Unleashing the Electromechanical Response of Ferroelastic Domain Reorganization in Mixed-Phase Tetragonal...

There is considerable interest in thin-film electromechanical materials due to the prospect for device miniaturization for an array of applications. The electromechanical response of thin films, however, is generally limited by substrate clamping and electrical breakdown. This work designs thin-film piezoceramics with sub-100-nm thickness that address the limitations of clamping and breakdown strength and, as a result, produces films that rival or surpass their bulk piezoceramics counterparts in terms of performance. In the tetragonal ferroelectric PbZr_0.2Ti_0.8O₃, strain-induced mixtures of in- and out-of-plane oriented domain structures are leveraged to achieve the ferroelastic interconversion of in-plane-polarized a domains to out-of-plane-polarized c domains, opening a pathway to enhanced electromechanical response (1.25%, $d_{33}^{\mathrm{eff}}$ = 170 pm/V). Operando second harmonic generation and scanning transmission electron microscopy studies confirm the a-to-c ferroelastic conversion, and establish the switching from a₁/a₂ to c/a superdomains as the underlying mechanism for the large response. In turn, PbZr_0.2Ti_0.8O₃/0.68PbMg_1/3Nb_2/3O₃-0.32PbTiO₃/PbZr_0.2Ti_0.8O₃ trilayers are fabricated to improve the electrical-breakdown strength while maintaining the domain-structure interconversion, resulting in the enhancement of the electromechanical strain to 2.1%. Overall, by combining domain-structure optimization and multilayer-heterostructure design, remarkable electromechanical response can be achieved even in sub-100-nm thin films normally subject to clamping effects.