Fabrication of Lead-Free (Na_0.52K_0.44Li_0.04)(Nb_0.84Ta_0.10Sb_0.06)O₃ Piezoelectric Ceramics by a Modified Solid-State Reaction Method

(Na_0.52K_0.44Li_0.04)(Nb_0.84Ta_0.10Sb_0.06)O₃ (LF4) ceramics have been successfully prepared by a combination of a modified solid-state reaction and a conventional sintering method. LF4 fine powder with a perovskite structure was obtained by the modified solid-state reaction and continuous re-calcination treatment at low temperatures of 500–600 °C. The obtained fine powders had good sinterability and high-density LF4 ceramics with relative density more than 94% could be easily obtained by a conventional sintering. The obtained LF4 ceramics showed excellent piezoelectricity. The Curie temperature of LF4 ceramics was about 280 °C. The leak current measurements exhibited that the insulation property of the LF4 was improved by sintering in the oxygen atmosphere due to the decrease in the oxygen vacancies. The LF4 ceramics sintered in the oxygen atmosphere, which showed a larger saturated P–E hysteresis loop, also showed larger piezoelectricity than those sintered in the air. Additionally, we found that the LF4 ceramics after P–E hysteresis measurement exhibited larger piezoelectric properties than those without P–E hysteresis measurement. The largest piezoelectric constant d₃₃ was 352 pC/N and the planar electromechanical coupling factor k_p was 44%. This would be due to the effect on the domain motion by applying an AC bias field.