Calcium modified lead titanate thin films for electromechanical applications

Abstract
Electromechanical properties of Pb_l-xCa_xTiO₃ (PCT) thin films prepared by sol-gel technique are investigated as a function of Ca content. Crystallization of a perovskite phase is observed for the films subjected to the rapid thermal anneal at 650 °C. A small amount of pyrochlore phase is found for low Ca concentration (x=0.08). Tetragonality of the films is gradually decreased with Ca addition in qualitative agreement with bulk ceramics data. Piezoelectric coefficient, d₃₃, measured by optical interferometry initially increases with Ca content reaching a maximum at x=0.24. At this concentration, d₃₃ of 70 pm/V is observed which matches well the value for bulk PCT ceramics. The strain developed at 400 kV/cm is progressively decreased with Ca reflecting a decrease in tetragonality of the films. The observed difference in piezoelectric coefficients of PCT films and bulk ceramics is qualitatively explained by the clamping effect of the substrate and by depoling of the films due to the influence of depolarizing field.