Electrical Properties of Yttrium-Doped Strontium Titanate under Reducing Conditions

The electrical conductivity of containing rare earth dopants (Y, La, Pr, Sm, Nd, Gd, or Yb) was measured at 600-900°C in reducing atmospheres. An unusually high conductivity was observed for the yttrium-doped samples compared to those with rare earth dopants, particularly at the composition of the solubility limit where the conductivity at 800°C was 64 S/cm. The conductivity was confirmed to be n-type by thermopower measurements. The oxygen deficiency was determined to be 1% by thermogravimetric analysis. Increasing the strontium vacancy concentration to effected a further improvement in conductivity to 82 S/cm. This material has high structural stability over a broad range of temperature (up to 1400°C) and oxygen partial pressure A simple defect model was developed to explain the change of electrical conductivity as a function of yttrium content and oxygen deficiency.