Synthesis and properties of Bi0.5(Na1−x−yKxAgy)0.5TiO3 lead-free piezoelectric ceramics

Bi0.5(Na1−x−yKxAgy)0.5TiO3 piezoelectric ceramics were prepared by conventional ceramic processes. X-ray diffraction patterns show a pure perovskite structure, indicating that the K+ and Ag+ ions substitute for the Na+ ions in Bi0.5Na0.5TiO3. The temperature dependence of the dielectric constant and dissipation factor shows all ceramics to experience two phase transitions: from ferroelectric to anti-ferroelectric and from anti-ferroelectric to paraelectric. The transition temperature from ferroelectric to anti-ferroelectric and the temperature at which the dielectric constant reaches its maximum value decrease with the increase of K+ amount. At room temperature, the ceramics containing 17.5–20 mol% K+ and 2 mol% Ag+ exhibit high piezoelectric constant (d33 = 180 pC/N) and high electromechanical coupling factor (kp = 35%).