Electronic transport properties of Sr1−xLaxTiO3 ceramics

Abstract

The electrical conductivity of Sr1−xLaxTiO3 ceramics (x≤0.4) and single crystals (x≤0.1) was investigated in the temperature range between 19 and 1673 K. The mobility was calculated from the carrier concentration, n, which was determined by Hall measurements as well as by a chemical Ti3+ titration. The mobility of the single crystals agrees well with a model originally developed for undoped strontium titanate. At low T and high n scattering by ionized donor centers predominates. Above room-temperature phonon scattering becomes predominant. Sr1−xLaxTiO3 ceramics follow the same model, but only if they had been previously reduced in water-free and oxygen-free hydrogen atmospheres. The behavior during the reducing and cooling process can be explained by a defect chemical model, using a set of constants developed in a former work. However, reduced in water saturated hydrogen the conductivity at low T decreases by decades compared to single-crystal data and cannot be explained anymore by the above-mentioned models. In conjunction with impedance spectroscopy experiments it was found, that in this case the electrical behavior of the ceramics is completely governed by grain-boundary phenomena. These high-ohmic grain boundaries may be depletion layers, which are formed or annihilated depending on the conditions of the preceding high-temperature process.