High‐Temperature Defect Structure of Acceptor‐Doped Strontium Titanate

Abstract

The defect structure of acceptor‐doped (Fe, Al, Cr) polycrystalline strontium titanate was investigated by measuring the equilibrium electrical conductivity as a function of oxygen activity (10−21≤ao2≤1) and temperature (85°C≤T≤ 1050°C). The electrical conductivity was n type with ∼−1/4 dependence on a02 for a02<10−10. For a02>10−8, the observed data for Fe‐ or Al‐doped samples were proportional to ∼1/4.5 power of a02. In this region for Cr‐doped samples, the value of m in.σp αa02+1/m varies from ∼4.80 to ∼9.00 as the concentration of Cr is increased from 460 to 10 000 ppm. The onset of p ‐type conductivity depends on the amount. of acceptor impurity added to the sample. The absolute values of the conductivity in the acceptor‐doped samples were lower in the n‐type region than those for undoped SrTiO3. The conductivity minima shift toward lower oxygen activity with increasing acceptor concentration. For the entire oxygen activity rangae used in this study, the defect structure of SrTiO3 is dominated by the added acceptor impurities.