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Structural and morphological control is an effective approach for improvement of electrochemical properties in rechargeable batteries. One-dimensionally assembled structure composed of NASICON-type Na3 V2 (PO4 )3 nanoparticles were fabricated through an electrospinning method to meet the requirements for the development of efficient electrode materials in Na-ion batteries. High-temperature treatment of electrospun precursor fibers under an argon flow provides a nonwoven fabric of nanowires comprising crystallographically oriented nanoparticles of NASICON-type Na3 V2 (PO4 )3 within a carbon sheath. The mesostructure comprising NASICON-type Na3 V2 (PO4 )3 and carbon give a short sodium-ion transport pass and an efficient electron conduction pass. Electrochemical properties of NASICON-type Na3 V2 (PO4 )3 are improved on the basis of one-dimensional nanostructures designed in the present study.

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We investigate the electron transfer from a dissociatively adsorbed H 2 molecule to a Au(111) surface using the first-principles methods. A fractional electron transfers from a molecule to a substrate, and potential energy increases during the process. The initial energy increase coincides with that of the isolated, separated, and positively charged H 2 molecule calculated by the real-space density functional method. The barrier formation is due to the destabilization of the molecule induced by the electron transfer. The electronegativity difference between the adsorbate and the substrate determines the direction of the electron transfer.

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A novel aerobic manganese-catalyzed oxophosphorylation reaction of carbon-carbon double bonds of styrene derivatives and vinyl ethers using diethyl H-phosphonates was developed. This direct transformation of alkenes to β-ketophosphonate readily proceeded at room temperature via the direct incorporation of molecular oxygen present in air (open flask).

Introduction Development of Na-ion batteries is desired as alternative energy storage devices to Li-ion batteries. NASICON frameworks (Na3M2(XO4)3; X = Si4+, P5+, S6+, Mo6+, As5+) are suitable to Na-ion intercalation electrode materials due to pass for fast ion transport. In particular, Na3V2(PO4)3 is a promising candidate for cathode materials in Na-ion batteries, because Na3V2(PO4)3 exhibits relatively high redox potential of V3+/V4+ at 3.37 V (vs. Na/Na+) and moderate theoretical capacity of 117.6 mAh/g. However, low electronic conductivity and lattice volume change during sodiation/desodiation of Na3V2(PO4)3give rise to low performance about micrometer-scale particles that are often yielded through traditional solid-state reaction. Structural and morphological control can improve electrochemical properties of electrode materials. In the present study, we have designed mesostructure that consists of oriented Na3V2(PO4)3 nanoparticles in a carbon sheath, so as to meet the requirements as high-performance Na-ion electrode materials. The assembly comprising oriented nanoparticles possesses a short Na-ion transport pass and effectively relieves the elastic strain during sodiation/desodiation. In addition, the carbon sheath surrounding nanoparticles supplies a sufficient electron conductive pass. These features enable the long cycle performance and high rate capability of the electrode. Experimental Section The typical procedure for preparation of Na3V2(PO4)3 nanowire with the mesostructure from electrospun precursor fiber is as follows: 0.15 mol·dm−3 NH4VO3 and stoichiometric amount of NH4H2PO4 and NaOH were added to 10 ml of citric acid aqueous solution (0.12 mol·dm−3). To dissolve the reagents, the aqueous solution was aged for 1 h at 90 ºC. After cooling at room temperature, 60 g·dm−3poly(acrylic acid) was dissolved into the solution. Precursor fiber obtained by electrospinning was heated at 800 ºC for 10 h in Ar flow condition. The resultant materials were observed with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). For crystal structural analysis, X-ray diffraction was measured with Cu Ka radiation in steps of 0.01° over the range from 10 to 80º. Thermogravimetric analysis was conducted up to 1000 °C in air flow condition. Raman spectroscopy was recorded to confirm existence of amorphous carbon. Electrochemical properties were measured in three electrode beaker cells. The resultant nanowire including amorphous carbon (85 wt%) were ground with further acetylene black (10 wt%) and polytetrafloroethylene (5 wt%) into a paste for electrochemical measurements. Sodium metal pressed on a SUS-304 mesh was used for counter and reference electrodes. 1M NaClO4propylene carbonate solution was used as electrolyte. The cutoff voltages were 3.8 V for charging (Na-ion extraction) and 2.5 V for discharging (Na-ion insertion). Specific current rate and capacity were calculated for only active materials. Results and Discussion Obtained compounds were confirmed with powder X-ray diffraction (XRD) measurement and the Rietveld refinement. The XRD pattern was refined by Na3V2(PO4)3. Morphology of the product was observed with scanning electron microscopy (SEM). Precursor fiber exhibited fibrous morphology, estimated to be 500 nm in diameter with SEM. Even after the heating treatment, nowoven fabric consisting of nanowires was observed, though the diameter is reduced to 200 nm. To confirm the formation of the mesostructure, transmission electron microscopy (TEM) obeservation was carried out. Figure 1a shows core-sheath structure in nanowires, where amorphous carbon sheath that is around 50 nm in thickness enfolds with aggregated nanoparticles 20-50 nm in size. Indeed, the Raman spectrum of the nanowires showed the broaden G-band and D-band of amorphous carbon around 1580 cm-1 and 1350 cm-1. The thermogravimetric curve of nanowire measured in air flow condition also suggested the existence of the carbon sheath, the amount of which in the product was estimated to be around 12 wt%. Selected-area electron diffraction (SAED) analysis of the nanowire shows an arched pattern, suggesting that nanoparticles in the carbon sheath are crystallographically oriented into the carbon sheath (Figure 1b). The electrochemical properties of the nanowire were evaluated by the charge-discharge experiments at various current rate (0.1, 0.2, 0.5, 1 and 2C rate). The charge-discharge curves show the flat plateau potential of the redox V4+/V3+ couple at 3.37 V vs. Na/Na+, which is in good agreement with previous studies. The core-sheath nanowire shows an initial discharge capacity of 109 mAh/g at 0.1 C rate (theoretically 117.6 mAh/g) (Figure 2) and the initial discharge capacity at 1C rate is 94 mAh/g (80% of the theoretical capacity). Comparing with electrochemical properties of bulk Na3V2(PO4)3 that were obtained by solid-state reaction, The core-sheath nanowire exhibited lager capacity. The designed structure enabled efficient charge-discharge reaction at moderate current rate.

