Impressive Nanogenerator Application Using Nanoscale LuFeO₃: Role of Structure and Morphology

In the domain of multiferroicity, Lutetium orthoferrite (LuFeO₃) represents a<br/>potentially interesting material owing to the fact that it exhibits orthorhombic (o) and hexagonal (h)<br/>structures, which significantly differ in terms of lattice symmetry and the symmetry of the surroundings<br/>of the individual cations. This difference in structural symmetry contributes to unusual changes in<br/>physical properties. In o-LFO canting of Fe moments towards c direction gives rise to weak<br/>ferromagnetism below Néel Temperature (620 K), while, ferroelectricity is unexpected due to<br/>symmetry of lattice. On the other hand, weak ferromagnetism is not allowed in h-LFO unless the<br/>moments are along the ‘a’ axis. Present work is intended to realize the co-existence of o-LFO and h-<br/>LFO to achieve ferroelectricity and ferromagnetism simultaneously in a single nanostructure of two<br/>different morphologies i.e. nanoparticles and nanofibers. In multiferroic LuFeO₃ the hexagonal (-h)<br/>phase is an intermediate metastable phase encountered during the amorphous to orthorhombic (-o)<br/>transformation and is ferroelectric in nature. So far h-phase has only been stabilized in a substrate-<br/>supported layered ultrathin film form. Herein we show that the surface-induced strain field intrinsically<br/>present in nano-systems can self-stabilize this phase and the hexagonal to orthorhombic phase<br/>constitution ratio depends on the shape of the nanomaterial. Thus, nanofibers (nanoparticles) strain-<br/>stabilize the o : h ratio of about 23 : 77 (75 : 25). The inclusion of nano-LuFeO₃ into PDMS renders<br/>impressive nanogenerator performance, consistent with the ferroelectric phase content. This trait in the<br/>biphasic LuFeO₃ is attributed to: (i) Structure: Orthorhombic and hexagonal mixed phase: wherein the<br/>lattice dynamics change with temperature (both in case of nanoparticles and nanofibers), (ii)<br/>Morphology: (nanoparticles and nanofibers): wherein the dynamics of interparticle interactions would<br/>differ for nanoparticles and nanofibers.