Structure, dielectric and ferroelectric properties of 0.92Na0.5Bi0.5TiO3–0.06BaTiO3–0.02K0.5Na0.5NbO3 lead-free ceramics: Effect of Co2O3 additive

Abstract 0.92Na 0.5 Bi 0.5 TiO 3 –0.06BaTiO 3 –0.02K 0.5 Na 0.5 NbO 3 + x wt% Co 2 O 3 (NBKT– x Co, x =0, 0.2, 0.4, 0.6, 0.8) lead-free ferroelectric ceramics were prepared via a conventional solid state reaction method. Effects of Co 2 O 3 additive on crystallite structure, microstructure, dielectric and ferroelectric properties of the NBKT– x Co ceramics were studied. X-ray diffraction results showed that the rhombohedral–tetragonal morphotropic phase boundary existed in all the ceramics, with relative amount of tetragonal phase varying with the content of Co 2 O 3 . Average grain size, maximum value of dielectric constant, Curie temperature and ferroelectric properties of the ceramics were close related to the content of Co 2 O 3 . The dielectric anomaly caused by the phase transition between the ferroelectric phase and the so-called “intermediate phase” was observed in the ceramics with x ≤0.2, while it disappeared with further increasing x . All the ceramics showed a diffuse phase transition between the “intermediate phase” and the paraelectric phase. The change in the ferroelectric properties with changing the content of Co 2 O 3 was discussed by considering the competitive effects among grain size, relative amount of the tetragonal phase and oxygen vacancies.