Dielectric and ferroelectric properties of lead-free Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3 ferroelectric ceramics

Ceramics with compositions belonging to the Na0.5Bi0.5TiO3-K0.5Bi0.5TiO3 system were fabricated by conventional ceramics preparation technique. The dielectric constant of all compositions between room temperature and 500 °C shows a strong temperature and frequency dependent behavior. The dielectric constant decreases and its maximum are shifted towards high temperature as the frequency increases. In the high temperature range, the thermal variation of the dielectric constant is well described by the law (1/ε)−(1/εm)=C(T−Tm)γ with γ close to 1.5. Such a relaxation behavior is interpreted in terms of cations disorder due to Na+, K+, Bi3+ at A-site. The P-E hysteresis loops at different temperatures reveal the loops to deform at high temperature as a result of macrodomain breaks into microdomains corresponding to a phase transition from ferroelectric to anti-ferroelectric during the heating process. When the crystalline structure belongs to tetragonal symmetry, the material has anti-ferroelectric characteristic because of the loosely packed A-site cations.