The relationship between phase structure and electrical properties in (1 - X)(Bi _0.5 Na _0.5 TiO ₃- Ba _0.5 K _0.5 TiO ₃- BaTiO ₃)- x K _0.5 Na _0.5 NbO ₃ quaternary lead-free piezoelectric ceramics

(1 - x)(0.85Bi_0.5Na_0.5TiO₃-0.11Ba _0.5K_0.5TiO₃-0.04BaTiO₃)- xK _0.5Na_0.5NbO₃ lead-free piezoelectric ceramics with x = 0.00, 0.02, 0.03, 0.04, 0.05, and 0.10 were prepared by a conventional solid state method. A coexistence of rhombohedral (R) and tetragonal (T) phases was found in the system, which tended to evolve into pseudocubic symmetry when x increases. The x = 0.04 sample exhibited improved electrical properties: the dielectric constant ε_r = 1900 with the low loss tangents 0.06, the S_max/E_max of ~400 and ~460 pm/V under unipolar and bipolar electric field, respectively. Meanwhile, piezoelectric constant d ₃₃ still maintained ~160 pC/N. These could be owed to the formation of polar nanoregions for relaxor phase.