Thermal properties and segregation phenomena in transition metals and alloys: modeling based on modified cohesive-energies

Abstract

In spite of free-atom electronic-relaxation contributions to transition-metal cohesive-energies, numerous studies have misused the latter instead of using the solid-state interatomic bondenergy in modeling bulk and surface properties. This work reveals that eliminating the free-atom contributions from experimental cohesive-energies leads to highly accurate linear correlations of the resultant bond-energies with melting temperatures and enthalpies, as well as with inverse thermal-expansion coefficients, specifically for the fcc transition-metals. Likewise, predictions of surface segregation phenomena in Cu-Pd and Au-Pd alloys on the basis of the modified energetics are in much better agreement with reported low-energy ion scattering spectroscopy (LEISS) experimental results, as compared to the use of cohesiveenergy values. A last demonstration of the problem and its solution involves the significant impact of the modification on segregation (separation) phase transitions in Cu-Ni model nanoparticles.

The Thermal Stability of Asymmetric Separated Configurations inside Alloy Nanoparticles: Atomic-Scale Modeling of Pd–Ir Nanophase Diagrams

“…The energy of Ising-like alloy atomic configuration is given by a sum over NN bonds characterized by energies w bulk A‑A , w bulk B–B , and w bulk A‑B . Corrected bond energies obtained by elimination of free-atom electronic-relaxation contributions from experimental cohesive energies , are w bulk Pd–Pd = −867 meV, w bulk Ir‑Ir = −1375 meV, and V chem = −37 meV (separation/demixing tendency) as obtained from DFT-computed mixing enthalpy . The Coordination dependence of near-surface Bond-Energy Variations (CBEV) was extracted from reported pure metal surface-energy anisotropy that was computed by DFT.…”

Vibrational and cohesive properties in 4d and 5d transition metals: systematics and interrelations

“…The cohesive and vibrational properties of transition metals and transition-metal compounds have been the subject of extensive experimental and theoretical studies in the last few decades [1][2][3][4][5][6][7] and in recent years. [8][9][10][11] Many properties of transition metals, such as the cohesive energy, the bulk modulus and the inverse atomic volume, which are often taken as manifestations of the strength of the interatomic bonding, show related behaviors for the 4d and 5d series. 12,13 This trend, in which the properties of chemically related substances vary in predictable manners, has been called ''homologous behavior''.…”

“…Fig.7Force constant parameters k Ecoh , k B and k( j), for the 4d and 5d transition metals derived from the cohesive energy (eqn (9)), from the bulk modulus (eqn(10)) and from the Debye temperature (eqn (8)), respectively, as functions of the Group Number (GN).…”