Charge transfer on the metallic atom-pair bond and the bond energy

Abstract

Following our recent report demonstrating the significance of the nearest-neighbor unlike atom-pair bond in metallic alloys, an equation for the energy of such a bond is presented in this study. The success of empirically derived Miedema's equation in predicting the signs of the heats of formation of metallic alloys is explained. The negative contribution to the energy stems from the ionicity in the bond. The charge transfer on the bond, suggested by Pauling to establish electroneutrality, contributes the positive term which is quantified in this study. The value of Miedema's empirically derived constant (Q/P) 1/2 and the origin of the R/P term follow from the present model. It is shown that the energy of the atom-pair bond, calculated using the model, in the compounds of MgCu 2 structure type are directly correlated to the experimental heats of formation of the compounds, and this fact enables the prediction of the heats of formation values for new compounds of the same structure type.

Atom pair bond approach: an efficient method for determining the lattice parameters of NiAs-type compounds and comparative analysis with computational databases

“…With c as electronegativity, obtained by normalizing Miedema's electronegativity F to Pauling's scale, and N as the metallic valence of elements [25] and identifying N 1 3 as electron density of an element on a bond, (called bond valence), an expression for the A-B bond energy was derived as…”

“…Here, k, which has the dimensions of energy, is equal to zero, for compounds without p elements; and k takes values up to a maximum of 0.5 eV, depending on the valence of the p element in the compound [25].…”

“…The list of 42 compounds that crystallize in NiAs type structure, collected from Pearson's compilation [19] , along with the electronegativity (χ) and bond valence of the electrons (N 1 3 ), derived [25] using the Miedema's parameters [23], are given in appendix (table A1). During the formation of a binary compound, charge transfer takes place between the atoms A and B, resulting in a change in their size from their elemental radii values [26], and this is driven by the difference in electronegativity of the atoms.…”

Correlation of the properties of quasi-ternary Ni-based superalloys computed from DFT to elemental properties enabling predictions on the behavior of metallic alloying elements

“…Miedema's electron density [28] represents values at the Wigner-Seitz cell boundary N ws rather than the outer number of electrons beyond the inert gas configuration. It has been shown that N ws represents the valence electron concentration per atom (N) of a metal elsewhere [29]. Further, it was demonstrated that the lattice parameters of the cubic L1 2 type compounds can be accurately predicted from just a knowledge of the elemental radii [2].…”

Nature of the bond in intermetallic compounds

“…It was earlier reported that using Miedema's parameters [1,2], concomitant and mutually exclusive crystal structure types in metallic binary systems can be predicted with excellent accuracy [3][4][5][6][7][8]. It was shown that the metallic bond in intermetallic compounds is local in nature [6].…”