Nanoindentation behaviour of nano BiFeO3

Bismuth ferrite (BiFeO₃) is a unique magnetoelectric multiferroic that exhibits the coexistence of ferroelectricity and antiferromagnetism at room temperature. This unique combination of properties has pumped a huge surge in current research on BiFeO₃ as a future material for very important technological applications such as magnetic detectors and as an active layer in magnetoelectric memories. For such applications involving miniaturized components and devices, it is essentially important to have an idea of the mechanical integrity of the system at the scale of the microstructure. In spite of the wealth of the literature, however, the attempt to evaluate the mechanical integrity of nano BiFeO₃ at a scale comparable with the local microstructural length scale was almost non-existent. Here we report, possibly for the first time the nanoindentation behaviour of a sol-gel process derived nano BiFeO₃ having particle size of 5-25 nm. The nanoindentation studies were conducted at 100-1000 μN loads on a green pellet annealed at a low temperature of only 300 °C to avoid particle coarsening. The results showed interesting dependence of nanohardness and Young's modulus on the nanoindentation load which could be explained in terms of elastic recovery and plastic deformation energy concepts.