Lead-free ferroelectric Na0.5Bi0.5TiO3 (NBT), 0.94Na0.5Bi0.5TiO3-0.06BaTiO3 (NBT-6BT) and (Na0.5Bi0.5)0.94Ba0.06(Nb0.05Ti0.95)O3 (Nb-NBBT6) ceramics were synthesized via a multi-ionic sol-gel method process. The effects of Nb on the structural, dielectric and ferroelectric properties were studied. Doped Nb ions distributed uniformly in the Nb-NBBT6 ceramics and shrank the grain sizes of Nb-NBBT6. All NBT, NBT-6BT and Nb-NBBT6 ceramics consisted of the rhombohedral phase and the tetragonal phase according to XRD Rietveld refinements. The dielectric constants of the Nb-NBBT6 ceramics were improved compared to NBT and NBT-6BT below 200 °C. The introduction of Nb ions enhanced the dielectric stability, and the temperature difference between two dielectric peaks increased from 153 °C for NBT to 197 °C for Nb-NBBT6. The remnant polarization (Pr) of Nb-NBBT6 ceramics decreased, but the reduced Ec of 7.01 kV/cm and the maximum polarization of 40.79 μC/cm2 (90 kV/cm) revealed the enhanced ferroelectric property. The temperature-dependent ferroelectric hysteresis loops of Nb-NBBT6 ceramics (65–150 °C) exhibited the largest energy-storage density (W) of 0.399 J/cm3 at 90 °C.
