Enhancement of Piezoelectric Performance of Lead‐Free NKN ‐Based Ceramics via a High‐Performance Flux— NaF – Nb 2 O 5

x ( NaF −0.5 Nb 2 O 5 )−(1 −  x )[( Na 0.5 K 0.5 )( Nb 0.8 Ta 0.2 ) O 3 ] (100 x NN − NKNT ) piezoelectric ceramics were fabricated to high densities above 97% when sintering at temperatures ~1200°C. Compared with pure ( Na , K ) NbO 3 ( NKN ), dielectric constants of the NaF – Nb 2 O 5 flux‐doped NKNT ceramics were increased whereas dielectric losses remained low. High field polarization switching showed very square hysteresis loops, but the coercive fields were decreased through a “softening” doping effect induced by the flux. A R ayleigh analysis inferred that the extrinsic contribution from the domain wall dynamics was increased with the flux addition. Collectively, all the experimental observations suggested that NaF – Nb 2 O 5 was, in part, soluble in the structure and highly suitable for obtaining a stable NKN system with improved piezoelectric performance.