Interrelation between inhomogeneity and cyclability in O3‐NaFe1/2Co1/2O2

O3‐NaFe_1/2Co_1/2O₂ shows initial capacity of 160 mAh/g and an average operating voltage of 3.1 V (vs. Na) with good cyclability, and is a promising candidate of the cathode materials for sodium‐ion secondary batteries (SIBs). Here, we found that the cyclability of the slowly‐cooled sample is much worse than that of quenched one, even though the former sample keeps the O3‐type structure. The energy dispersive X‐ray spectroscopy (EDX) images suggest that the slow‐cooled sample (Na_x Fe_1–yCo_y O₂) is inhomogeneous in the Fe concentration (1 – y), perhaps triggered by the Na deficiency (1 – x). We ascribed the poor cyclability in the slowly‐cooled sample to the concentration inhomogeneity (Δy). The Δy is further responsible for the fluctuation of the lattice constants (a and c), as revealed by the Williamson–Hall plot. (© 2016 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

NO2 sensing properties of YSZ-based sensor using NiO and Cr-doped NiO sensing electrodes at high temperature

Nickel oxide and chromium-doped nickel oxide (Ni_0.95Cr_0.03O_1−δ ) were prepared by thermal decomposition of nitrates. The obtained NiO and Ni_0.95Cr_0.03O_1−δ samples were utilized as sensing electrodes (SEs) in yttria-stabilized zirconia (YSZ)-based sensors for detection of NO₂ at 800 °C under wet condition (5 vol.% H₂O). While the mixed-potential-type planar sensor attached with NiO-SE gave rather large NO₂ sensitivity, the sensor attached with Ni_0.95Cr_0.03O_1−δ -SE exhibited fast recovery rate with an acceptable sensitivity. The Δemf (electromotive force) of the sensors varied linearly with NO₂ concentration in the examined range of 50–400 ppm on a logarithmic scale. Based on the results of measurements for polarization, complex impedance and gas phase catalysis, the fast recovery was attributable to the high rate for the anodic reaction of O₂ at the Ni_0.95Cr_0.03O_1−δ /YSZ interface, and the lower NO₂ sensitivity was caused by both the high rate for the anodic reaction of O₂ and the high degree for the gas phase conversion of NO₂ to NO.     

Tomographic implementation of astronomical speckle imaging from bispectra

A bispectral method for astronomical speckle imaging utilizes an average speckle bispectrum of an object to derive its Fourier phase. There has been, however, a problem in conventional bispectral algorithm owing to difficulty in processing bispectral data in a four-dimensional (4D) space. In this paper, we propose an implementation to overcome this problem, where a one-dimensional (1D) object projection is reconstructed from a two-dimensional (2D) average bispectrum of speckle projections, and object projections so obtained at various angles are then tomographically combined into a 2D object image. In this tomographic approach, processes are separable into those for individual projection angles, implying that bispectral data required to be stored at a time are from 4D to 2D and computation time can be substantially reduced by parallelizing angle-by-angle processes. We have performed experiments using simulated and observed data, and have demonstrated the feasibility of the present approach with an achievable accuracy comparable to that of a conventional approach.     

Electron-active cyclotron resonance in p-doped InMnAs in high magnetic fields

We present a theoretical and experimental study of electron-active cyclotron resonance in p-doped InMnAs in high magnetic fields. Results are based on an 8-band Pidgeon–Brown model generalized to include finite k_z effects and s(p)–d exchange interaction between itinerant carriers and Mn d-electrons. The e-active transitions in the valence band in p-doped samples take place due to the nature of multiple valence bands (heavy and light holes). We have calculated the absorption spectra in high magnetic fields and identified optical transitions which contribute to the cyclotron resonance for both e-active and h-active polarizations. Calculations show agreement with experimental results.     

Observation of the fast potential change at L-H transition by a heavy-ion-beam probe on JFT-2M

The fast potential change near the separatrix is measured directly at the L-H transition by a heavy-ion-beam probe. The potential changes with two different time scales at the L-H transition triggered by a sawtooth crash: it drops at first with the time scale of 10--100 mus just after the arrival of the heat pulse due to the sawtooth crash. Then, it decreases again at a few 100 mus after the first drop at a time scale of about 200 mus.     

Modified Vonk's Method to Determine Crystallinity and Crystal Distortion in Polymers

Using a modified method developed from Vonk's method, detailed values of crystallinity and crystal disorder were obtained by wide angle X-ray diffraction (WAXD). In Vonk's method, the crystallinity (w) is determined by extrapolation of the WAXD experimental curve back to zero scattering angle, while the distortion factor (k) is determined by the inclination of the experimental curve at zero scattering angle. In our new method, both w and k are determined at the same time by using the least squares method. In order to show the efficiency of our method, the new fitting procedure was applied to the experimental values of polyethylene and polyethylene terephthalate as measured by Vonk, and the values of w and k determined by our new method were compared with those found by Vonk's method. The new fitting method has the advantage that it uses the whole experimental curve. Moreover, our modified Vonk's method enables us to discuss crystal distortions as arising from first-kind (thermal) disorder and second-kind (paracrystalline) disorder.     

Study of reduction processes over cerium oxide surfaces with atomic hydrogen using ultra accelerated quantum chemical molecular dynamics

Ceria plays an important role in catalysis, due to its ability to store and release oxygen depending on the condition present in the catalyst environment. To analyze the role of ceria in catalytic reactions, it is necessary to know the details of the interaction of ceria surface with environmentally sensitive molecules. This study was conducted using ultra accelerated quantum chemical molecular dynamics. Its purpose was to investigate the reduction process of the (1 1 1) and (1 1 0) surfaces of ceria with atomic hydrogen as well as water desorption mechanisms from the surfaces. This simulation demonstrated that when a high-energy colliding hydrogen atoms are adsorbed on the ceria, it pulls up an O atom from the ceria surfaces and results in the formation of a H₂O molecule. This is the first dynamics simulation related to such reduction processes based on quantum chemistry.