Mesocrystalline SrTiO3/CaTiO3 nanocomposites with 3D heteroepitaxial interfaces, superior piezoresponse and high Curie temperature

Ferroelectric mesocrystalline nanocomposites are promising piezoelectric nanomaterials due to the presence of three-dimensional (3-D) heteroepitaxial interfaces, rendering superior piezoelectric and dielectric responses due to lattice strain at the interface. Herein, we describe the synthesis of mesocrystalline SrTiO3/CaTiO3 (ST/CT) nanocomposites via a two-step topochemical process by using layered titanate H1.07Ti1.73O4·nH2O (HTO), as a precursor, and demonstrate the influence of synthesis parameters on nanostructure, morphology, piezoelectric response and dielectric behavior. The mesocrystalline ST/CT nanocomposites are formed by in-situ topotactic structural transformation, consisting of [110]-oriented ST nanocrystals and [001]-oriented CT nanocrystals with high-density 3-D heteroepitaxial interfaces. The presence of 3-D heteroepitaxial interfaces introduces lattice strain at the interface, leading to an enormously enhanced piezoelectric response with a d33* value of 301 p.m./V. Moreover, the Curie temperature of ST phase is significantly increased from −250 °C to 300 °C by introducing lattice strain. It is demonstrated that the piezoresponse depends on lattice mismatch at heteroepitaxial interfaces and optimal lattice mismatch is found to be ∼3.3%, where the largest lattice strain effect and an expected d33* value of about 450 p.m./V could be achieved. These results demonstrate the potential of lattice strain engineering for high-performance lead-free piezoelectric materials.