Phase transition behavior and electrical properties of lead-free (1-x)KNLNS-xBNKZ piezoelectric ceramics

Lead-free (1-x)(K_0,48Na_0,48Li_0,04)(Nb_0,95Sb_0,05)O₃-xBi_0.5(Na_0.82K_0.18)_0.5ZrO₃ (KNLNS-xBNKZ) piezoelectric ceramics (x?=?0, 0.02, 0.04, 0.06, 0.08, and 0.1) were successfully prepared by the two-step sintering method. The effects of different BNKZ contents on the crystal structure, ferroelectric phase transition, and electrical properties of the as-prepared ceramics were systematically researched. The ceramics with a perovskite structure possessed an orthorhombic phase (space group?=?Amm2) at x?=?0, a mixed orthorhombic-tetragonal phase (Amm2?+?P4/mbm) at x?=?0.02, a mixed rhombohedral-tetragonal (R-T) phase (R3m?+?P4/mbm) at x?=?0.04–0.06, and a rhombohedral phase (R3m) at x>0.06. At x?=?0.04 (rhombohedral and tetragonal (R-T) phases coexisted), the ceramics manifested the best electrical properties with d₃₃?=?224 pC/N, k_p = 0.44, k_t = 0.47, T_C = 218^oC, and remanent polarization (P_r)?=?11.5µC/cm². The improvement of the electrical properties of KNLNS-BNKZ ceramics was achieved by controlling their phase compositions and microstructures.