Thermophysical systematics of Ni3In and Ni3Sn compounds: Ab initio database and interrelations

BERTOLDI, DALÍA S.; RAMOS, SUSANA B.; FERNÁNDEZ GUILLERMET, A.

CALPHAD-COMPUTER COUPLING OF PHASE DIAGRAMS AND THERMOCHEMISTRY

PERGAMON-ELSEVIER SCIENCE LTD

Año: 2020 vol. 71 p. 1 - 9

0364-5916

The subject of the paper is the use of density-functional-theory methods to determine the zero-kelvin cohesive and elastic properties, as well as the vibrational contribution to the thermal properties of the Ni3X (X = In,Sn) compounds, which are interesting in the field of lead-free soldering materials. The phases are stable at low temperatures in the DO19 (hP8) structure, and at high pressures in the cubic L12 (cP4) structure. In the current work, the T = 0 K energy-volume relations given by the VASP are combined with phonon calculations using the PHONOPY code to develop a quasi-harmonic-approximation account of the vibrational contribution to the thermal properties. The resulting ab initio database is used to: i) analyze trends in the composition dependence of the cohesive energy, the bulk modulus, the elastic constants, the engineering elastic moduli and three Debye temperatures; ii) test some rather general, as well as various material-dependent correlations between these properties; and, iii) test with the present compounds the theory-based interrelations between cohesive and vibrational properties previously established in studies of the transition metals and of a large class of related Cu-X and Ni-X (X = In,Sn) compounds. In particular, the cohesive energy of the present elements and compounds is shown to correlate with an entropy-based characteristic energy, and with the vibrational contribution to the thermal expansion coefficient evaluated at the Einstein temperature.