Dielectric characteristics and phase structure of lead-free Bi0.5(Na1−x−yKxAgy)0.5TiO3 piezoelectric ceramics

Lead-free piezoelectric ceramics, Bi0.5(Na1−x−yKxAgy)0.5TiO3, were prepared by a solid-state reaction process, and the dielectric property and phase structure of Bi0.5(Na1−x−yKxAgy)0.5TiO3 ceramics were investigated. XRD patterns show that the MPB of BNKAT(x/0.02) system ceramics lies in the composition range of 0.175 ≤ x ≤ 0.20. The relative permittivity ɛr and loss tangent tan δ vary with the K+ content and show a strong temperature- and frequency-dependent behavior in the temperature range measured. The K+ content strongly influences the transition temperature from ferroelectric to anti-ferroelectric phase. In the high-temperature range, the thermal variation of the relative permittivity at various frequencies is well described by the law (1/ɛr) − (1/ɛr,m) = C(T − Tm)α. Such a relaxation behavior may be ascribed to the cations disorder of Na+, K+, Ag+, Bi3+ at A-site.