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1.
Lithium insertion in αI-VOPO4 and αII-VOPO4, either by chemical or electrochemical route, leads to the same new compound: αI-LiVOPO4 (space group P4/nmm). The structure, resolved by neutron and synchrotron diffraction, is made up of planes of corner-connected PO4 and VO5 polyhedra, whereas lithium atoms are located between the layers. The reversal of the short vanadyl bond that corresponds to the insertion-induced αII-αI transition finds an explanation in terms of lattice energy. It favors the migration of lithium ions in the (0 0 1) interlayer planes, a key parameter for the electrochemical performance as electrode material in Li-ion batteries. 相似文献
2.
Renée L. Beyer Hakan Kandemir Mohan Bhadbhade Ibrahim F. Sengul Chao-wei Leu Daniel Wenholz Naresh Kumar David StC. Black 《Tetrahedron letters》2018,59(51):4483-4486
Acylation reactions of 4,6-dimethoxyindoles with glyoxyloyl chlorides were achieved by the use of graphite powder in 1,2-dichloroethane at reflux. The products were monoketones as a result of decarbonylation, rather than the expected 1,2-diketones. Treatment of these monoketones with base led to their cyclisation and elimination of methanol to afford the novel dipyrrolo[2.3-a:1′,2′,3′-fg]acridin-12(1H)-ones. 相似文献
3.
A.Yu. Suntsov I.A. Leonidov M.V. Patrakeev V.L. Kozhevnikov 《Journal of solid state chemistry》2011,184(8):1951-1955
The oxygen content, conductivity and thermopower in the double perovskite-like cobaltite PrBaCo2O5+δ are reported in the oxygen partial pressure range 2×10−6-0.21 atm and temperatures between 650 and 950 °C. The electrical properties are shown to be continuous through the transition from δ>0.5 to δ<0.5. The variations of transport parameters with temperature and oxygen content reveal hole polaron hopping conduction within oxygen non-stoichiometry domain δ<0.5. 相似文献
4.
Clear evidence (in the form of structured diffuse scattering) is found for short range ordering of metal ions and associated induced structural relaxation in two members of the cubic BZN pyrochlore (Bi1.5−αZn0.5−β)(Zn0.5−γNb1.5−δ)O(7−1.5α−β−γ−2.5δ) solid solution. An average neutron powder diffraction structure refinement is carried out for one of these. Electron probe micro-analysis suggests that the primary mechanism for non-stoichiometry in cubic BZN is the removal of ZnO from the nominally fully occupied (Bi1.5Zn0.5)(Zn0.5Nb1.5)O7 end-member. A detailed bond valence sum analysis of a recently reported average crystal structure is used to suggest possible local cation ordering schemes along with the induced displacive relaxation that is likely to accompany such local cation ordering. The observed diffuse distribution is qualitatively interpreted via Monte Carlo modelling. 相似文献
5.
Kazuhiro Mori Ryoji Kiyanagi Kenji Iwase Takashi Sato Masaaki Sugiyama Toshiharu Fukunaga 《Journal of solid state chemistry》2006,179(11):3286-3294
In order to study the crystal structure of β‐Ca2SiO4, time-of-flight neutron powder diffraction experiments were carried out at temperatures between room temperature (RT) and 600 °C. Rietveld refinement at RT has shown that β‐Ca2SiO4 is monoclinic based on P21/n symmetry and two different types of Ca sites, Ca(1) and Ca(2). All interatomic distances within 3 Å were calculated, with the valences of Ca(1) with seven CaO bonds and Ca(2) with eight were estimated to be 1.87+ and 2+ by the Zachariasen-Brown-Altermatt formula (bond valence sum). Applying charge neutrality the two charge states of Ca in β‐Ca2SiO4 are [Ca(1)SiO4]2− and Ca(2)2+, respectively. Furthermore, the [Ca(1)SiO4]2− unit has the shortest Ca-O distance, and its length kept constant at 2.23 Å at all temperatures. In the short-range structure analysis at RT, the shortest Ca-O bond was also observed in a radial distribution function. These results imply that the [Ca(1)SiO4]2− unit has covalency on the shortest Ca-O in addition to Si-O. 相似文献
6.
D. Ramarajan 《Journal of solid state chemistry》2011,184(3):597-600
Cubic and chain-like structure of α-Mn2O3 with a high surface area was prepared by air oxidation of manganese chloride through sol process by adding hexamine and mercaptosuccinic acid as wetting agent, respectively. The as-synthesized products were characterized with X-ray powder diffraction (XRD), Energy Dispersive X-ray spectroscopy (EDX), transmission electron microscope (TEM), and selected area electron diffraction (SAED). The possible formation mechanism of α-Mn2O3 cubic and chain-like nanostructures has been proposed and discussed. 相似文献
7.
