Piezoelectric and ferroelectric properties of (Bi1−xNa0.8K0.2Lax)0.5TiO3 lead-free ceramics

Lead-free piezoelectric ceramics (Bi1−xNa0.8K0.2Lax)0.5TiO3 were synthesized successfully by conventional solid state reaction method. The piezoelectric, dielectric and ferroelectric characteristics of the ceramics were investigated and discussed. The XRD results show that La3+ has diffused into (BiNa0.8K0.2)0.5TiO3 (BNKT) lattices to form a new solid solution (Bi1−xNa0.8K0.2Lax)0.5TiO3 with a pure perovskite structure. Partial substitution of La3+ for Bi3+ in the BNKT ceramics can enhance their piezoelectric, without an obvious decline of ferroelectric properties. The piezoelectric measurements and P–E hysteresis loops reveal that the ceramic with x = 0.005 has the highest piezoelectric performance and strong ferroelectricity. At high La3+ level (x > 0.04), the low dielectric anomaly at Td disappears. A maximum strain of 0.16% is obtained at x = 0.02 for the (Bi1−xNa0.8K0.2Lax)0.5TiO3 ceramic. The depolarization temperature Td decreases with x increasing (x = 0–0.08), and the depolarization mechanism is analyzed.

► Moderate La substitution enhances the piezoelectric properties of the ceramics. ► A maximum strain of 0.16% is achieved with a low field. ► A large piezoelectric response is achieved in (Bi0.995Na0.8K0.2La0.005)0.5TiO3. ► Depolarization mechanism is analyzed.