The chemical diffusion coefficient of ceramics doped with Y and Mn (donor-doped and

acceptor co-doped) were determined by means of conductivity relaxation experiments. The equilibrium values of the electronic conductivities of n-conducting BaTiO3 were analyzed by applying a defect chemical model which involved electrons and cation vacancies as the predominant defect species under oxidizing conditions (fairly high O partial pressures). The relaxation curves of the electronic conductivity yielded the chemical diffusion coefficient of the bulk upon employing a spherical grain model in which the appropriate diffusion length was the radius of the grain (average grain size). The conductivity relaxation experiments were performed at 1100 to 1250C under O partial pressures of 0.01 to 1bar. The kinetics of the O exchange process could be interpreted in terms of an extremely fast diffusion of O via O vacancies along the grain boundaries, and slow diffusion of Ti (cation)-vacancies from the grain boundaries into the grains. The Ti-vacancy diffusion coefficients were extracted from the chemical diffusion coefficients as a function of temperature. Typical values for the Ti-vacancy diffusivity were around 10−15cm2/s, with an activation energy of 3.9eV.

Electronic Conductivity and Chemical Diffusion in n-Conducting Barium Titanate Ceramics at High Temperatures. W.Preis, W.Sitte: Solid State Ionics, 2006, 177[35-36], 3093-8

Table 22

Diffusion of O in Ba103.75Ti100.6Mn2Ox with Various Additions