Flash sintering of BiFeO3 ceramics

Magnetoelectric multiferroics with coupled ferroelectricity and ferromagnetism have potential applications to construct new forms of multifunctional devices. Among the few known single-phase multiferroics, the bismuth-iron... [ view full abstract ]

Magnetoelectric multiferroics with coupled ferroelectricity and ferromagnetism have potential applications to construct new forms of multifunctional devices. Among the few known single-phase multiferroics, the bismuth-iron oxide, BiFeO₃, is one of the most promising. Unfortunately, the properties of pristine BiFeO₃ materials are still not suitable for the fabrication of multiferroic devices: a high electrical conductivity and the absence of a net magnetic response usually hamper their practical applications. The most accepted strategy to overcome these drawbacks and eventually enhance the functional response of BiFeO₃-based multiferroics is doping. Particularly, Ti⁴⁺-doping is very encouraging to both decrease the leakage current and provide a ferromagnetic-like behavior. On the other hand, in addition to the issues regarding the intrinsic functional response, the processing of these materials is also tricky and usually results in products that contain a certain amount of unwelcome secondary phases. Although BiFeO₃ ceramic powders with suitable phase purity may be prepared by meticulously controlling the synthesis conditions, even in these cases the situation may be further reverted during the consolidation of the synthesized powders. The reasons for the difficulties in sintering BiFeO₃ lie in the fact that, besides the general requirements of controlling the equilibrium between densification and coarsening, additional problems related with the synthesis complexity, bismuth volatilization and the low thermal stability of the pure compound are to be faced. Visibly, the prospect of preparing BiFeO₃-based ceramics by alternative low-temperature sintering techniques would be greatly welcome to avoid these difficulties. In the present work, we have explore the possibility of consolidating undoped and Ti⁴⁺-doped BiFeO₃ ceramics by an electric current assisted sintering (ECAS) technique. The effect of the dopant on the electric and thermal conditions that lead to the flash sintering of these materials have been studied. Besides, the microstructural features developed under different electric conditions have been thoroughly investigated.