Crystallisation of Pb1−xCaxTiO3 ferroelectric thin films as a function of the Ca2+ content

Lead calcium titanate (Pb1−xCaxTiO3) thin films with x from 0 to 0.50 were prepared by chemical solution deposition. Crystallinity of the films was studied as a function of calcium content and processing temperature. These studies were carried out on films deposited onto oxidised (1 0 0) Si substrates by means of X-ray diffraction. The analysis seems to indicate that the grain size of the films decreases as Ca2+ content increases, which was confirmed from the scanning force microscopy images of the films. X-ray data reveal that kinetics of grain growth in films with Ca2+ contents over 40 at% is very slow. Increase of calcium also produces a decrease in tetragonality of the perovskite films. Besides, it was observed that reflections of the perovskite appear at higher temperature in the films with larger Ca2+ contents. Brillouin spectroscopy was used to follow the evolution of the elastic properties of the films with temperature. This study shows an elastic instability at temperatures between 475 °C and 500 °C that can be associated to complete film crystallisation. Dielectric and ferroelectric properties were measured on films deposited onto platinised silicon substrates and crystallised at 650 °C. The films with 50 at% of Ca2+ still have ferroelectric properties, showing diffuse ferro-paraelectric transitions and slim ferroelectric hysteresis loops.