Structural and thermodynamics effects of incorporating In atoms into the (mC44) Cu6Sn5-type structure phase: ab initio study, correlations and chemical-bonding trends

N. V. GONZÁLEZ LEMUS; S. B. RAMOS; G.F. CABEZA; C. DELUQUE TORO; A. FERNÁNDEZ GUILLERMET

Santos

Congreso; Thermodynamics Of Alloys, TOFA 2016; 2016

The University of São Paulo - School of Engineering

A long-standing challenge of the physical chemistry of materials is the accurate account of the composition dependence of theoretically and practically relevant properties for various classes of compounds. Since a complete experimental characterization is usually produced only for some selected compositions and temperatures, there has been considerable interest in the design and testing of predictive methods to extend the database on metallic alloys and compounds. Previous work by us has been devoted to the application of ab initio calculation methods in producing, systematizing and interpreting new information to characterizestable and metastable intermetallic phases (IPs) of the Cu-In, Cu-Sn, Ni-In and Ni-Sn systems [1,2]; these being systems of potentially interest in connection to lead-free soldering applications. An ab initio database including information such as lattice-parameters, cell volume, bulk modulus and other equation-of-state (EOS) parameters, the energy of formation from the elements and the electronic structure has been reportedby us for relevant IPs of these systems. The present work goes one step forward in this line of research by focusing on the eta phase of the ternary Cu-In-Sn compound. Considerable effort has been devoted to the characterization of this phase, since it is one of the technologically relevant phases detected at the joint in diffusion couples [3]. The eta phase is a common equilibrium phase of both the Cu?In (Cu2In of unknown structure) and Cu?Sn (Cu6Sn5-mC44) binary subsystems of the Cu?In?Sn system. The Cu2In and Cu6Sn5phases have been proposed to form a continuous solid solution in the ternary phase diagram between 186 °C and 383°C, although no further details are given about the ternary eta phase [4]. Moreover, it was reported that most of the ternary IPs occurring at the interconnection zone in Cu/In?Sn/Cu joints are those formed by incorporating In or Sn to the binary compounds stable in the subsystems Cu?Sn and Cu?In, respectively [3].Based on these facts, in the present work, we are interested in considering the effects of incorporating In atoms into the known eta structure of the Cu-Sn intermetallic, viz., (mC44) Cu6Sn5-type phase. The purpose of the work is, in the first place, to establish the energetically favorable way in which In atoms can replace the Sn atoms in the binary compound. To this aim we use ab initio projected augmented waves (PAW) calculations using the VASP code to study the energy of formation and cohesive energy of the compounds generated by progressively filling up with In the sublattices originally occupied by Sn atoms in the (mC44) Cu6Sn5 phase. In the second place, we aim at studying the effects of the In concentration upon the structural and EOS parameters of the Cu6 (Sn,In)5 phase. The composition dependence of these calculated properties will be compared with the experimental data available and with previous theoretical results from the literature. Finally, we aim at interpreting the theoretical trends by establishing the composition dependence of the electronic structure and discussing that in the light of current theories of p-d bonded intermetallic phases. [1] S. Ramos de Debiaggi, C. Deluque Toro, G.Cabeza, A. Fernández Guillermet, J. Alloy. Compd. 542 (2012) 280?292. [2] S. Ramos de Debiaggi, C. Deluque Toro, G.F. Cabeza, A. Fernández Guillermet, J. Alloy. Compd. 576 (2013) 302?316. [3] S.A. Sommadossi, A. Fernandez Guillermet, Intermetallics 15 (2007) 912?917. [4] W. Köster, T. Gödecke, D. Heine, Z. Metallkd. 63 (1972) 802?807.