Boosted piezoelectricity with excellent thermal stability in tetragonal NaNbO₃-based ceramics

The realization of high piezoelectric performance and excellent temperature stability simultaneously in Pb-free ceramics is the key for replacing Pb-containing perovskites in the industry. In this study, large piezoelectric performance (d₃₃ = 354 pC N⁻¹) was achieved in a wide temperature sinterable potassium-free NaNbO₃-BaTiO₃-BaSnO₃ system, which is twice more than the piezoelectricity found in NaNbO₃-BaTiO₃ binary ceramics. Structural refinement of high-energy synchrotron powder diffraction data suggests a single tetragonal structure with P4bm symmetry for the studied NaNbO₃-based Pb-free ceramic. The results indicate that the small axial ratio favoring polarization reorientation benefits strong piezoelectricity, while the large oxygen octahedron tilt enhances the stability of the P4bm structure during the changing temperature according to the in situ high-energy synchrotron X-ray diffraction measurements and provides the foundation for the excellent thermal stability (20-100 °C) of the piezoelectric properties. A single tetragonal phase with a tiny axial ratio and large oxygen octahedron tilt effectively balances the piezoelectricity and thermal stability in Pb-free systems.