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UCTION

THERMOELECTRIC materials and devices have been the subject of intensive study, primarily because of their various niche applications in the direct energy conversion between heat and electricity without the need for moving parts, and the world’s strive to meet sustainable energy demands.[1–16] Numerous types of thermoelectric materials have been proposed, including Ag-Sn-Te, Ag-Sn-Sb-Te, Pb-Sb-Ag-Sn-Te, Ag-Pb-SnIn-Te, and Bi-Sb-Ag-Sn-Te alloys.[10–16] Knowledge of the Ag-Sn-Te system is fundamentally important, since it is the basic ternary system for all the thermoelectric materials mentioned above. The microstructures and phases of materials are crucial to their thermoelectric properties.[1–16] However, there are only a few phase-related studies of the Ag-SnTe ternary system.[17–21] Hahn and Schulze[17] and Blachnik et al.[18] reported the formation of an incongruently melting ternary AgSnTe2 compound. A simple eutectic type Ag2Te-SnTe quasi-binary phase diagram and the liquidus projection of the ternary Ag-Sn-Te JUI-SHEN CHANG, Doctoral Student, SINN-WEN CHEN, Professor, and KUO-CHUN CHIU, Master Student, are with the Department of Chemical Engineering, National Tsing Hua University, #101, Sec. 2, Kuang-Fu Road, Hsin-Chu 300, Taiwan R.O.C. Contact e-mail: [email protected] HSIN-JAY WU, formerly Postdoctoral Researcher with the Department of Chemical Engineering, National Tsing Hua University, is now Assistant Professor with the Department of Materials and Optoelectronic Science, National Sun Yat-Sen University, Kaohsiung, Taiwan R.O.C. JEE-JAY CHEN, formerly Undergraduate Student with the Department of Chemical Engineering, National Tsing Hua University, is now Doctoral Student with the Department of Chemical Engineering, University of Michigan, Ann Arbor, MI. Manuscript submitted June 28, 2013. Article published online April 30, 2014 3728—VOLUME 45A, AUGUST 2014

system were determined by Blachnik et al.[18,19] The structure and properties of the Ag2SnTe3 compound were determined by de Chalbaud et al.[21] Romermann and Blachnik[22] determined the excess enthalpies of Ag0.5Sn0.5Te. A liquidus projection gives information about the primary solidification phases and the invariant reactions. It is very useful for the illustrating of the solidification behavior of alloys and the phase formation during solidification.[23–26] Moreover, it is also valuable for developing alloys and in determining processing routes. This study determines the liquidus projection of the Ag-Sn-Te system, because only one preliminary study[18,20] has been conducted and there is a need for verification. Furthermore, the phase equilibria of the three constituent binary systems have been updated[27–32] and modification of the proposed liquidus projection[18,20] is required.

II.

EXPERIMENTAL PROCEDURES

Proper amounts of pure Ag shots (99.9 wt pct, Alfa Aesar), Sn shots (99.9 wt pct, SHOWA), and Te flakes (99.9wt pct, Alfa Aesar) with a total weight of 1 g were weighed and encapsulated in a quartz tube in a 2 9 10 5 bar vacuum. The sample