Thermoelectric Material Design in Pseudo Binary Systems of Mg_2Si - Mg_2Ge - Mg_2Sn on the Powder Metallurgy Route

摘要

Fundamental studies on the thermoelectricity have been mainly done in the pseudo binary systems of Mg_2Si - Mg_2Ge - Mg_2Sn. In recent years, their thermoelectricity is revisited because of light-weight, low initial const and short turning back time in addition to high potential in figure-of-merit for ZT approaching to unity or more. Conventional melting and solidification, or, normal PM routes fail in precise, wide-range control of chemical composition and microstructure control. New PM route via bulk mechanical alloying is developed to fabricate the solid solution semi-conductive materials with Mg_2Si_(1-x)Ge_x and Mg_2Si_(1-y)Sn_y for 0 < x, y < 1 and to investigate their thermoelectric materials. Since Mg_2Si is n-type and both Mg_2Ge and Mg_2Sn are p-type, pn-transition takes place at the specified range of germanium content, x, and tin content, y. Through optimization of chemical composition, solid-solution type thermoelectric semi-conductive materials are designed both for n- and p-type materials. In addition, appropriate doping condition can be searched in the specified range of x and y.