Thermodynamic and mechanical properties of Ni3(In,Sn) DO19 compounds: ab initio ground state calculations and finite temperature effects

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

Montevideo

Congreso; QUITEL - 2nd Congress of Theoretical Chemists of Latin Expression; 2016

Universidad de la República and Instituto Pasteur de Montevideo

The Ni-In-Sn phase diagram hasbeen studied in connection to the development of lead free solders [1]. Most ofthe binary Ni-In and Ni-Sn compounds show significant solubility of the thirdelement (Sn or In). Also, there is a continuous intermetallic phase fieldconnecting the Ni3In and Ni3Sn intermetallic phases (IPs).These binary phases are very important; theyshare an ordered hexagonal DO19 type structure, have high meltingpoints and have been the subject of several studies due to their promisingmechanical properties. For the industrial applications of these materials, itis of interest to characterize their thermodynamic and mechanical properties.The purposes of the present work are, first, to test adensity-functional-theory (DFT) methodology to extend our previous 0 K abinitio study of the Ni3X (X = In,Sn) phases [2] to finite temperatures.Second, to characterize their elastic and mechanical properties. And third, tomodel an hypothetical ternary Ni3(In,Sn) compound to predict itscohesive, thermodynamic and elastic properties. The current Density Functional Theory(DFT) methodology makes use of the Vienna Ab-Initio Simulation Package (VASP) code[3]. Theelastic constants are calculated in the harmonic approximation (HA) and for thethermal properties we consider the HA and the quasi-harmonic (QHA)approximations. We evaluate the vibrational density of states,Gibbs free energies and entropies of formation, specific heats and thermalexpansion coefficients. We investigate the structural, elastic, thermal andmechanical stability properties of the DO19 Ni3In, Ni3SnIPs, the hypothetical ternary Ni3(In,Sn) compound, and thecorresponding pure elements: Ni, In, and Sn. Concerning the elastic properties, our calculatedresults for pure materials are found to agree with experiments and previously calculatedvalues. All the compounds here examined are found to be mechanical stable; theirelastic constants and polycrystalline averaged values for theelastic moduli lie in between those of the corresponding pure elements, with Nipresenting the highest values. The Ni3Sn compound is found to beharder the Ni3In one;while for the hypothetical Ni3(In,Sn) compound an intermediateelastic behavior within both binaries is predicted. According to the calculated ratio between the bulk and shear modulus (B/G), and alsothe Poisson´s ratio n, all the compounds can be classified as ductile.From the estimated Gibbs free energies of the compounds and pure elements, itis possible to conclude that at ambient temperature thermal effects would havea negligible contribution to their formation energies