P-type partial conductivity of donor(La)-doped BaTiO3

P-type partial conductivity has been determined on donor (La-Ba(.))-doped BaTiO3 in full thermodynamic equilibrium state at a fixed temperature of 1200degreesC: For the nominal compositions of Ba0.99La0.01Ti0.9975O3, Ba0.99La0.01TiO3 and Ba0.985La0.01TiO3, the p-type conductivity is found to vary with oxygen activity as sigma(p) = (sigma(m)/2)(a(O2)/a(O2)*)(+1/4) with sigma(m) approximate to 0.01 S cm(-1) and a(O2)* approximate to 32, 120, 310, respectively, in the a(O2) region where conventionally the electronic conductivity varies as sigma proportional to a(O2)(1/4) and hence, the doped donors are believed to be compensated by cation vacancies (say, [La-Ba(.)] approximate to 4[V-Ti()]). This experimental fact supports that in the vicinity of the stoichiometric composition of the system which falls approximately at a(O2) = a(O2)*, while cation vacancy concentration is fixed by the donor concentration, oxygen vacancy concentration in the minority is also essentially fixed, thus, keeping the activity of TiO2 (or BaO) fixed. It is consequently suggested that donor-doped BaTiO3 contains a second phase even in its stoichiometric regime.