Conductivity, charge transport, and ferroelectricity of La-doped BaTiO3 epitaxial thin films

La-doped BaTiO3 thin films (BLTO) were deposited by pulsed laser deposition, and a comprehensive investigation on their conductivity, charge transport, and ferroelectricity was carried out. Resistivity-temperature (T) measurements demonstrate that the conductivity of Ba1-xLaxTiO3 ( x = 0.05, 0.1, 0.2, 0.3, and 0.4) films can be largely regulated in a wide range. The BLTO film exhibits typical semiconductor conduction behavior for x <= 0.3, whereas a typical metallic conduction behavior was observed for x = 0.4 at T > 240 K. The La doping concentration x also plays an important role on the charge transport mechanisms. For x <= 0.3, the charge transport follows small-polaron hopping at low temperature (T < 300 K) and thermal excitation at high temperature (T >= 300 K). While the charge transport for x = 0.4 changes from small-polaron hopping to thermal phonon scattering with the increase of temperature. Piezo-force microscopy measurements reveal that BLTO films exhibit ferroelectricity for La doping concentration x up to 0.4. These results demonstrated that La doping plays an important role in regulating the conductivity and charge transport in BLTO films. More importantly, we revealed experimentally that macro metallic conduction and ferroelectricity can coexist in the La-doped BaTiO3 epitaxial thin films.