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

Abstract

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.

Crystalline Oxide Solid Solutions in Oxygen Potential Gradients

“…In accordance with this discussion the steady state demixing is the result of a cation vacancy flux from the high oxygen potential surface to the low oxygen potential surface and the higher jump frequency of Co-ions into a neighbouring vacancy as compared with the jump frequency of Mg-ions [6] instable during its motion towards the high oxygen potential side, since any disturbance in form of an indentation of the plane surface with a corresponding higher vacancy gradient increases the flux of vacancies towards this disturbance, thus enhancing the indentation growth. This self-accelerating process results in a jagged low oxygen potential surface with pores which, after some time, can be found throughout the crystal between the highand the low oxygen potential side.…”

“…Correlation effects are found if the elementary jump frequency /A of an A-cation into a neighbouring vacancy differs from PB-The effective jump frequencies that determine the cation mobility and diffusivity differ from f by a correlation factor which is concentration dependent [6]. It is in principle possible to obtain additional information on correlation effects in oxide solid solutions by a comparison of calculated demixing profiles (including correlation effects) with experimentally determined steady state concentration profiles.…”

Mechanistic Studies with Mass Spectroscopic Cyclic Voltammetry: Anodic Oxidation of Hydroxylamine on Pt

“…porous Teflon membrane as the hydrophobic barrier between the electrolyte on the one side and the vacuum of the mass spec on the other side [7), this being the inlet system. A porous catalyst layer (Pt in the present case) is attached to the membrane and serves as the working electrode.…”

Cr diffusion in orthopyroxene: Experimental determination, 53Mn–53Cr thermochronology, and planetary applications

“…A possible explanation of the observed negative effect of f(O 2 ) on D(Cr) may lie in the presence of a significant component of interstitial mechanism for the diffusive transport of Cr. The negative correlation between D and f(O 2 ) was first explained by Dieckmann and Schmalzried (1975) in terms of interstitial mechanism in their study on the effect of f(O 2 ) on diffusion of Fe in magnetite.…”

“…Thus, we assume that chromium diffused onto orthopyroxene as Cr 3+ ion. Following the analysis of Dieckmann and Schmalzried (1975), we can write for interstitial diffusion of Cr 3+…”