ELECTRONIC AND LATTICE EXCITATIONS IN BATIO3-LA

We report lattice and electronical properties of BaTiO3:La powders and ceramics with 0 < x(La) < 20 at.%. Dielectric measurements and x-ray scattering evidence a continuous decrease of the ferroelectric transit ion temperature when the La content is increased. For x(La) = 20 at.%, no dielectric maximum is found for temperatures higher than 20 K. At the same time, an impurity mode at 840 cm(-1) increases linearly with x(La),. We have modelled these data using a linear chain model with on e polarizable ion. The electric excitations were probed using DC condu ctivity, EPR spectroscopy and optical absorption. This last technique was applied to BaTiO3:La single crystals, which were grown for the fir st time in our laboratory. Our main result is that the conductivity ma ximum at x(La) approximate to 0.5 at.% is related to an impurity level lying 2.1 eV below the conduction band.