Rhombohedral–orthorhombic phase coexistence and electrical properties of Ta and BaZrO3 co-modified (K, Na)NbO3 lead-free ceramics

• An R–O boundary of KNN ceramics is constructed by the addition of BaZrO3 and Ta.
• The ceramic with x = 0.06 has d33 ∼ 193 pC/N and kp ∼ 32.6%.
• An R–O phase boundary is an effective way to improve the d33 of KNN-based ceramics.

The BaZrO3 and Ta have been used to improve piezoelectric properties of (K, Na)NbO3 ceramics by the construction of the phase boundary, and (1 − x)K0.48Na0.52(Nb0.95Ta0.05)O3–xBaZrO3 [(1 − x)KNNT–xBZ] ceramics were prepared by the conventional solid-state method. The effect of BZ content on their phase structure, microstructure, and electrical properties has been investigated. A rhombohedral and orthorhombic phase coexistence has been observed in the compositional range of 0.05 ≤ x ≤ 0.07. With increasing BZ content, their Tc and To–t values decrease gradually, and the dielectric constant increases linearly. The ceramic with x = 0.06 exhibits an enhanced piezoelectric behavior (d33 ∼ 193 pC/N and kp ∼ 32.6%) because of the coexistence of two phases together with a dense microstructure. As a result, the construction of a rhombohedral and orthorhombic phase boundary is an effective way to improve the piezoelectric properties of KNN-based ceramics.