Theory of The Oxidation of Metals and Semiconductors: The Phenomenon of Isoparametric Generation of Nonstoichiometric Point Defects in Anodic Oxide Films

Abstract

A unified theory of the oxidation of materials is formulated, according to which the differences between these processes are related to the degree of deviation from equilibrium of the processes of the generation and recombination of point defects at the boundary of the oxide film, which are responsible for mass transfer. Anodic oxidation occurs under nonequilibrium conditions and is controlled by the rate of generation of two types of basic point defects. The generation of both defects is characterized by the identity of parameters, and occurs as a result of a jump of the same particle (oxygen ion or metal) at the boundary of the oxide film, and this explains the phenomenon of simultaneous mobility of anions and cations. The mechanisms of isoparametric generation of a pair of point defects are proposed: the initiating jump mechanism and the displacement mechanism. Their implementation in oxides with excess or deficiency of oxygen is shown. Criteria are proposed for determining the mechanism of generation of defects during the oxidation of various substances. The conditions of thermal oxidation are close to equilibrium, and point defects have time to recombine at the oxide boundary; therefore, defects with a higher recombination activation energy predominate.

Reactive-Vacancy Mechanism of Pore Growth in Oxide Films

“…Let us consider the transfer of point defects through pores formed in the oxide on the assumption that there is no interaction between defects. Similar to how it happens at the boundary with the metal according to V.Ovchinnikov, 3 oxygen on z E-mail: ovchinnikov@unitest.ru the pore surface facing the electrolyte leaves the oxide lattice under the action of a strong electric field and, moving towards the metal, passes into the pore volume (see Fig. 1).…”

“…As V. Ovchinnikov 3 teaches, in oxides with a deficiency of oxygen, the generation of interstitial metal ions and oxygen vacancies occurs at the oxide-metal interface by the displacement mechanism. At the boundary with the metal, new sites of the oxide lattice are formed as a result of the jump of an oxygen ion from the site of the oxide film into the metal.…”

“…3, interstitial oxygen ions and cation vacancies migrate from the outer boundary of the film towards the oxide-metal interface. 3 Effect of point defect transfer on pore movement in oxide.-After reaching the pore surface, the interstitial oxygen ion O i 2− passes into the pore cavity in the form of gaseous oxygen. This transition is expressed by the reaction:…”

“…The space charge of metal vacancies can be neglected due to their low concentration in the film. 3 The field strength of the space charge of defects was determined using the Poisson equation:…”

“…V. Ovchinnikov 3 teaches that nonstoichiometric point defects can form only at the phase boundary, in contrast to Frenkel defects, which are formed in the bulk of the oxide. But the pores in the films create internal phase boundaries.…”