408 research outputs found
Versatile electrochemical cell for Li/Na-ion batteries and high-throughput setup for combined operando X-ray diffraction and absorption spectroscopy
A fully operational setup (electrochemical cells, sample changer and interfacing software) that enables combined quasi-simultaneous operando X-ray diffraction (XRD) and absorption (XANES and EXAFS) measurements coupled with electrochemical characterization has been realized for synchrotron based studies. Combined XRD, XANES and EXAFS analysis provides a deep insight into the working mechanisms of electrode materials
Water‐Stable DMASnBr3 Lead‐Free Perovskite for Effective Solar‐Driven Photocatalysis
Water-stable metal halide perovskites could foster tremendous progresses in several research fields where their superior optical properties can make differences. In this work we report clear evidence of water stability in a lead-free metal halide perovskite, namely DMASnBr3, obtained by means of diffraction, optical and x-ray photoelectron spectroscopy. Such unprecedented water-stability has been applied to promote photocatalysis in aqueous medium, in particular by devising a novel composite material by coupling DMASnBr3 to g-C3N4, taking advantage from the combination of their optimal photophysical properties. The prepared composites provide an impressive hydrogen evolution rate >1700 μmol g-1 h-1 generated by the synergistic activity of the two composite costituents. DFT calculations provide insight into this enhancement deriving it from the favorable alignment of interfacial energy levels of DMASnBr3 and g-C3N4. The demonstration of an efficient photocatalytic activity for a composite based on lead-free metal halide perovskite in water paves the way to a new class of light-driven catalysts working in aqueous environments
A study of management's relationship with stockholders since the 1920's
Thesis (M.S.)--Boston UniversityIt was the purpose ot this study (1) to trace management's relationship with stockholders from the 1920's up to the present time, noting the change in management's attitude, policies, and practices and (2) to learn the reasons for this change
Solar silicon from directional solidification of MG silicon produced via the silicon carbide route
A process of metallurgical grade (MG) silicon production is presented which appears particularly suitable for photovoltaic (PV) applications. The MG silicon is prepared in a 240 KVA, three electrode submerged arc furnace, starting from high grade quartz and high purity silicon carbide. The silicon smelted from the arc furnace was shown to be sufficiently pure to be directionally solidified to 10 to 15 kg. After grinding and acid leaching, had a material yield larger than 90%. With a MG silicon feedstock containing 3 ppmw B, 290 ppmw Fe, 190 ppmw Ti, and 170 ppmw Al, blended with 50% of off grade electronic grade (EG) silicon to reconduct the boron content to a concentration acceptable for solar cell fabrication, the 99% of deep level impurities were concentrated in the last 5% of the ingot. Quite remarkably this material has OCV values higher tham 540 mV and no appreciable shorts due to SiC particles
In operando Synchrotron XRD/XAS Investigation of Sodium Insertion into the Prussian Blue Analogue Cathode Material Na 1.32 Mn[Fe(CN) 6 ] 0.83 · z H 2 O
Prussian Blue Analogues (PBAs) with general formula NaxMA[MB(CN)6]y·z H2O (MA, MB = transition metal) are promising low cost, high rate and high capacity cathodes for sodium ion battery (SIB) technology. Here, we have studied the PBA Na1.32Mn[Fe(CN)6]0.83·z H2O (z = 3.0 and 2.2) with varying structural modifications (monoclinic and cubic) using in operando quasi-simultaneous X-ray diffraction (XRD) and X-ray absorption spectroscopy (XAS). We observed a series of reversible structural phase transitions which accompany Na insertion/extraction during electrochemical cycling. The samples show pronounced differences in their galvanostatic charge and discharge profiles which could be linked to structural and electronic response. Different desodiation and sodiation mechanisms were identified. The influence of [Fe(CN)6] vacancies and water content on the electrochemical performance was investigated
Evidence of a structural anomaly at 14 K in polymerised CsC60
We report the results of a high-resolution synchrotron X-ray powder
diffraction study of polymerised CsC in the temperature range 4 to 40 K.
Its crystal structure is monoclinic (space group I2/m), isostructural with
RbC. Below 14 K, a spontaneous thermal contraction is observed along
both the polymer chain axis, and the interchain separation along [111],
. This structural anomaly could trigger the occurrence of the spin-singlet
ground state, observed by NMR at the same temperature.Comment: 8 pages, 5 figures, submitte
Improving In-Situ Sodium Metal Plating on Copper Foil Through Optimization of Mechanical Pressure: Towards High-Performance Anode-Free Sodium Ion Batteries
Herein we report key developments on the scale-up of sodium ion anode free batteries through investigation of the effects of applied external pressure cell performance. Sodium ion anode free puts extra emphasis on high plating and stripping efficiency of sodium metal at the anode surface, due to the lack of an excess of the transporting ion. We demonstrate excellent Na||Cu half-cell results in coin cell configuration, and the scalability of the anode-free concept is further demonstrated, by plating and stripping of sodium metal on copper foils 10-fold larger (>10 cm 2) than in other studies in coin cells (∼1 cm2). It is discovered that pressure is paramount in establishing dendrite free sodium deposition at this scale through investigating the half-cell cycling at 56–743 kPa. Achieving a low hysteresis in these large-area cells is found to only require moderate pressures (∼185 kPa). However, achieving a high cycle life required increasing the pressure to 743 kPa. It is only at these high pressures that non-dendritic sodium deposition is demonstrated due to a homogeneous plating distribution enabled by proper contact between electrodes, as confirmed by impedance measurements and optical imaging of the deposited sodium
Recovering Metallicity in A4C60: The Case of Monomeric Li4C60
The restoration of metallicity in the high-temperature, cubic phase of Li4C60
represents a remarkable feature for a member of the A4C60 family (A = alkali
metal), invariably found to be insulators. Structural and resonance technique
investigations on Li4C60 at T > 600 K, show that its fcc structure is
associated with a complete (4e) charge transfer to C60 and a sparsely populated
Fermi level. These findings not only emphasize the crucial role played by
lattice symmetry in fulleride transport properties, but also re-dimension the
role of Jahn-Teller effects in band structure determination. Moreover, they
suggest the present system as a potential precursor to a new class of
superconducting fullerides.Comment: 4 pages, 3 figure
Superconductivity in NdFe1-xCoxAsO (0.05 < x < 0.20) and rare-earth magnetic ordering in NdCoAsO
The phase diagram of NdFe1-xCoxAsO for low cobalt substitution consists of a
superconducting dome (0.05 < x < 0.20) with a maximum critical temperature of
16.5(2) K for x = 0.12. The x = 1 end member, NdCoAsO, is an itinerant
ferromagnet (TC = 85 K) with an ordered moment of 0.30(1) BM at 15 K. Below TN
= 9 K, Nd spin-ordering results in the antiferromagnetic coupling of the
existing ferromagnetic planes. Rietveld analysis reveals that the
electronically important two-fold tetrahedral angle increases from 111.4 to
115.9 deg. in this series. Underdoped samples with x = 0.046(2) and x =
0.065(2) show distortions to the orthorhombic Cmma structure at 72(2) and 64(2)
K, respectively. The temperature dependences of the critical fields Hc2(T) near
Tc are linear with almost identical slopes of 2.3(1) T K-1 for x = 0.065(2), x
= 0.118(2) and x = 0.172(2). The estimated critical field Hc2(0) and
correlation length for optimally doped samples are 26(1) T and 36(1) Angstrom.
A comparison of the maximum reported critical temperatures of
well-characterized cobalt doped 122- and 1111-type superconductors is
presented.Comment: accepted to PR
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