Thermally enhanced piezoelectricity via the superstructure in Ca2Nb2O7 single-crystals with ultra-high Curie temperature

Abstract

Due to the requirements of sustainable development and the widening application range, it is very necessary to develop lead-free eco-friendly piezoelectric materials with ultra-high Curie temperatures (T_c). The perovskite-like layered structure (PLS) Ca₂Nb₂O₇ is considered a potential candidate with ultra-high T_c (1773 K). Herein, we prepared Ca₂Nb₂O₇ single-crystals by the optical floating zone (OFZ) method. The piezoelectric constant d₃₃ of Ca₂Nb₂O₇ along the b-axis reaches 10.4 pC N⁻¹ at room temperature and the d₃₃ is enhanced to 15.2 pC N⁻¹ when the temperature increases from 273 to 750 K. Furthermore, the origin of piezoelectricity as well as the mechanism of the orientation-dependent and thermally enhanced d₃₃ of Ca₂Nb₂O₇ were clarified based on the microstructure, lattice structure, and vibration by completely characterizing the corresponding parameters.