The effect of space-charge formation on the grain-boundary energy of an ionic solid

Abstract

Taking the model system of an oxide containing acceptor dopant cations and charge-compensating oxygen vacancies, we calculate at the continuum level the change in the excess grain-boundary energy of an ionic solid upon space-charge formation. Two different cases are considered for the space-charge layers: (i) only vacancies attain electrochemical equilibrium and (ii) both dopants and vacancies attain electrochemical equilibrium. The changes calculated for a specific set of grain boundaries indicate that, depending on dopant concentration, space-charge formation can decrease the excess free energy by up to 15% in the first case and by up to 45% in the second case. The possibility of the excess grain-boundary energy going to zero and the possible effects of an external electric field on the excess grain-boundary energy are also discussed. This article is part of a discussion meeting issue ‘Energy materials for a low carbon future’.

Hydration Entropy and Enthalpy of a Perovskite Oxide from Oxygen Tracer Diffusion Experiments

“…In comparison with values reported for dry exchanges, these data are slightly lower at T > 823 K and substantially lower below this temperature. Space-charge potentials at extended defects in ionic solids are generated by the redistribution of charged, mobile point defects between a bulk phase and the extended defect. − In the present case, there are two charged, mobile defects that can redistribute ( and ); furthermore, the bulk concentrations of these defects vary considerably over the temperature range of interest [Figure (a)], from at the highest temperatures examined to at the lowest. The interplay of these factors may thus give rise to rich behavior.…”

Electric-field-assisted processing of ceramics: Nonthermal effects and related mechanisms

“…Differences in the Gibbs formation energies of defects between bulk and interface ( G seg ) drive the formation of space-charge zones. In acceptor-doped CeO 2 and SrTiO 3 , G seg for oxygen vacancies drives the formation of space-charge zones in which oxygen vacancies are depleted, [17][18][19][20] acceptor cations are accumulated, and cation vacancies are accumulated. Cation mobility along ( 7)…”

“…grain boundaries can thus be strongly accelerated within the space-charge zones because c def is much higher, 21 and experimental data for cation diffusion in these materials are consistent with this picture. Applying a field to modify G seg,v , and thus the effective c def , has been argued 18 to require E ∼ 10 10…”

Technological Challenges and Advancement in Proton Conductors: A Review

“…Numerous microstructural studies in acceptor-doped BaCeO 3 reports dopant segregation at the grain boundary core and pacifies the space charge potential to contribute toward unimpeded charge transport. This implies the magnitude of space charge potential follows a linear dependency with acceptor doping concentration. − Degree of dopant segregation differs with varying microstructural properties. Low dopant segregation in the case of low grain-sized PCs leads to proportionally large space charge potential.…”