Thickness-Dependent Phase Transition and Piezoelectric Response in Textured Nb-Doped Ph(Zr0.5Ti0.48)O3 Thin Films

[100]-textured Nb-doped Pb(Zr0.52Ti0.48)O-3 (PNZT) films with different thicknesses from 80 to 600 mm were fabricated on Pt(111)/Ti/SiO2/Si(100) substrates by a sol-gel process. It was found that the local effective longitudinal piezoelectric coefficient, (133, initially increased with film thickness and reached a peak (-220 pm/V) for an intermediate thickness (similar to 350 nm). but then decreased with further increasing thickness. XRD and Raman analyses revealed that, even for an identical Zr/Ti ratio of 52/48, which is near the morphotropic phase boundary of bulk PZT, a pseudophase transition from a tetragonal structure to a rhombohedral structure was induced in [100]-textured ONZT films because of changes in stress with film thickness. This finding revealed a special approach to enhance the piezoelectric properties of PZT-based thin films by combining compositional optimization and the substrate constraint effect.