Effect of oxygen content on the dielectric and ferroelectric properties of laser-deposited BaTiO3 thin films

BaTiO3 thin films were epitaxially grown on SrTiO3 (001) and LaNiO3/SrTiO3 substrates by pulsed laser deposition under different oxygen pressures. The oxygen content in the BaTiO3 films was determined using modified Rutherford backscattering. The structural characteristics of the films were analysed by x-ray diffraction theta /2 theta scan, phi scan, and symmetric and asymmetric omega scans. The dielectric and ferroelectric properties of the films were measured by an impedance analyser and by a Sawyer-Tower circuit, respectively. It was found that the atomic ratio of O/Ba and Ti/Ba in the BaTiO3 films increases with oxygen pressure. The films fabricated in the intermediate oxygen pressure range of 2 to 10 Pa show the c-axis oriented tetragonal structure with a stoichiometry close to the ideal value. These films exhibit a relatively large dielectric constant, small dielectric loss and good ferroelectricity with a symmetric hysteresis loop. For growth at low oxygen pressure i.e. 0.1 Pa, the film with tetragonal c-axis orientation shows significant degradation in its dielectric properties. For a higher deposition oxygen pressure of 20 Pa, the film has tetragonal a-axis orientation and shows no ferroelectricity but has the largest dielectric constant.