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

Abstract

Ba_1-xCaxTiO₃ 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-xCa_xTiO₃ 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 dielectric phase transition temperature of (Ba_1-xCa_x)TiO₃ 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>0.05at.%). The laser ablated Ca-doped BaTiO₃ thin films deposited 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 Ca²⁺ in the Ti4+ site. There was a cross over from the sharp to diffused phase transition for a higher composition of Ca (>9 at.%) in BaTiO₃ thin films. The diffuse transition behavior might be due to the larger number of the Ca²⁺ ions occupying the Ti⁴⁺ 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.