Engineering grain orientation and local heterogeneous enable further breakthroughs in piezoelectricity for NaNbO₃-based piezoelectric oxides

Eco-friendly NaNbO3 (NN)-based relaxor ferroelectric ceramics with high dielectric constants cannot meet the high piezoelectric activity quality factors (FOMs: d(33) x g(33)) requirements of electromechanically coupled devices. To solve this issue, we successfully improved the piezoelectricity of NN-based relaxor piezoceramics while reducing the dielectric constant based on microstructural tuning by virtue of the chemical design and texturing engineering. Mainly affected by the highly <001>c orientation and relaxor MPB, the obtained novel 88.5NaNbO(3)-10Ba(Ti0.7Sn0.3)O-3-1.5NaSbO(3) texture ceramics enjoys an ultrahigh piezoelectric coefficient (d(33) = 423 pC/N), reaching a record high in NaNbO3-based lead-free ceramics. Meanwhile, a large FOMs value (d(33) x g(33) = 13.310(-12) m(2)/N) is successfully realized due to the suppression of the dielectric constant. More importantly, the stable phase/domain evolution also encourages excellent temperature stability for piezoelectricity and FOMs. Especially for the piezoelectricity, when the annealing temperature is < 140 degrees C, the d(33) of the 1.5T ceramics can be stabilized similar to 400 pC/N. Such excellent electrical temperature stability shows more competition in the reported NN-based piezoceramics. This work not only provides a design paradigm for high-performance piezoelectric materials, but also facilitates their development in electromechanical coupling devices.