Biocompatible ferroelectric (Na,K)NbO3 nanofibers

Dense homogeneous textile composed from continuous bead-free sodium potassium niobate (NKN) nanofibers 100 μm long and 50-200 nm in diameter was sintered by sol-gel calcination assisted electrospinning. High resolution electron microscopy and x-ray diffraction revealed preferential cube-on-cube growth of fibers in [001] direction. Raman spectrum of NKN fibers contains all the features characteristic to electrically poled orthorhombic phase. In contrast to polycrystalline ceramics, it shows relative enhancement of the Raman cross section of isotropic A1g(ν1) mode compared with polar axis defined F2g(ν5) and Eg(ν2) vibrations. We interpret this as an evidence for superparaelectric state of NKN nanofibers. Spontaneous polarization inside highly crystalline nanofiber exists at room temperature though big distance between fibers prevents the settling of a net macroscopic polarization.