Epitaxial strain is a powerful tool to manipulate the properties of ferroelectric materials. But despite extensive work in this regard, few studies have explored the effect of epitaxial strain on PbZr0.52Ti0.48O3. Here we explore how epitaxial strain impacts the structure and properties of 75 nm thick films of the morphotropic phase boundary composition. Single-phase, fully epitaxial films are found to possess "relaxed" or nearly "relaxed" structures despite growth on a range of substrates. Subsequent studies of the dielectric and ferroelectric properties reveal films with low leakage currents facilitating the measurement of low-loss hysteresis loops down to measurement frequencies of 30 mHz and dielectric response at background dc bias fields as large as 850 kV/cm. Despite a seeming insensitivity of the crystal structure to the epitaxial strain, the polarization and switching characteristics are found to vary with substrate. The elastic constraint from the substrate produces residual strains that dramatically alter the electric-field response including quenching domain wall contributions to the dielectric permittivity and suppressing field-induced structural reorientation. These results demonstrate that substrate mediated epitaxial strain of PbZr0.52Ti0.48O3 is more complex than in conventional ferroelectrics with discretely defined phases, yet can have a marked effect on the material and its responses. The role of epitaxial strain in affecting the properties of PbZr0.52Ti0.48O3 films is explored. Complex domain structures and property evolution are found despite films possessing nearly "relaxed" structures indicating that the elastic constraint from the substrate produces residual strains that dramatically alter the electric-field response including quenching domain wall contributions to the dielectric permittivity and suppressing field-induced structural reorientation.

Domains and domain walls are critical in determining the response of ferroelectrics, and the ability to controllably create, annihilate, or move domains is essential to enable a range of next-generation devices. Whereas electric-field control has been demonstrated for ferroelectric 180° domain walls, similar control of ferroelastic domains has not been achieved. Here, using controlled composition and strain gradients, we demonstrate deterministic control of ferroelastic domains that are rendered highly mobile in a controlled and reversible manner. Through a combination of thin-film growth, transmission-electron-microscopy-based nanobeam diffraction and nanoscale band-excitation switching spectroscopy, we show that strain gradients in compositionally graded PbZr1-xTixO3 heterostructures stabilize needle-like ferroelastic domains that terminate inside the film. These needle-like domains are highly labile in the out-of-plane direction under applied electric fields, producing a locally enhanced piezoresponse. This work demonstrates the efficacy of novel modes of epitaxy in providing new modalities of domain engineering and potential for as-yet-unrealized nanoscale functional devices.