Punktfehlstellen in Oxidmischphasen II. Beweglichkeit der Defektelektronen in (CoxMg1‐x) O und (CoxMg1‐x)2 SiO4

1974

Relations between tracer diffusion coefficients and interdiffusion coefficients for quasibinary oxide solid solutions are derived. It is demonstrated that under certain conditions Darken‐type equations are obtained. By inserting experimentally determined interdiffusion coefficients and tracer diffusion coefficients in the Darken relation for (Co,Mg)O and (Co,Ni)O at 1300°C in air it is shown that the Darken‐type equation cannot be employed for interdiffusion in these systems. This is attributed to deviations from local point defect equilibrium in the diffusion couple, which is contrary to a major assumption in the derivation. Experimentally determined interdiffusion coefficients and tracer diffusion coefficients for Co‐cations are reported for various compositions in (Co,Mg)O at 1300°C in air.

Interdiffusion in (A,B)O‐type Solid Solutions and the Validity of Darken′s Equation

Yurek

1974

Deviations from Local Thermodynamic Equilibrium During Interdiffusion of CoOMgO and CoONiO

Yurek

1975

The assumption of local thermodynamic equilibrium during interdiffusion between CoO and MgO and between CoO and NiO at a given oxygen potential of the ambient atmosphere is discussed. Although the oxygen anions are virtually immobile, macroscopic markers (pores, Pt) move toward the CoO‐rich end of the metal‐deficient semiconducting oxide during interdiffusion. It is shown independently that the markers move under the action of an oxygen potential gradient opposite to the vacancy flux. The existence of a gradient in the oxygen potential in the diffusion zone shows that local equilibrium is not established. It is found that the deviations from local equilibrium do not, within the range of experimental uncertainty, result in time‐dependent interdiffusion coefficients.

Point defects in oxide solid solutions (III) mobilities of cations and vacancies in (Co, Ni)O‐ and (Co, Mg)O‐solid solutions and the calculation of correlation factors

Dieckmann

1975

Correlation effects in the diffusion of cations of B 1‐type solid solutions (A,B)O are discussed on the basis of the different elementary jump frequencies of these cations. In the theoretical part, the correlation factors of the cations are expressed in terms of the tracer diffusion coefficients or the elementary jump frequencies of the cations and the composition of the solid solution. Furthermore, relations for the vacancy diffusion coefficient and the interdiffusion coefficient are given. In the experimental part, the tracer diffusion coefficient of Co in (Co, Mg)O is determined. In view of experimental results obtained for the analogous system (Co, Ni)O, the diffusion coefficients of magnesium ions and of vacancies are calculated. The latter can be compared with experimental data obtained by relaxation measurements. The fair agreement supports the assumptions made in the theory.