Electromechanical properties of sol-gel derived Ca-modified PbTiO₃ films

Piezoelectric coefficients and electric field-induced strains are investigated in Ca-modified PbTiO₃ (PCT) films deposited by sol-gel technique. The microstructural evolution and related electromechanical properties are studied as a function of Ca content and porosity of the films. The porosity is tailored by changing the heating rate during the final crystallization anneal. It is found that piezoelectric properties of porous films heated at slow rates are superior to those of dense films crystallized using higher heating rates. This is explained as a result of the constraining effect of the substrate, which apparently reduces the piezoelectric and strain responses in dense films. Electromechanical properties are also improved with Ca addition due to the decrease of tetragonality and ease of 90° domain rotation. Charge piezoelectric coefficients in porous films are close to those of PCT ceramics of the same composition. These results, combined with the low dielectric constant, make PCT films an attractive material for microelectromechanical applications.