Thickness and thermal processing contribution on piezoelectric characteristics of Pb(Zr-Ti)O₃ thick films deposited on curved IN738 using sol–gel technique

Lead zirconate-titanate (PZT) thick films of perovskite structure Pb(ZrxTi1-x)O3 were fabricated on the curved surface of IN738 nickel-based supper alloy substrate up to 15 µm thickness using sol–gel deposition technique without polyvinylpyrrolidone. The films were heated at 200℃ with 10 wt% excess PbO, pyrolyzed at 400℃, and subsequently annealed at 650℃, 700℃, and 800℃. Au and Pt thin films were deposited as bottom and top electrodes, respectively. PZT films of different thicknesses and thermal treatment conditions were characterized to investigate the effect of process on crystalline phase development, orientation, and microstructure morphology. Thereby, formation of fairly smooth, semi-dense, and crack-free random orientated thick films as well as an increase in the average grain size and stress relaxation was observed as the film thickness increased. Having optimized the coating process, intrinsic and extrinsic dielectric, ferroelectric and piezoelectric properties were measured as a function of the film thickness, orientation, grain size, and domain wall motions to evaluate the remnant polarization (P_r = 7.6–17.5 µC/cm²), coercive field (E_c = 2.5–4 kV/cm), permittivity (ɛ_r = 276–326), dielectric loss (tanδ(%) = 2.7–3), and piezoelectric charge coefficient (d₃₃ = 71–145 pm/V) of the PZT thick films prepared potentially to be used as high bandwidth 1–5 MHz structural health monitoring transducers.