Charge compensation mechanisms in La-doped BaTiO3

The mechanism of doping BaTiO3 with La has been investigated by a combinati on of X-ray diffraction, electron probe microanalysis, scanning and transmi ssion electron microscopy and impedance measurements. Phase diagram results confirm that the principal doping mechanism involves ionic compensation th rough the creation of titanium vacancies. All samples heated in oxygen at 1 350-1400 degreesC are electrical insulators, consistent with an ionic compe nsation mechanism. Samples heated in air or atmospheres of low oxygen parti al pressure, at similar temperatures, lose a small amount of oxygen and thi s gives rise to a second, electronic compensation mechanism in addition to the main, ionic compensation mechanism; as a result, samples are dark-colou red and semiconducting. The change from insulating to semiconducting behavi our is reversible, by changing the atmosphere on heating at 1350-1400 degre esC. We find no evidence for any changes in cationic composition of the BaT iO3 solid solutions arising from changes in oxygen content.