B-site doping as a strategy for tailoring BiFeO3 properties

Abstract

Ferroelectric, magnetic and structural properties of BiFe1–xNbxO3 (x = 0.002, 0.005 and 0.01) ceramics were investigated in order to study the influence of B-site doping of multiferroic BiFeO3. It is known that pure BiFeO3 exhibits G-type of antiferromagnetism below Néel temperature (TN = 370 °C) and spontaneous polarization along one of the eight pseudo-cubic [111] axes below Curie temperature (TC = 826–845 °C). However, poor ferroelectric (high electrical conductivity) and weak ferromagnetism of pure BiFeO3 can be enhanced by doping. In this study, Nb5+ was introduced to replace Fe3+ (B-site doping) since it could disturb the nearly antiparallel spin ordering of the adjacent Fe3+ ions responsible for cycloidal (spiral) spin structure. On the other hand, the pentivalent Nb cations will reduce the amount of oxygen vacancies and consequently reduce the electrical conductivity. It was shown that 1 % Nb drastically changed the magnetic properties compared with pure BiFeO3: while the remnant magnetization at 300 K reaches only 0.0042 emu/g at applied magnetic fields up to 50 000 Oe, the coercive magnetic field as high as ~7460 Oe classifies BiFe0.99Nb0.01O3 as hard magnetic material. With lower Nb content the magnetic properties moved up towards the properties of pure BiFeO3. Relatively inferior ferroelectric properties showed the sample with 0.2 % Nb, since its hysteresis loops deformed at electrical fields higher than 40 kV/cm. At the highest applied electrical field (70 kV/cm) only the sample with 1 % Nb showed a stable ferroelectric response with hysteresis periods up to 1000 ms, with the highest remnant electrical polarization of 0.5 μC/cm2 and the coercive electrical field of 22.2 kV/cm. Thus, it was shown that by carefully selected dopant it was possible to improve both magnetic and ferroelectric properties of BiFeO3.