Formation of point defects in strontium titanate

Abstract

The electrical conductivity and thermoelectric power of single crystal strontium titanate were determined as a function of the P H 2O P H 2 ratio over crystals at various temperatures. Electrical conductivity measurements were made in the temperature range from 900 to 1300°C; thermoelectric data were taken from 600 to 1300°C. A range of P H 2O P H 2 ratios from 2 × 10 −4 to 3 × 10 −2 was investigated. Typical values of the electrical conductivity at a temperature of 1000°C and P H 2O P H 2 ratios of 1× 10 −3 and 1 × 10 −2 were 1⋯2 Ω −1cm −1 and 0.53Ω −1cm −1, respectively; under the same conditions the thermoelectric power was found to be −0.600 mV/°K and −0.662 mV/°K. The thermoelectric measurements showed the crystals to be n-type. An oxygen vacancy defect model was found applicable to non-stoichiometric strontium titanate at elevated temperatures. In damp hydrogen the enthalpy of formation of an oxygen vacancy and two electrons in the conduction band was 86,500 ± 3000 cal mole .