A modest dc electric field markedly reduced the tensile flow stress at high temperatures in three polycrystalline oxides, i.e. MgO, Al2O3 and yttria-stabilized tetragonal ZrO2 (Y-TZP). The reduction in flow stress ΔσE in Y-TZP consisted of three components: (i) ΔσT due to Joule heating, (ii) δσE a rapid, reversible component obtained in on-off and electric-field step-tests and (iii) ΔσE the cumulative effect of the field on microstructure. Only ΔσT and δσE occurred in MgO and Al2O3. It was concluded that δσE results from a reduction in the electrochemical potential for the formation of vacancies corresponding to the diffusion of the rate-controlling ion in the space-charge at the grain boundary. The calculated magnitude of the space-charge zone width and its temperature and solute composition dependence were in accord with theory and experiment; ΔσE was attributed mainly to the retardation of grain growth by the field. The retardation could be due to one or more of several effects of the field upon the space-charge zone: an increase in the segregated solute ions, a decrease in grain boundary energy and/or a decrease in solute ion mobility.

Influence of an Applied DC Electric Field on the Plastic Deformation Kinetics of Oxide Ceramics. H.Conrad, D.Yang: Philosophical Magazine, 2010, 90[9], 1141-57