Phase Coexistence Induced Giant Dielectric Tunability and Electromechanical Response in PbZrO Epitaxial Thin Films.

PbZrO (PZO) thin films, as a classic antiferroelectric material, have attracted tremendous attention for their excellent dielectric, electromechanical, and thermal switching performances. However, several fundamental questions remain unresolved, particularly the existence of an intermediate phase during the transition from the antiferroelectric (AFE) to ferroelectric (FE) state. Here, a phase coexistence configuration of an orthorhombic AFE phase and a tetragonal-like (T-like) phase is reported in epitaxial antiferroelectric PZO thin films, with thickness ranging from 16 to 110 nm. This configuration is evidenced both macroscopically by distinct shoulder-cape-shaped dielectric behavior and microscopically through scanning transmission electron microscopy (STEM) analysis. Remarkably, a 49 nm PZO film achieves an ultrahigh dielectric tunability of 90.1%, while a 59 nm film exhibits significant electromechanical strain of 0.66%. Microscopically, HAADF-STEM reveals the presence of the intermediate phase with a dipole arrangement of vertically diagonal up-up-down-down pattern, and first-principles calculations further confirm the role of this intermediate phase during AFE-to-FE phase transition, which is responsible for the unusual dielectric peaks of ɛ-E curves. These findings not only enhance the understanding of phase transition in antiferroelectric materials but also exhibit great potential for high-performance tunable and nano-electromechanical device applications.