Reactive-Vacancy Mechanism of Pore Growth in Oxide Films

Abstract

It is known that deviation in the stoichiometry of the composition of chemical compounds is associated with nonstoichiometric point defects, namely vacancies and interstitial ions. Until recently, only the behavior of point defects in the bulk of a solid was considered, while the question of the appearance of point defects in chemical compounds, and where and how they appear, remained uninvestigated. Previously, we showed that nonstoichiometric point defects arise exclusively on the surface of a solid, and the mechanisms of their occurrence were given. However, phase boundaries can also appear inside a solid, and this is due to the presence of pores inside them. Here we propose that a reactive-vacancy mechanism for pore formation and growth in chemical compounds is based on a quasi-chemical reaction that occurs on the pore surface between nonstoichiometric point defects; vacancies in one sublattice and interstitial ions in the other. This reaction leads to the formation of vacancies in the second sublattice and, together with vacancies from the first sublattice, to the growth of pores.