Optimization of the calcination and two-step sintering temperatures of (K0.48Na0.48Li0.04)(Nb0.95Sb0.05)O3 ceramics

Lead-free (K0.48Na0.48Li0.04)(Nb0.95Sb0.05)O3 (KNLNS) ceramics have been successfully optimized for the calcination and two-step sintering temperatures. The experimental results reveal that the KNLNS powder calcined at 850 or 900 °C presented a pure perovskite phase with an orthorhombic phase. The particle size was in the range of 0.1–0.4 μm. The two-step sintering temperature (range: 950 to 1100 °C) significantly affects the structure, microstructure, and electrical properties of KNLNS ceramics. The presence of a pure perovskite phase with good crystallization is observed in all samples. The microstructure was researched by varying the two-step sintering temperature to obtain a dense microstructure and a clear grain boundary in order to optimize their piezoelectric properties. The best electrical properties of KNLNS ceramics were recorded at the optimized temperature of 1050 °C (density (ρ): 4,35 g cm−3; electromechanical coupling factor (kp): 0.33, kt: 0.35; dielectric constant (εr): 849; dielectric loss (tanδ): 0.073; maximum dielectric constant (εmax at TC): 6659; piezoelectric constant (d33): 195 pC N−1; remanent polarization (Pr): 16.1 μC cm−2; energy storage density (Wrec): 0.36 J cm−3; energy storage efficiency (η): 48.1%; t2 = 4 h), proving the efficacy of the two-step sintering technique.