Reaction front occurrence on imperfection profiles during oxygen chemical diffusion in oxides. II. Kinetic analysis

TL;DR

This theoretical study analyzes how oxygen diffusion affects metal dopant states and conduction types in oxides, revealing conditions for reaction front formation and diffusivity behavior across different oxygen pressures.

Contribution

It provides a detailed kinetic analysis of oxygen vacancy diffusion and its impact on electronic properties, highlighting conditions for reaction front occurrence in oxides.

Findings

Oxygen vacancy diffusion shows constant diffusivity between critical pressures.

Reaction fronts occur under specific oxygen pressure conditions.

Diffusivity sharply increases outside the critical pressure range.

Abstract

We present a theoretical study of the impact of oxygen diffusion in oxide crystals on metal dopants ionic state and the conduction type under dynamic changes. The slow changes under thermal equilibrium are provided in a companion, Part I paper. Oxygen vacancy formation acting as a shallow, double-electronic donor, is assumed to result from the crystal exposure to a low ambient oxygen pressure. Critical transitions from n- to a p-type at an oxygen partial pressure Pi, and in ionization state of the metal dopant at an oxygen partial pressure PM, are usually not simultaneous, and depend on the different reaction constants. Invoking ambipolar diffusion for all participating species, it is shown that oxygen vacancy diffusion exhibits well defined characteristics in specific regions of the vacancy concentration related to the said critical pressures. Particularly, the oxygen chemical diffusivity is practically constant between Pi and PM, and increases sharply for pressures P << Pi,PM and P >> P,PM. Prominent reaction fronts occur under specific conditions in the two latter regions.