The diffusion of ions with multiple valence The oxidation of transition metal alloys

This paper analyses quantitatively some of the diffusion processes specific to oxides containing more than one transition-metal species. Such processes can be rate-determining in the oxidation of transition-metal alloys. In particular, we examine the processes which require two species, both of which can exist in more than one charge state. For these processes we assess the dominant terms (polarization, distortion and intra-atomic energies) in the key energies for formation, stability and motion. The results indicate some new classes of process, in which the charge state at the saddle point differs from that at the initial and final jump positions. This type of process indicates a need for a generalization of the theory of rate processes, and corresponds to a number of previous suggestions for semiconductor systems.