Oxidation Kinetics of Single-Crystal SrTiO3

Abstract

The oxidation kinetics were determined for single-crystal SrTiO3 by measuring the time and temperature dependence of the weight gain of reduced crystals. The oxidation can be described as a diffusion-controlled process. The calculated diffusion coefficients between 850° and 1460°C are represented by D= 0.33 exp (-22.5 ± 5.0 kcal/RT) cm2/sec. Directly measured oxygen ion diffusion coefficients in the same temperature interval reported earlier are interpreted as being extrinsic and can be represented by D= 5.2 × 10−6 exp (-26.1 ± 5.0 kcal/RT) cm2/sec, where the activation energy is for mobility only. Assuming that the calculated diffusion coefficients are for vacancy diffusion and the two activation energies are equivalent within experimental error, a vacancy concentration (fraction of vacant lattice sites), [O□], fixed by impurities in the fully oxidized crystal is calculated to be 1.6 × 10−5 by virtue of the relation between the oxygen self-diffusion coefficient, D02-, and the oxygen vacancy diffusion coefficient, Do□; Do2-= [O□]Do□ where the oxygen ion concentration [O2-] is taken as unity.