Normal ferroelectric to relaxor behavior in laser ablated Ca-doped barium titanate thin films

Abstract

Ba 1−x Ca x TiO 3 thin films (x=0.05 to 0.17) were deposited on Pt-coated Si substrates using a pulsed excimer laser ablation technique. X-ray diffraction and scanning electron microscope studies of the Ba 1−x Ca x TiO 3 targets exhibit a polycrystalline nature and thin films also show the same but with a significant orientation along the (111) direction. Secondary ion mass spectrometer analysis reveals the presence of a sharper interface existing at the thin film substrate. The dielectricphase transition temperature of ( Ba 1−x Ca x ) TiO 3 targets were sharp and the transition temperature was found to decrease from 140 °C to 110 °C with an increase in the values of x (x>0.05 at. %). The laser ablated Ca-doped BaTiO 3 thin filmsdeposited at 100 mTorr exhibited a higher dielectric constant, lower dielectric loss, and an anomalous decrease in phase transition was observed. The anomalous phase transition decrease was ascribed to the occupancy of the Ca 2+ in the Ti 4+ site. There was a cross over from the sharp to diffused phase transition for a higher composition of Ca (>9 at. %) in BaTiO 3 thin films. The diffuse transition behavior might be due to the larger number of the Ca 2+ ions occupying the Ti 4+ site, eventually introducing larger compositional and structural disorder and this occupancy leads to the generation of oxygen vacancies. The activation energy obtained from impedance spectroscopy was 1.05 eV, and was attributed to the oxygen vacancy motion.