Journal of Alloys and Compounds 484 (2009) 172–176 Contents lists available at ScienceDirect Journal of Alloys and Compounds journal homepage: www.elsevier.com/locate/jallcom Thermodynamic description of the Cu–Sb binary system Wojciech Gierlotka ∗ , Dominika Jendrzejczyk-Handzlik Laboratory of Physical Chemistry and Electrochemistry, AGH University of Science and Technology, 30 Mickiewicza Av., 30-059 Krakow, Poland article info Article history: Received 28 March 2009 Received in revised form 30 April 2009 Accepted 12 May 2009 Available online 22 May 2009 Keywords: Cu Sb CALPHAD Phase diagram abstract The Cu–Sb binary system can be important for various applications, especially for electronic products as a part of lead-free soldering technology. It was found that  and  phases have been frequently encoun- tered in the electronic products. However, the two phases have been described as line compounds in the previous thermodynamic modeling, and their compositional homogeneities were not considered. Moreover, the  phase has been described as BCC A2 and this kind of description makes big problem for extension of calculations to some higher order systems. In this study, the thermodynamic properties of the Cu–Sb binary system were modeled and the phase diagram was calculated by the CALPHAD method, using experimental information reported in the literature. The  phase was described using compound energy model with two sublattices. In this way the compositional homogeneity could be calculated. Good agreement was found between the calculated results and the existing experimental data. © 2009 Elsevier B.V. All rights reserved. 1. Introduction The binary Cu–Sb system is the basis for various emerging Pb- free solders and for most of the important solder-related materials systems [1]. Moreover Cu and Sb are very important in microsol- dering alloys [2]. There are six intermetallic phases in the Cu–Sb system. Two of them, the  and  phases are observed in other solder-related systems, such as Sn–Sb–Cu, Sn–In–Cu systems [3,4]. The compositional homogeneity ranges of these two intermetallic compounds are significant in some of the Cu–Sn-based higher order systems [4,5]. Phase diagrams of multi-component systems are valuable tools for a basic understanding of materials processing and materials properties. However, thorough experimental determinations of the phase diagrams of multi-component systems are very costly and time-consuming. It is much more feasible to determine the phase diagrams with the CALPHAD approach [6]. In order to have good thermodynamic descriptions of the Cu–Sb-based multi-component systems, a precise description of the Cu–Sb binary system is nec- essary. The binary Cu–Sb system has been assessed by various investigators [2,7,8]. However, in the previous papers [2,7,8], the  phase was described using the line compound models with- out compositional homogeneity and  phase was modeled as a substitional solution. In this work the intermetallic compound is described as phase with the solubility range using compound ∗ Corresponding author. E-mail address: gilu@uci.agh.edu.pl (W. Gierlotka). energy model and  phase is modeled as DO 3 structure. Addi- tionally, based on Knoll and Steeb [9] work, liquid phase was also modeled as an associate liquid solution. 2. Thermodynamic description of the phases The following phases are considered in this work: FCC A1 (Cu), rhombohedral A7 (Sb), liquid, , , , ε, . Detailed information about these phases is given in Table 1 and below. 2.1. Substitutional solution—FCC A1 (Cu) The Gibbs free energy of pure elements as a temperature func- tion ◦ G i (T ) = G i (T ) - H SER i is represented by Eq. (1): ◦ G i (T ) = a + bT + cT ln (T ) + dT 2 + eT -1 + fT 3 + iT 4 + jT 7 + kT -9 (1) The ◦ G i (T) data are referred to the constant enthalpy value of the standard element reference H SER i at 298.15 K and 1 bar as recom- mended by Scientific Group Thermodata Europe (SGTE) [10]. The reference states are: FCC A1 (Cu) and rhombohedral A7 (Sb). The ◦ G i (T) expression may be given for several temperature ranges, where the coefficients a, b, c, d, e, f, i, j, k have different values. The ◦ G i (T) functions are taken from SGTE Unary (Pure elements) TDB v.4 [10]. Thermodynamic functions of pure elements are listed in Table 2. The FCC A1 phases is described by the regular solution 0925-8388/$ – see front matter © 2009 Elsevier B.V. All rights reserved. doi:10.1016/j.jallcom.2009.05.056