Na0.5K0.5NbO3–BiFeO3 lead-free piezoelectric ceramics

Lead-free (Na0.5K0.5)NbO3-based piezoelectric ceramics were successfully fabricated by substituting with a small amount of BiFeO3 (BF). Difficulty in sintering of pure NKN ceramics can be eased by adding a few molar percent of BF, and the crystalline structure is also changed, leading to a morphotropic phase boundary (MPB) between ferroelectric orthorhombic and rhombohedral phases. The MPB exists near the 1–2 mol% BF-substituted NKN compositions, exhibiting enhanced ferroelectric, piezoelectric, and electromechanical properties of Pr=23.3 μC/cm2, d33=185 pC/N, and kp=46%, compared to an ordinarily sintered pure NKN ceramics. The MPB composition has a Curie temperature of ∼370 °C, comparable to that of some commercial PZT materials.