Characterization of lanthanum-doped barium titanate ceramics using impedance spectroscopy

The electrical properties of two single-phase, lanthanum-doped BaTiO3 compositions, x = 0.03 and x = 0.20, in Ba1-xLaxTi1-x/4O3 were investigated by impedance spectroscopy after heat treatment in oxygen, argon, and air at 1350 degreesC. Samples heated in oxygen were electrically insulating, whereas those heated in argon lost oxygen and were semiconducting at room temperature, irrespective of x, Samples heated in air showed intermediate electrical properties and also were electrically inhomogeneous; the two compositions showed different electrical behaviors, and a model for each, based on oxygen nonstoichiometry within the ceramics, is proposed, Oxygen deficiency in samples sintered in air was avoided by heating at 1200 degreesC, instead of 1350 degreesC. Alternatively, oxygen lost from ceramics heated in air at 1350 degreesC was regained by postannealing in oxygen at 1350 degreesC.