Artificial phase separation in PZT superlattices: Structural foundations for investigating morphotropic phase boundary physics

Understanding how structural length scales influence the electromechanical response of morphotropic ferroelectrics remains an open challenge, in part because conventional solid-solution systems such as Pb(Zr,Ti)O3 (PZT) naturally exhibit chemical disorder. Artificially layered superlattices offer a route to impose controlled phase separation down to the unit cell level, yet achieving coherent growth of PbTiO3 (PTO) and PbZrO3 (PZO) layers has proven difficult due to their large lattice mismatch. In this work, we demonstrate the successful synthesis of coherently strained PTO-PZO superlattices with nanometer-scale periodicities by employing rare-earth scandate substrates, whose intermediate in-plane lattice constants minimize mismatch for both constituents. High-resolution x-ray diffraction (HR-XRD) reveals well-defined superlattice satellite peaks, and scanning transmission electron microscopy with energy-dispersive x-ray spectroscopy (STEM-EDS) mapping confirms sharp interfaces and controlled compositional layering. These results establish the key conditions required to engineer PZT-based superlattices with true atomic-scale precision and provide a robust platform for future investigations into the influence of controlled phase separation on morphotropic phase boundary (MPB) behavior. While the average composition of the superlattices is close to the PZT MPB, the present work is limited to their structural realization and characterization. Consequently, no conclusions regarding ferroelectric, dielectric, piezoelectric, or other MPB-related functional properties are drawn; such studies will be the subject of future work.