High-performance (K,Na)NbO3-based binary lead-free piezoelectric ceramics modified with acceptor metal oxide

Abstract Environmental awareness has led to legislation that restricts lead-containing piezoelectric material use; consequently, lead-free alternatives are urgently sought. Chemical modification of the multiphase piezoelectric system can be used to develop electrical properties of lead-free ceramics with thermal stability. This paper reports lead-free potassium sodium niobate (K, Na) NbO3 (KNN)-based piezoelectric ceramics modified with Fe2O3 and prepared via the solid-state route. The results demonstrate that via the partial substitution of Fe3+ for Nb5+ and Ti4+ ions in the B-sites of the perovskite structure, the polymorphic phase transition (PPT) region at the orthorhombic–tetragonal (O–T) phase boundary can be moved to approximately room temperature and the mass transportation during sintering can be enhanced, thereby promoting homogenous grain growth and increased densification. The substantially diminished polarization anisotropy between the O-T phase boundaries promotes domain wall mobility, which can substantially enhance the piezoelectric properties. An optimal piezoelectric coefficient value of d33 = 246 pC/N, an electromechanical coupling coefficient value of kp = 49%, a dielectric permittivity of er = 1420, a remnant polarization of Pr = 23 μC/cm2 and a high Curie temperature of TC = 343 °C were realized at x = 0.08 mol% of Fe2O3. Due to their enhanced electrical properties and high thermal stability, KNN-based lead-free ceramics doped with low-cost Fe2O3 can replace commercial high-lead-content piezoelectric ceramics.