Energy effects on alloying through a re-interpretation of the parameters of Miedema

Abstract

The parameters Phi and N of Miedema are quoted precise to the second decimal place and are considered very accurate after adjustment in their values to correctly predict the signs of the heats of formation of more than 500 metallic binary systems. In this paper, we argue that Phi is proportional to the electronegativity (Chi) of metallic elements and that N^(1/3) is the valence effective on a linear bond. We show that, with the above hypothesis, Chi can be derived in the absolute sense, following Gordy, as the electrostatic potential due to the effective charge of the nucleus of an atom in a metal, felt at the mid-point of a bond to the nearest atom. The exponent 1/3 has its origin in the high ligancy and resonance in metals. An excellent agreement with the hypothesis is observed for the hypoelectronic elements, while the buffer and hyperelectronic elements show interesting variations. It is argued that the unlike atom pair bond energies, which are correlated to the distribution of binary systems on the map constructed using the magnitudes of parameters del Phi and del N of Miedema, originate from the scatter in the distribution of elements in the electronegativity versus N^(1/3)/R graph. Since it is the scatter that is important, we see that the small corrections effected by Miedema et al. to the parameters Phi and N are significant in deciding the energies involved. An interpretation is provided for the energy effects involved in the alloying of metals.