Hybrid polar state in epitaxial (111) PbSc0.5Nb0.5O3 relaxor ferroelectric films

Abstract

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) PbSc 0.5 Nb 0.5 O 3 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.

Polar state in polycrystalline BaSn0.3Ti0.7O3 thin film determined from ac- & dc-field studies

“…Adapting the standard nomenclature used for relaxors, domain like response & field induced transitions are seen in both the ergodic and non-ergodic phases. The observed non-linearity with ac-field amplitudes in our system, share some similarities with (111) oriented PbSc 0.5 Nb 0.5 O 3 thin films [28] in which the authors envisioned the system as hybrid polar state, i.e., combination of FE and glassy behavior. However, we also suggest an alternative mechanism that the non-linearity in dielectric response with frequency and ac field amplitude may also have its origin in the interplay between the domain interfaces and pinning defects.…”

“…However, it was shown in literature that the bulk relaxor behavior with ac-and dc-is not encountered in thin films of lead based systems grown on (001) substrates [1,2,9]. Although, a hybrid polar state (both FE and relaxor) sharing its bulk results, is found in (111) oriented PbSc 0.5 Nb 0.5 O 3 thin films [28]. This contrast with the films grown on (001) substrates can be ascribed to non-polar nature of films along the (001) direction stabilizing the relaxor character in those thin films, with no observation to FE transformation with temperature and field [29].…”