Polymorphic phase transition-induced electrical behavior of BiCoO3-modified (K0.48Na0.52)NbO3 lead-free piezoelectric ceramics

(1 − x)(K0.48Na0.52)NbO3-xBiCoO3 [KNN-xBC] lead-free piezoelectric ceramics were prepared by the conventional solid-state sintering method. The effects of the BiCoO3 addition on the phase structure, dielectric, piezoelectric and ferroelectric properties of KNN-xBC ceramics were systematically investigated. The polymorphic phase transition (PPT) from rhombohedral to orthorhombic phase around room temperature was identified in the composition range of 0.01 ≤ x ≤ 0.02, and the improved electrical properties were induced by this PPT. The KNN-0.01BC ceramics near PPT exhibit optimum electrical properties: d33 ∼ 165 pC/N, kp ∼ 0.40, Pr ∼ 31.0 μC/cm2, and Ec ∼ 12.6 kV/cm. These results indicate that the enhanced piezoelectric properties for alkali niobate can be achieved by forming the coexistence of rhombohedral and orthorhombic phases.

► (1-x)(K0.48Na0.52)NbO3-xBiCoO3 were prepared by conventional solid-state sintering method ► Polymorphic phase transition (PPT) from rhombohedral to orthorhombic phase ► Improved electrical properties were induced by the PPT, with the composition range 0.01≤ x ≤0.02 ► KNN-0.01BC ceramics show good properties: d33∼165 pC/N, kp∼0.40, Pr∼31.0 μC/cm2, Ec∼12.6 kV/cm