EXPERIMENTAL STUDY AND THERMODYNAMIC RE-ASSESSMENT OF THE CO-SB SYSTEM

• Published in: Calphad Vol. 73; p. 26
• Main Authors: Broz, P, Zelenka, F, Vfestal, J, ZemanovS, A, Bursfk, J, Svoboda, M, Kroupa, A
• Format: Journal Article
• Language: English
• Published: Elmsford Elsevier BV 01.06.2021
• Subjects: Binary system; Binary systems; Differential thermal analysis; Eutectic reactions; Liquidus; Phase diagrams; Phase equilibria; Phase stability; Scanning electron microscopy; Thermoelectric materials
• ISSN: 0364-5916; 1873-2984

The Co-Sb system is of a keen interest because of the existence of CoSb3 phase with skutterudite structure, which is the basis for doped CoSb3 based skutterudite thermoelectric materials. A good knowledge on phase relations in this binary system, including especially the CoSb3 phase, is therefore crucial for the study of the thermal and phase stability of the doped analogues. This system has been studied experimentally and theoretically by many authors. Compared to other studies, the recent thermodynamic assessment published by Zhang et al. [1], leading to phase diagram shown in Figure 1, may not be necessarily fully correct as pointed out in a critical review by Okamoto [2], A contradiction exists especially in the position of the liquidus line on the Sb-rich side of the phase diagram and for the eutectic reaction, liquid ↔ CoSb3 + Sb, the information on which can be found in Massalski [3]. Correct information on the phase equilibria in this part of the phase diagram is necessary for prediction of phase stability of the thermoelectric phase in higher order systems. To obtain reliable data, experimental alloys in composition range from 80 to 100 at% Sb were prepared and investigated by differential thermal analysis (DTA) on a Netzsch STA 409 CD/3/403/5/G apparatus and by methods of phase analysis performed on a Tescan LYRA 3XMU FEG/SEM scanning electron microscope (SEM) with an XMAX 80 energy dispersive X-ray (EDX) analyzer by Oxford Instruments. The data were compared with existing literature information and thermodynamic re-assessment of this binary system based on CALPHAD approach, using software PANDAT and ThermoCalc, was done. The work has been financially supported by the Czech Science Foundation under the project GA 17-12844S and by the project bibCEITEC_2020 CEITEC 2020 (LQ1601) from the Ministry of Education, Youth and Sports of the Czech Republic under National Sustainability Programme II.