Tuning electrical conductivity, charge transport, and ferroelectricity in epitaxial BaTiO3 films by Nb-doping

The electrical conductivity, charge transport behavior, and ferroelectricity of epitaxial BaNb x Ti1- x O3 films (BNTO, 0.0 ≤ x ≤ 0.5) prepared by pulsed laser deposition are investigated. It is found that Nb-doping can tune the conventional insulating BaTiO3 films from an insulating to highly conductive semiconducting or metallic state, resulting in a variation of the electrical conductivity of the BNTO films over 105. For x ≤ 0.25, the charge transport is dominated by the small polaron hopping mechanism, while the charge transport for x = 0.5 transits from the bipolaron to the small-polaron, and then the thermal phonon scattering mechanisms with increasing temperature. Interestingly, the piezo-force microscopy imaging reveals the presence of ferroelectricity in the properly Nb-doped conductive BNTO films (x ≤ 0.25) deposited in the presence of a small amount of oxygen (3 × 10−3 Pa). Our work provides additional technical roadmaps to manipulate the conductivity and charge transport behaviors in ferroelectric films, which will boost potential applications in future information storage, sensors, and photovoltaic devices.