Measurement of reduction kinetics in Nb2O5-doped SrTiO3 by use of a new technique of liquid film migration

To investigate the reduction kinetics of Nb2O5-doped SrTiO3, which has previously been difficult because of its low diffusivity, we have developed a new technique for the measurement of chemical diffusivity using the phenomenon of liquid film migration. 0.2 mol%-Nb2O5-doped SrTiO3 powder compacts were sintered in air and then annealed at various temperatures and for various periods of time in 95N2/5H2. During the annealing the surface of individual grains was reduced and the thickness of the reduced layer varied with the annealing temperature and time. As a CuO melt was infiltrated into the annealed samples, liquid film migration occurred and eventually stopped when the reduced layer was swept. It was therefore possible to measure the thicknesses of the reduced layers under different annealing conditions. Based on the measured migration thicknesses, the chemical diffusion coefficient, Dchem, during reduction of 0.2 mol%-Nb2O5-doped SrTiO3 was determined to be Dchem=4.6×104exp[−(489±118kJ)/RT] (cm2 s−1). Comparing the diffusion coefficient and activation energy with previous data showed that the reduction was governed by the diffusion of Sr ions. The present investigation demonstrates a new technique for the study of oxidation/reduction kinetics in systems where the lattice parameter varies with oxygen partial pressure.