Enhanced piezoelectric and energy storage performance of 0.96(K0.48Na0.48Li0.04)(Nb0.95Sb0.05)O3–0.04Bi0.5(Na0.82K0.18)0.5ZrO3 ceramics using two-step sintering method

The 0.96(K 0.48 Na 0.48 Li 0.04 )(Nb 0.95 Sb 0.05 )O 3 –0.04Bi 0.5 (Na 0.82 K 0.18 ) 0.5 ZrO 3 (KNLNS–BNKZ) lead-free ceramics were successfully synthesized by combining the conventional mixed-oxide method with the two-step sintering method. The influence of two-step sintering parameters (including sintering temperature, T 2 , and time, t 2 ) on the phase structure, dielectric, ferroelectric, piezoelectric, and energy storage properties of KNLNS–BNKZ ceramics is studied. X-ray diffractograms (XRD) revealed a pure perovskite structure, consisting of a mixed phase of rhombohedral–tetragonal (space group: R 3 m + P 4 /mbm ) crystal structure in all the ceramics, irrespective of variation in sintering temperature and time. However, the second phase (K 6 Nb 10.8 O 30 ) appeared when the sintering time is ≥ 6 h. Corresponding to optimized two-step sintering parameters, electrical properties of KNLNS–BNKZ ceramics are best: the density ( ρ ) of 4.45 g/cm 3 , the electromechanical coupling factor ( k p ) of 0.51, ( k t ) of 0.55, the piezoelectric constant ( d 33 ) of 251 pC/N, and the remanent polarization ( P r ) of 16.77 µC/cm 2 were obtained at T 2 = 1060 °C and t 2 = 5 h, proving the efficacy of two-step sintering technique. Especially, the optimal sintering conditions for KNLNS–BNKZ ceramics resulted in enhanced energy storage density of 200% and an energy storage efficiency of 51.8%, respectively.