Articles you may be interested inEvolution of structure, dielectric properties, and re-entrant relaxor behavior in Ba5LaxSm1−xTi3Nb7O30 (x = 0.1, 0.25, 0.5) tungsten bronze ceramics

A 12R-type hexagonal perovskite, Ba(Ti 1/2 Mn 1/2 )O 3 , has been prepared by a mixed oxide route at 1250 °C in air and the crystal structure established by a joint Rietveld refinement of powder X-ray and neutron diffraction data at room temperature [space group R3 hm, a ) 5.69135(2) Å, and c ) 27.91860( 15) Å]. The structure consists of a (hhcc) 3 stacking sequence of BaO 3 close-packed layers along the c-axis with face sharing M 3 O 12 trimers connected by a vertex sharing octahedron. Partial ordering of the Ti +IV and Mn +IV ions occurs in the B-site substructure; Mn +IV ions occupy the central octahedral site in the trimers, Ti +IV ions occupy the octahedral site in the vertex sharing octahedron, and both ions occupy the outer octahedral site of the trimers. Impedance spectroscopy and microwave dielectric resonance measurements on dense pellets (>97% of the theoretical X-ray density) show the title compound to be a modest dielectric insulator at room temperature with high permittivity, r ∼ 45 (at both radio and microwave frequencies); a modest unloaded quality factor, Q u ∼ 2026 (at ∼5.75 GHz); and a temperature coefficient of resonant frequency, TC f ) -4 ppm K -1 .

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Aerosol-assisted chemical vapor deposition (AACVD) was used for the first time in the preparation of thin-film electrochromic nickel(II) oxide (NiO). The as-deposited films were cubic NiO, with an octahedral-like grain structure, and an optical band gap that decreased from 3.61 to 3.48 eV on increase in film thickness (in the range 500–1000 nm). On oxidative voltammetric cycling in aqueous KOH (0.1 mol dm–3) electrolyte, the morphology gradually changed to an open porous NiO structure. The electrochromic properties of the films were investigated as a function of film thickness, following 50, 100, and 500 conditioning oxidative voltammetric cycles in aqueous KOH (0.1 mol dm–3). Light modulation of the films increased with the number of conditioning cycles. The maximum coloration efficiency (CE) for the NiO (transmissive light green, the “bleached” state) to NiOOH (deep brown, the colored state) electrochromic process was found to be 56.3 cm2 C–1 (at 450 nm) for films prepared by AACVD for 15 min followed by 100 “bleached”-to-colored conditioning oxidative voltammetric cycles. Electrochromic response times were <10 s and generally longer for the coloration than the bleaching process. The films showed good stability when tested for up to 10 000 color/bleach cycles. Using the CIE (Commission Internationale de l’Eclairage) system of colorimetry the color stimuli of the electrochromic NiO films and the changes that take place on reversibly oxidatively switching to the NiOOH form were calculated from in situ visible spectra recorded under electrochemical control. Reversible changes in the hue and saturation occur on oxidation of the NiO (transmissive light green) form to the NiOOH (deep brown) form, as shown by the track of the CIE 1931 xy chromaticity coordinates. As the NiO film is oxidized, a sharp decrease in luminance was observed. CIELAB L*a*b* coordinates were also used to quantify the electrochromic color states. A combination of a low L* and positive a* and b* values quantified the perceived deep brown colored state.

27Keywords: Li-S battery, high volumetric capacity, monodisperse, interconnected carbon 28 nanospheres, close-packed 29 30We report a Li-S battery cathode of high volumetric-capacity enabled by novel micro-and meso-31 structuring. The cathode is based on monodisperse highly porous carbon nanospheres derived from 32 a facile template-and surfactant-free method. At the mesoscale, the nanospheres structure into 33 interconnected close-packed clusters of a few microns in extent, thus facilitating the fabrication of 34 dense crack-free high areal sulfur loading (5 mg cm -2 ) cathodes with high electrical conductivity 35 and low cathode impedance. A combination of the nitrogen doping (5 wt%), high porosity (2.3 cm 3 36 g -1 ) and surface area (2900 m 2 g -1 ) at the microscale enables high sulfur immobilization and 37 utilization. The cathode delivers amongst the best reported volumetric capacity to date, above 38 typical Li-ion areal capacity at 0.2C over 200 cycles and low capacity fading of 0.1% per cycle at 39 0.5C over 500 cycles. The compact cathode structure also ensures a low electrolyte requirement (6 40 µL mg -1 ), which aids a low overall cell weight, and further, amongst the best gravimetric capacities 41 published to date as well. 42

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