Cluster and Short-Range Order Influence on the Electrical Resistivity of Binary Alloys

Abstract

The main aim of this work was to find some approach to the calculation of electrical transport properties for concentrated binary alloys from first principles in order to study the influence of short-range order on the electrical resistivity. The theoretical treatment relies on an one-electron picture, within the framework of density functional theory, using the multiple scattering theory to solve the electronic structure problem. For transport calculations the Kubo-Greenwood formula of linear response theory was used. The multiple scattering theory shows that the scattering path operators, that result from the decomposition of the Green function, are the most important quantities involved in the calculation of observables. It was shown how scattering path operators could be calculated by means of cluster methods in order to allow the take into account of information about the local arrangement of atoms in a cluster. The embedded cluster method (ECM), was already used in many calculations of electronic properties and was shown to give reliable results. Its applications to resistivity calculations was, however, only sporadic. The isolated cluster method (ICM) was for the first time applied to calculations of properties. The results showed that both ECM and ICM are well suited for modelling short-range order in alloys with high resistivity giving the right tendency of the change in the resistivity due to ordering processes. It was argued that the widespread procedure of including only up to d-states (l=2) in calculations of electronic properties is not appropriate when one aims to calculate electrical resistivities. For comparison of such calculations with experiment the inclusion of at least f-states (l=3) is absolutely necessary. It is, however, possible to study qualitatively resistivity changes even for l=2.