ABSTRACT
Graphene oxide (GO)-the oxidized form of graphene-is actively studied in various fields, such as energy, electronic devices, separation of water, materials engineering, and medical technologies, owing to its fascinating physicochemical properties. One major drawback of GO is its instability, which leads to the difficulties in product management. A physicochemical understanding of the ever-changing nature of GO can remove the barrier for its growing applications. Here, we evidencde the presence of intrinsic, metastable and transient GO states upon ripening. The three GO states are identified using a [Formula: see text] transition peak of ultraviolet-visible absorption spectra and exhibit inherent magnetic and electrical properties. The presence of three states of GO is supported by the compositional changes of oxygen functional groups detected via X-ray photoelectron spectroscopy and structural information from X-ray diffraction analysis and transmission electron microscopy. Although intrinsic GO having a [Formula: see text] transition at 230.5 ± 0.5 nm is stable only for 5 days at 298 K, the intrinsic state can be stabilized by either storing GO dispersions below 255 K or by adding ammonium peroxydisulfate.
ABSTRACT
Fabricating large, high-crystalline-quality single-crystal samples of hexagonal ferrite Ba(Fe1-x Sc x )12O19 is the first important step to elucidating its helimagnetic structure and developing it for further applications. In this study, single crystals of Ba(Fe1-x Sc x )12O19 of various Sc concentrations x were successfully grown by the spontaneous crystallization method using Na2O-Fe2O3 flux. We determined the optimal starting composition of reagents for Ba(Fe1-x Sc x )12O19 growth as a function of x. In situ monitoring of the crystal nucleus generation accelerated the success of crystal growth. The obtained crystals comprised black and lamellate structures with a size of 13 mm × 8 mm × 2 mm and a surface of {001} orientation. X-ray diffraction and elemental analysis revealed that the obtained crystals were composed of single-phase Ba(Fe1-x Sc x )12O19 of high crystalline quality. The lattice constants a and c increased linearly with increasing x, thereby following Vegard's law. The temperature dependence of magnetization and the magnetization curves at 77 K of the x = 0.128 crystal exhibited behavior characteristics of helimagnetism. Neutron diffraction measurements of the x = 0.128 crystal exhibited magnetic satellite reflection peaks below 211 K, providing evidence that Ba(Fe1-x Sc x )12O19 behaves as a helimagnetic material.
