Optimization of the calcination and two-step sintering temperatures of (K_0.48Na_0.48Li_0.04)(Nb_0.95Sb_0.05)O₃ ceramics

Lead-free (K_0.48Na_0.48Li_0.04)(Nb_0.95Sb_0.05)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 (k _p ): 0.33, k _t: 0.35; dielectric constant (ϵ _r ): 849; dielectric loss (tanδ): 0.073; maximum dielectric constant (ϵ _max at T _C): 6659; piezoelectric constant (d ₃₃): 195 pC N⁻¹; remanent polarization (P _r ): 16.1 μC cm⁻²; energy storage density (W _rec): 0.36 J cm⁻³; energy storage efficiency (η): 48.1%; t ₂ = 4 h), proving the efficacy of the two-step sintering technique.