Ab initio study of Cu-In-Sn and Ni-In-Sn intermetallics: Systematics and correlations in the cohesive and electronic properties

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

La Plata

Workshop; VI Workshop on Novel Methods for Electronic Structure Calculations.; 2015

Departamento de Electrotecnia - Universidad Nacional de La Plata

Thethermophysical properties of intermetallic phases (IPs) of the Cu-In-Sn and Ni-In-Snsystems are of current interest in relation to the design of lead-freesoldering (LFS) technologies. Considerable efforts have been devoted to thedevelopment and application of predictive approaches to describe thethermodynamics of binary and higher order IPs of actual and potentialtechnological relevance for the lead-free soldering methods. In this work our researchadvances towards the characterization and understanding of cohesion and bondingproperties in these type of systems are described. A systematic and comparativeab initio density functional theory(DFT) study of a large group of stable, metastable and hypothetical IPs of thebinary Me-X (Me = Cu,Ni; X = In,Sn) subsystems, is presented. Hypotheticalcompounds, for which experimental data is usually not available, are involvedin the thermodynamic CALPHAD type modeling of the phase diagrams of thesesystems; the ab initio methods can be of great use to provide useful input datafor these modeling methods. For all the set of Me-X IPs considered, thecomposition and volume dependence of their bulk modulus (Bo) andcohesive energies (Ecoh) are discussed, as well as the systematiceffects of replacing Cu by Ni in these IPs.  New correlations between cohesion-relatedquantities such as (Bo/Vo)½ and (Ecoh½/Vo)with the number of valence electrons per unit volume, are established and comparedwith similar Miedema´s empirical relations. For theNi3In-hP8 and Ni3In-cP4 phases, whichcompete in stability, also their elastic constants and averaged elasticmoduli are calculated; and based on these results predictions are made for themechanical properties of this compound. The composition and structuredependence of the cohesion for this class of compounds is analyzed in terms ofa theoretical view that involves the hybridization of the d-states of Cu or Ni with the sand p-states of In or Sn. Acomparative analysis is performed of the density of states (DOS) of variousrepresentative, iso-structural Me-X compounds. Various effects of relevance tounderstand the consequences of replacing Cu by Ni in LFS alloys are highlightedand explained microscopically. In addition to the reported thermodynamicinformation, which can be of direct use as input in the CALPHAD optimizations,the picture of the variations in cohesive properties emerging from the presentwork should be useful in systematizing the thermophysical and structuraldatabase for this class of compounds. Finally, by considering specific ternary IPs of the Cu-In-Sn and theCu-In-Sb related system, the problem of the design of structural models basedon sublattice schemes is discussed