Biphasic BiFeO3 ceramics based on rhombohedral and tetragonal polymorphs

ABSTRACT From a new perspective, polymorphism is now often considered as a functional property that extends the applications of many materials. BiFeO3 is still an interesting material from both fundamental and applied points of view. A unique characteristic of BiFeO3 film, the polymorphism was stabilised only using the epitaxial strain caused by the substrate of the film. Here we report the hydrothermal synthesis of biphasic BiFeO3 ceramics using low NaOH concentration and temperature. The ability of BiFeO3 ceramics to morph into tetragonal and rhombohedral allotropic phases was demonstrated, confirming the theoretical prediction that the polymorphism can be stabilised even in powder form. Based on our experimental study NaOH(aq) is proposed as responsible for the strain on the structure of the rhombohedral phase. In addition, the in-depth characterisation of this biphasic ceramic opens up new opportunities for the technological applications of BiFeO3 material.