Characterization of relaxor ferroelectrics from BiFeO₃ doped (K_0.5Na_0.5)NbO₃ systems

The additon of BiFeO₃ (BFO) to (K_0.5Na_0.5)NbO₃ (KNN) systems and termed as (l-x)KNN-xBFO for x=0 and x=0.075 were successfully synthesised using a combination of solid-state reaction and auto-combustion methods. The single phase of KNN-BFO was formed by two step of heat threatments; it is calcined at 575 °C for 6h then sintered at 1100 °C for 6h. The phase structure of KNN material changes from the orthorombic symmetry to tetragonal symmetry after the addition of BFO. The relaxor ferroelectric properties were carried out using impedance analyzer at various temperature and frequency. The pure KNN shows a typical ferroelecrics that has two Curie temperature at 220 °C (orthorombic-tetragonal transition) and 440 °C (tetragonal-cubic transition). After the 7.5%mol.BFO doped in the KNN system, the maxima peak around Tc becomes broader and its transition temperature becomes invisible then has a relaxor behaviours. The Currie-Weiss law is used to prove the ferroelectric of KNN (γ≤1) and relaxor of KNN-BFO (γ≥1).