Epitaxial PbZr x Ti 1− x O 3 Ferroelectric Bilayers with Giant Electromechanical Properties

Giant electromechanical response viaferroelastic domain switching is achieved in epitaxial (001) ferroelectric tetragonal (T) PbZr 0.3 Ti 0.7 O 3 /rhombohedral (R) PbZr 0.55 Ti 0.45 O 3 bilayers, grown on La 0.67 Sr 0.33 MnO 3 buffered SrTiO 3 substrates. X‐ray diffraction and transmission electron microscopy show that the domain structure of the T films is tuned as a function of its thickness, from a fully a 1 /a 2 ‐domains (30 nm thick T layer) to a three domain stress‐free c/a 1 /c/a 2 polytwin state (100 nm thick T layer). A large switchable polarization is found up to 65 μC cm −2 . Quantitative piezoelectric force microscopy reveals enhanced piezoelectric coefficients, with d 33 coefficients ranging from 250 to 350 pm V −1 , which is up to seven times higher than the nominal PbZr x Ti 1−x O 3 thin film values. These are attributed to the motion of nanoscale ferroelastic domains. Fatigue testing proves that these domains are reversible and repeatable up to 10 7 cycles. In‐situ X‐ray synchrotron measurements reveal that the ferroelastic domain switching is promoted by a pulsating strain effect imposed by the R layer. The study reports a fundamental understanding of the origin of giant piezoelectric coefficients in epitaxial ferroelectric bilayers.