13 - Densification and Grain Growth in Ionic Compounds

Abstract

The transport of ions during the densification of ionic compounds occurs not only by a chemical potential gradient coming from a difference in capillary pressure but also by an electrical potential gradient derived from the difference in diffusivity between different ions. An electrostatic potential in the material affects the segregation of ions at the grain boundary, and further affects the grain boundary migration and grain growth. During the densification of ionic compounds, material transport occurs mostly by diffusion with the material maintaining its stoichiometry. The diffusion of each ion species occurs under a chemical potential gradient derived from a capillary pressure difference and an electrical potential gradient resulting from a difference in the mobility of the cation as well as the anion. The diffusion fluxes of cations and anions are interrelated, and occur in the same direction. Driving force for the diffusion of ions is thus the electrochemical potential gradient, the sum of the chemical potential gradient, and the electrical potential gradient.