Three‐State Ferroelastic Switching and Large Electromechanical Responses in PbTiO₃ Thin Films

Abstract

Leveraging competition between energetically degenerate states to achieve large field-driven responses is a hallmark of functional materials, but routes to such competition are limited. Here, a new route to such effects involving domain-structure competition is demonstrated, which arises from strain-induced spontaneous partitioning of PbTiO thin films into nearly energetically degenerate, hierarchical domain architectures of coexisting c/a and a /a domain structures. Using band-excitation piezoresponse force microscopy, this study manipulates and acoustically detects a facile interconversion of different ferroelastic variants via a two-step, three-state ferroelastic switching process (out-of-plane polarized c → in-plane polarized a → out-of-plane polarized c state), which is concomitant with large nonvolatile electromechanical strains (≈1.25%) and tunability of the local piezoresponse and elastic modulus (>23%). It is further demonstrated that deterministic, nonvolatile writing/erasure of large-area patterns of this electromechanical response is possible, thus showing a new pathway to improved function and properties.

Understanding the Role of Ferroelastic Domains on the Pyroelectric and Electrocaloric Effects in Ferroelectric Thin Films

“…In such films, both phenomenological and phase‐field models as well as experiments have shown a systematic evolution from a monodomain and purely out‐of‐plane polarized c‐ domain structure at large compressive strains, to a polydomain c / a‐ domain structure (with c and a domains coexisting as alternate bands) at moderate compressive and tensile strains. Increasing the tensile strain further results in a recently observed mixed‐phase coexistence of both c / a ‐ and a 1 / a 2 ‐domain structures before a complete transition to the fully in‐plane polarized a 1 / a 2 ‐domain structure is achieved under high tensile strains ( Figure a) . Depending upon the strain regime, the effect of temperature on the domain structures can be broadly classified into four categories, 1) within the pure c phase, the monodomain structure present at room temperature is preserved upon heating (shaded in orange, Figure a); 2) within the c / a phase, increasing the temperature drives an increase in the fraction of c ‐oriented domains (shaded in yellow, Figure a); 3) within the mixed phase, where there is a coexistence of c / a ‐ and a 1 / a 2 ‐domain structures, increasing the temperature drives an increase in the fraction of a 1 / a 2 at the expense of the c / a ‐domain structure (shaded in light green, Figure a); and 4) within the a 1 /a 2 phase, the completely in‐plane polarized domain structure is preserved with increasing temperature (shaded in dark green, Figure a).…”

“…Primarily, this has been achieved by placing a material in the vicinity of a phase transition driven either by chemistry or temperature where most ferroic susceptibilities diverge. More recently, advances in the growth of ferroic thin films has shown that epitaxial strain can be another route by which to manipulate ferroelectric order, ferroic susceptibilities, and domain structures . In turn, there has been extensive work in understanding the role of such ferroelectric/ferroelastic domains and domain walls on the dielectric and piezoelectric response.…”

Constructing Polymorphic Nanodomains in BaTiO3 Films via Epitaxial Symmetry Engineering

“…Inspired by the rapid advancements in heteroepitaxy techniques, recent efforts have been devoted to seeking alternative simple methods to achieve a similar polymorphic or energy‐degenerated nanodomain state in epitaxial ferroelectric oxide thin films. [ 4,13–15 ] One of the most important and successful strategy is strain engineering. For example, it was reported that appropriate epitaxial strain can position BiFeO 3 films on a boundary between rhombohedral and tetragonal phases.…”

Intrinsic Dipole Coupling in 2D van der Waals Ferroelectrics for Gate‐Controlled Switchable Rectifier

“…[3,15] According to previous theoretical and experimental studies, the Se atomic plane in the central layer could be vertically and laterally shifted by applying an external electric field. [3,15] According to previous theoretical and experimental studies, the Se atomic plane in the central layer could be vertically and laterally shifted by applying an external electric field.…”

“…[1][2][3][4] The vdWs 2D ferroelectrics have no physical limit of critical thickness, which has been the main issue in conventional ferroelectric films. [1][2][3][4] The vdWs 2D ferroelectrics have no physical limit of critical thickness, which has been the main issue in conventional ferroelectric films.…”