Structural and thermodynamic properties of (Cu,Ni)-(In,Sn,Sb) binary and higher-order compounds for lead-free soldering alloys: Ab initio database, correlations for cohesive properties and microscopic interpretation of the bonding trends

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

Saint-Malo

Conferencia; CALPHAD XLVI Conference; 2017

The French National Center for Scientific Research

The present work offers a progress report of along-term research line aimed at: (i) developing a complete database withstructural, thermodynamic, cohesive and elastic properties of the intermetalliccompounds (ICs) of interest in the design of new lead-free soldering (LFS)alloys; and, (ii) establishing correlations between these properties and theelectronic structure. Specifically, a systematic and comparative study of thestructural,  cohesive and electronicproperties of a large number of MeaXb type ICs (withMe=Cu,Ni and X=In,Sn,Sb) reported as stable or metastable, as well as varioushypothetical compounds involved in the thermodynamic modeling using theCompound-Energy Formalism, is presented. The work relies upon an extensivedatabase with total-energy versus volume information obtained usingdensity-functional-theory (DFT) projected augmented waves (PAW) calculationsimplemented in the Vienna Ab Initio Simulation Package (VASP). It is shown thatthe volume (Vo), bulk modulus (Bo) and cohesive energy (Ecoh)of these ICs can be accurately studied as functions of the Average Group Number(AGN), i.e., the weighted average of the number of valence electrons involvedin the VASP calculations. Moreover, the Cohesive Energy Density, defined as Ecoh/Vo,is shown to correlate very well with the AGN variable and with Bo.In addition, various correlations involving the cohesion-related quantities (Bo/Vo)½and (Ecoh½/Vo) and the AGN are compared indetail with related relations involving the Miedema empirical electron densityat the boundary of the Wigner?Seitz cell. These striking regularities are givena microscopic interpretation based on the evolution of the contributions of thed- and p-electrons to their electronic Density of States. In particular,the effects upon cohesion of the hybridization of d- and p-electrons, andthe filling up of bonding and anti-bonding states are highlighted.