Analysis of the film thickness dependence of the ferroelectric properties of epitaxial PMN–PT thin films on a thin PZT interfacial layer

Perovskite phase-pure, (001)-oriented, epitaxial [Pb(Mg1/3Nb2/3)O3]0.67–(PbTiO3)0.33 (PMN–PT) thin films with six different thicknesses in the range 100–1000 nm were deposited on single-crystal, (001)-oriented SrTiO3 substrates on a 25 nm Pb(Zr0.5Ti0.5)O3 interfacial layer. The measured ferroelectric, dielectric, and piezoelectric property values of parallel-plate capacitor structures increase with PMN–PT layer thickness. This is explained by increasing local polarization further away from the substrate, which is deduced from the properties of the thickness series. The polarization change is explained by strain relaxation with increasing thickness and also indicates a symmetry change from rhombohedral to tetragonal symmetry above a thickness of 800 nm. This correlates with an earlier found abrupt change of Young's modulus and hardness.