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

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