Solid-State Synthesis of Mg₂X (X=Si, Ge, Sn and Pb) via Bulk Mechanical Alloying

Abstract

Magnesium base alloys and compounds are attractive for various applications as a functional material. In particular, a series of binary system by Mg2X (X = Si, Ge, Sn and Pb) has fascinated many researchers and engineers by its thermoelectric properties and semi-conductive performance. Many barriers in its processing rejects precise investigation of these types of semiconductive compounds: high vaporizing pressure and mechanical adhesion of magnesium, reaction of germanium and tin with crucibles, and, difference of melting point among elements, X. Solidstate processing via the bulk mechanical alloying enables us to directly fabricate these Mg2X semiconductive materials in high density performs. The precise control of chemical composition leads to an investigation on the dilution and enrichment of X in Mg2X. Two types of solid-state reactivity are introduced: e.g. synthesis of Mg2Si from an elemental mixture Mg – Si, which is a nucleationcontrolled process, while synthesis of Mg2Sn from Mg – Sn is a diffusion-controlled process. The thermoelectricity of these Mg2X is evaluated for discussion on the validity and effectiveness of this new PM route as a reliable tool for fabrication of thermoelectric compounds.

Microstructure and Thermoelectric Properties of n- and p-Type Doped Mg2Sn Compounds Prepared by the Modified Bridgman Method

“…Methods of direct co-melting, 9-11 mechanical alloying, 12-14 solid-state reaction, [15][16][17] and spark plasma sintering [18][19][20] have been used to prepare Mg 2 X (X = Si, Ge, Sn) compounds and their solid solutions. Among these reported results, the method of direct co-melting followed by lengthy annealing used by Zaitsev et al 8 showed the highest ZT values achieved to date.…”

Semi-Solid Preparation and Performance of Magnesium Based Thermoelectric Materials

“…Practical applications generally require zT > 1. From this equation, it may be seen that in order to obtain a high figure of merit zT, a large Seebeck coefficient, a large electrical conductivity and a low thermal conductivity are required [10][11][12]. Mg 2 Si 0.4 Sn 0.6 was proved to have high thermoelectric properties.…”