Properties of PVA/HfO2 Hybrid Electrospun Fibers and Calcined Inorganic HfO2 Fibers

New organic−inorganic hybrid fibers (polyvinyl alcohol (PVA)/HfO 2 ) were prepared by an electrospinning method using DI water as a solvent. The HfO 2 −acetate nanoparticles could be loaded up to 80% by weight in PVA polymer to fabricate uniform PVA/HfO 2 electrospun hybrid fibers. After annealing at 140 °C for 12 h, electrospun PVA/HfO 2 fibers were stable when soaked in water. Calcination of these hybrid fibers at temperatures ranging from 450 to 700 °C resulted in the formation of pure inorganic HfO 2 fibers with diameters ranging from 0.1 to 0.8 μm depending on the concentration of HfO 2 −acetate nanoparticles in the spinning dope. Fourier transform infrared spectroscopy and Raman spectroscopy techniques were used to investigate the crystal structures of the HfO 2 fibers, which were confirmed by X-ray diffraction (XRD) results. XRD results showed the presence of both monoclinic and tetragonal crystal structures in the HfO 2 fibers. The type and size of the crystals formed depended on the concentration of HfO 2 −acetate nanoparticles in the initial spinning dope and on the calcination temperature. In particular, the formation of stable tetragonal crystal structures in the as-spun hybrid fibers with lower concentration of HfO 2 was achieved at lower temperature than the monoclinic-to-tetragonal transition temperature.