IntroductionThe chromium dioxide (CrO_2) is a half metallic ferromagnet which has both the metallic and semiconductive spin bands [1,2,3]. This material has been intensively investigated, because these half metallic spin bands induce the applications such as an enormously sensitive magnetic sensor and a MRAM etc. It was recently reported that the tunneling magnetoresistance (TMR) measurements in CrO_2/I/Co junctions showed the inverse TMR effects with the values of the TMR ratio of -24% and -1% at 5K and the room temperature, respectively by J. S. Parker et. al. [4]. The recent band calculations[5] support this inverse TMR effects, although the negative sign of the TMR is probably due to the insulator and/or Co. However, these values of the ratio are too small compared with the values expected theoretically in the junction using the half metal. The roughness of the interface between both layers probably reduces the values of the TMR ratio. The TMR effects have been measured using the soft ferromagnet coated cantilever for the conductive atomic force microscope (AFM) to prevent the TMR ratio from reducing owing to the roughness of the interface and effects of the insulator. This report shows the experimental results of the TMR at the room temperature in the single CrO_2 films deposited on single TiO_2 substrate using the conductive AFM method. ExperimentThe CrO_2 film was deposited by the CVD method[6] on the (110) single TiO_2 substrate. The thickness of the CrO_2 film was about 0.8µm. The TMR was measured keeping the constant distance of 2.0 nm between the CrO_2 film and the top of the cantilever for the conductive AFM at the room temperature in the vacuum level of about 1×10^-7 torr in the magnetic field between about -300 [Oe] and about 300 [Oe]. The magnetic field was applied toward the direction of c axis. The cantilever was coated by the soft ferromagnet of Ni_80Fe_20 with the thickness of about 300Å. The bias of 1mV was applied between CrO_2 film and the cantilever in the TMR measurements. The magnetization of CrO_2 film was measured to investigate the magnetic properties such as the coercive force H_c using VSM. 3. Results and discussion Fig. 1 shows the experimental results of the tunneling current between CrO_2 film and Ni_80Fe_20 film on the AFM cantilever at the room temperature in the vacuum using the bias of 1mV. The giant tunneling current flowed in the range of the magnetic field under the antiparallel magnetization state between the upper electrode and the lower one, which is in agreement with the behavior expected in the inverse type of the half metal. It was estimated that the coercive force Hc of CrO_2 was about 130 [Oe] from the results of the magnetization. The value was almost same