Synthesis of Monoclinic Potassium Niobate Nanowires That Are Stable at Room Temperature

We report the synthesis of KNbO3 nanowires
(NWs) with
a monoclinic phase, a phase not observed in bulk KNbO3 materials.
The monoclinic NWs can be synthesized via a hydrothermal method using
metallic Nb as a precursor. The NWs are metastable, and thermal treatment
at ∼450 °C changed the monoclinic phase into the orthorhombic
phase, which is the most stable phase of KNbO3 at room
temperature. Furthermore, we fabricated energy-harvesting nanogenerators
by vertically aligning the NWs on SrTiO3 substrates. The
monoclinic NWs showed significantly better energy conversion characteristics
than orthorhombic NWs. Moreover, the frequency-doubling efficiency
of the monoclinic NWs was ∼3 times higher than that of orthorhombic
NWs. This work may contribute to the synthesis of materials with new
crystalline structures and hence improve the properties of the materials
for various applications.