Hybrid polar state in epitaxial (111) PbSc0.5Nb0.5O3 relaxor ferroelectric films
In relaxor ferroelectrics, the interplay between the short-range-order dipolar state and long-range-order ferroelectric state leads to outstanding response functions, which enable valuable capacitor, electromechanical, pyroelectric, and electrocaloric applications. Advanced applications are envisaged with epitaxial relaxor ferroelectric films, whose fundamentals are still poorly explored. In particular, frustration of ferroelectricity, contrasting the bulk behavior, has been found and ascribed to nonpolar crystal orientation in (001) epitaxial films of archetypical lead-based relaxors. Here, a peculiar hybrid polar state, where coexisting long-range and short-range orders persist to very low temperatures, is demonstrated in epitaxial polar-oriented (111) PbSc0.5Nb0.5O3 films. The hybrid state is evidenced by relaxorlike frustrations of ferroelectric transition and the Curie-Weiss behavior, validity of the Vogel-Fulcher relationship, a non-Rayleigh dynamic nonlinearity, and a ferroelectriclike low-temperature polarization. Local fluctuations of lattice strain arising from the relaxation of large epitaxial misfit are suggested to be responsible for the hybrid polar state. Introducing strain fluctuations by doping or nanostructuring is anticipated to boost the dynamic dielectric and piezoelectric performance of many perovskite oxide ferroelectrics.