Phase structure and electrical properties of Yb and Mn co-substituted (K0.48Na0.52)NbO3 lead-free piezoelectric ceramics

Rare-earth and Mn co-substituted KNN-based lead-free piezoelectric ceramics and (1−x)(K0.48Na0.52)NbO3-xYbMnO3 (KNN-xYM) were prepared by a conventional solid-state sintering method. The effects of YM addition on the structure, dielectric, and piezoelectric properties of KNN-xYM ceramics were systematically investigated. With increase of YM content, from the rhombohedral to orthorhombic transition temperature (TR-O) moves close to room temperature against the direction of the orthorhombic to tetragonal transition temperature (TO-T). A polymorphic phase transitions (PPT) between rhombohedral and orthorhombic phases exists at x ∼ 0.01 and the optimum electrical characterization (d33 ∼ 140 pC/N, kp ∼ 0.42, Qm ∼ 214, εr ∼ 634, tan δ ∼ 0.02, and Tc ∼ 386 °C) is also given to the compositions (x = 0.01) around PPT. In addition, KNN-xYM ceramics became a relaxor ferroelectric gradually with increasing YM content. These results indicate that the enhanced piezoelectric properties can be achieved based on the coexistence of rhombohedral and orthorhombic phases.