RAMOS susana Beatriz
congresos y reuniones científicas
Thermodynamic and mechanical properties of Ni3(In,Sn) DO19 compounds: ab initio ground state calculations and finite temperature effects
Congreso; 42nd International Congress of Theoretical Chemists of Latin Expression - QUITEL 2016; 2016
Institución organizadora:
Universidad de la República
The Ni-In-Sn phase diagram has been studied in connection with the development of lead free solders [1]. Most of the binary subsystems Ni-In and Ni-Sn compounds show significant solubility of the third element (Sn or In). Also, there is a continuous intermetallic phase field connecting the Ni3In and Ni3Sn intermetallic phases (IPs). These binary phases are very important; they share an ordered hexagonal DO19 type structure, have high melting points and promising mechanical properties. From the point of view of the potential tecnological applications of these materials, it is interesting to characterize their thermodynamic and mechanical properties. The purposes of the present work are the following: i) test a density-functional-theory (DFT) methodology for extending our previous 0 K ab initio study of the Ni3X (X = In,Sn) phases [2] to finite temperatures; ii) characterize their elastic and mechanical properties; and, iii) model an hypothetical ternary Ni3(In,Sn) compound to predictits cohesive, thermodynamic and elastic properties. The current Density Functional Theory (DFT) methodology makes use of the Vienna Ab-Initio Simulation Package (VASP) [3]. The elastic constants are calculated in the harmonic approximation (HA) whereas the thermal properties are treated within both the HA and the quasi-harmonic (QHA) approximations. In this way we obtain the vibrational density of states, Gibbs energies and entropies of formation, specific heats and thermal expansion coefficients. With this information we investigate the structural, elastic, thermal and mechanical stability properties of the DO19 Ni3In, Ni3SnIPs, the hypothetical Ni3(In,Sn) compound. As a reference we also report the properties of the elements: Ni, In, and Sn. Our values for the elastic properties of the elemental solids are found to agree with experiments and previously reported ab initio values. All compounds studied here  are found to be mechanically stable, with their elastic constants and polycrystalline averaged values for the elastic moduli falling in between the values for the elements. Ni3Sn is found to be harder than Ni3In, whereas for the hypothetical Ni3(In,Sn) compound an intermediate elastic behavior within both binaries is predicted. According to the calculated ratio between the bulk and shear modulus (B/G), and the Poisson ratio mu, all the compounds can be classified as ductile. Finally, it is concluded that the effect of temperature upon the energy of formation of the present compounds would be negligible at room temperature.