were obtained (Fig. 1b inset), revealing the same structure and complete crystallographic alignment of the host and nanoprecipitate.…”

Electronic Structure and Thermoelectric Properties of Pseudoquaternary $$\hbox{Mg}_{2}\hbox{Si}_{1-x-y}\hbox{Sn}_{x}\hbox{Ge}_{y}$$ Mg 2 Si 1 - x - y Sn x Ge y -Based Materials

“…In the case of the Bi-doped system, our analysis was based on the KKR-CPA electronic band structure calculated for Mg 2 …”

“…Mg 2 Si 1Àx Sn x has been found to be the most favorable in terms of thermoelectric energy conversion, as it has the highest thermal resistivity due to the maximum mass difference between its components. [1][2][3] However, quasiternary solid solutions Mg 2 Si 1ÀxÀy Sn y Ge z have attracted much less attention. Very recently, a high figure of merit ZT % 1.4 was measured in the Bi-doped Mg 2 Si 1ÀxÀy Sn y Ge z system.…”