Shifted Morphotropic Phase Boundary in [111]-Oriented Nb-Doped Pb(Zr x Ti1–x )O3 Epitaxial Films: Insights into Piezoelectricity and Domain Variation

Morphotropic phase boundary (MPB) in Nb-doped Pb­(Zr,Ti)­O3 thin films grown epitaxially on Nb:SrTiO3 (111) surfaces was studied by investigating their local piezoelectric response and domain structure using piezoresponse force microscopy. A sharp peak of piezoelectric coefficients was observed at Zr/Ti = 40/60, supporting the fact that the substrate constraint shifted the MPB in [111]-epitaxial Pb­(Zr,Ti)­O3 thin films toward the PbTiO3 side of composition from Zr/Ti = 52/48 for bulk materials. The domains at MPB also show a distinguishing structure with shrinking size and remarkably larger vertical piezoresponse compared to the single-phase samples. This work provided a deeper understanding about the effect of substrate constraint on the phase structures and electrical properties of epitaxial ferroelectric films.