Phase boundary design and enhanced electrical properties in (Bi0.5Li0.45Ag0.05)(Zr0.98Hf0.02)O3-modified KNN-based lead-free piezoceramic

For fabricating (K, Na)NbO3-based ceramic, the improved piezoelectric properties can be obtained through phase boundary design. Herein, the (1 − x)K0.48Na0.52Nb0.96Sb0.04O3–x(Bi0.5Li0.45Ag0.05)(Zr0.98Hf0.02)O3 lead-free ceramics with rhombohedral-tetragonal (R-T) phase boundary was designed and developed by the conventional pressureless sintering. The relationship between phase structure, surface morphology and electrical properties was systematically investigated. According to phase diagram from XRD and dielectric-temperature measurements, the ceramics exhibit the R-T phase coexistence in the range of 0.035 ≤ x ≤ 0.05. As a result, the optimal comprehensive properties (d33 ~ 343 pC/N, d33* ~ 410 pm/V, TC ~ 270 °C) were achieved in the ceramic with x = 0.035, due to the coexistence of R-T phase caused free energy flatten and energy barrier reduce. These results indicate that the construction of R-T phase coexistence is an effective strategy to improve the electrical properties of KNN-based ceramics.