An extension of the Engel-Brewer metallic correlation to transition metal silicides

Transition metal silicides are of considerable technological importance. In integrated circuits, they are used as gate electrodes, Schottky barriers and as ohmic contacts. In spite of the large amount of research being done on these materials, there is very little understanding of the physical and chemical factors that determine the material properties. The reason for the lack of progress is best demonstrated by considering the crystal structure. The crystal structures of all transition metal silicides fall into just four crystal systems (cubic, hexagonal, orthorhombic and tetragonal). However, any analysis is made extremely difficult by the complexity of the different atom coordinations. In addition, the ground state electronic configurations of the gaseous atoms do not necessarily represent the electronic states of the atoms in the solid components. Thus, predicting electrical properties based on the ground state configuration leads to erroneous results. In this paper, we extend the well-known Engel-Brewer correlation for transition metals to transition metal silicides. Properties, such as resistivity, crystal structure, thermodynamic stability, bulk density, heat of formation and thermal expansion coefficient will be correlated to the promoted electronic state. We will show this correlation to be a useful predictive mode.