The optical absorption of reduced and doped SrTi03 has been measured between 0.39 and 7 p,m. Transport measurements were also carried out between room temperature and 10 K for various samples with different treatment. Both optical and transport properties were found to depend greatly on the methods of preparations of the samples. We found up to five absorption peaks in the visible and infrared regions, lying at 0.43, 0.52, 0.70, 1.2, and -4, 8 p, m. In all samples, the so called free-carrier absorption tail starts falling off at about 2.5 p,m and has a maximum between 4.5 and 5 p, m. The position of this peak cannot be explained by the free-carrier absorption theory of LO-mode scattering.The new absorption mechanisms are introduced in order to explain the results in this wavelength region. Of the five absorption peaks, the first, second, and fourth peaks are due to impurity or defect levels, whereas the third and fifth peaks are interpreted as being due either to interconduction-band or vacancy-level to conduction-band transitions. The conduction and scattering mechanisms are discussed.

We have made measurements of the Hall effect and resistivity as well as of thermoelectric power in the temperature range 300–450 K. The results of these measurements are interpreted in terms of a small polaron model of conduction. Additionally, our resistivity and thermoelectric power measurements were extended to 1200 K in an attempt to elucidate the nature of the transition in conductivity occurring in the range 1071–1103 K. For the c direction, this transition appears to be from a semiconducting to a metallic state and a possible explanation for this is given in terms of a lattice distortion model.

A description is given of the heat treatment, under controlled conditions, of crystals of strontium titanate, both pure and niobium-doped, and of the effect of this treatment on the defect states in this material. Our analysis is based on evaluation of the results of electrical conductivity and Hall effect measurements, and those of optical absorption.

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