Charge transfers in structurally disordered alloys

Abstract

In this paper we study binary alloys with structural disorder, as in the liquid and amorphous states. These are studied by a semi-empirical iterative tight-binding procedure which is basically an extension of the extended Hiickel method. Information about the eigenfunctions is contained in the charge-bond order matrix whose diagonal elements are formally associated to point charges on the atoms. Recent calculations [1, 2] have shown that even in disordered systems of identical atoms the atoms acquire different charges due to the differences in the fields around them. Thus a charge distribution n(Q) can be defined, that gives the number of atoms with charges between Q and Q + dQ. In binary ordered alloys, there is usually a charge transfer from one type of atom to the other. If the alloys are disordered, with either compositional or structural disorder, then there appears a different charge distribution for each type of atom. Our results show that the effect of having two different atomic sizes in a random system leads to an electronic charge transfer towards the larger atoms, defined as the average of the corresponding distribution. The differences in ionization potentials obviously produce charge transfers to the atoms with higher ionization potentials. Thus depending on the particular alloy, these two effects can produce charge transfers in the same or in opposite directions.