To determine the diffusion of untrapped carriers in β-rhombohedral boron, we constructed a feedback pico-ammeter based on pulse integration technique. This enabled measuring deviations from the bias in a 109 Ω sample in the order of 1 nA with 0.7 ms time resolution. For the first time, we obtained the drift velocity of optically generated untrapped electron-hole pairs 106(20) cm s−1 yielding for the band-determined diffusion coefficient and for the carrier mobility . Fitting Fick's second law to the measured trap-determined dispersion of carriers yields the ambipolar diffusion coefficient D*=0.043(14) and 0.28(10) cm2 s−1 at 260 and 340 K, respectively. The thermal activation energy of 0.18 eV agrees with the well-known trapping levels in β-rhombohedral boron. 相似文献
8.
Lakshmi V.R. Babu Syamala Tushar M. Khopade Prakash K. Warghude Ramakrishna G. Bhat 《Tetrahedron letters》2019,60(1):88-91
A dual cooperative organocatalytic approach for the synthesis of α, β-unsaturated ketones is described. This one pot transformation is realized via a domino Knoevenagel-Michael-retro Michael reaction sequence. Various aliphatic ketones reacted smoothly with aromatic as well as aliphatic aldehydes in presence catalytic amount of Meldrum’s acid and bifunctional amine. The highlights of this protocol are the easy availability of catalysts, high selectivity, and functional group tolerance. The reaction proved to highly E-selective with no side products emanating from self-condensation, unlike the base-mediated reactions. 相似文献
9.
Lithium ferrite, a mixed-inverse spinel of type AxBy[A1−xB1−y]O4 was produced through solid state synthesis by calcining a Li2CO3/Fe2O3 mixture at 900 °C. The presence of both the ordered α-phase and disordered β-phase of LiFe5O8 was confirmed by XRD analysis, while formation of the latter was achieved by air quenching from high temperature. Laser Raman analysis was performed on both the α-LiFe5O8 and β-LiFe5O8 powders in order to achieve a reference set of Raman shifts for the spinel. The strongest, characteristic Raman peaks were determined to be 493, 382, 358, 300, and 263 cm−1 for both phases while smaller peaks at 202 and 236 cm−1 present in the α-phase were diminishing in intensity when the β-phase was present, thus providing unique identifiers for the presence of the disordered ferrite structure. SEM images taken of the synthesized LiFe5O8 powders showed particle sizes of less than 300 nm and an even particle size distribution. 相似文献
10.
The electrical conductivity of γ′-Bi2MoO6 was surveyed between 450 and 750 °C as a function of oxygen partial pressure, in the range 0.01-1 atm. A − power law dependence, consistent with a Frenkel defect model of doubly ionized oxygen vacancies and interstitials, is evidence for an n-type semiconductive component, with an optical band gap of 2.9 eV. The absence of this dependence is used to map the onset of dominant ionic conduction. 相似文献
11.
Y.H. YuanX.N. Ying 《Solid State Sciences》2012,14(1):84-88
Double perovskite YBaCuFeO5+δ samples were prepared by two different sintering procedures. The interstitial oxygen contents of two samples are different which were estimated from thermogravimetric analysis (TGA). The mechanical spectrum below room temperature was measured using the vibrating reed method at kilohertz frequencies. Two internal friction peaks can be discerned in two samples above 200 K whose intensities show a correlation with the interstitial oxygen concentration. The lower temperature peak is attributed to the freezing transition of the interstitial oxygen. Another internal friction peak observed around 150 K can be explained by the stress induced hopping of electrons in the Fe ion sites. 相似文献
12.
Xukai Guan Dong An Guofeng Liu Heng Zhang Jigang Gao Tianyun Zhou Guangliang Zhang Suoqin Zhang 《Tetrahedron letters》2018,59(25):2418-2421
Chiral imidodiphosphoric acids were employed as catalysts for the enantioselective α-chlorination of β-keto esters and amides using NCS as the chlorine source, providing a series of optically active products with good to high enantioselectivities (74–95% ee) and excellent yields (92–99%). This represents the first report of the Brønsted acid catalyzed enantioselective α-chlorination of cyclic β-keto derivatives. 相似文献
13.
Keikichi Nakamura 《Journal of solid state chemistry》2003,173(2):299-308
The effects of oxygen reduction treatments on the magnetic properties of La-deficient manganites, La1−ΔMnO3+δ and Sr- and Ca-doped manganites, La1−xMxMnO3+δ (M: Sr, Ca) have been investigated to confirm the contrasting oxygen reduction effects on the magnetization properties. It is found that oxygen reduction treatments in reduced oxygen pressures of 103- for La1−ΔMnO3+δ result in a continuous change in the magnetization but the reduction treatments for La1−xMxMnO3+δ result in a negligible change under the same reduction conditions. To interpret the contrasting behavior of the La-deficient manganites, several possible models have been discussed. Among the models, the most probable model is that vacancies generated by the La deficiency Δ are partially replaced by Δ2(=Δ−Δ1?Δ1) Mn ions to give both La and Mn site vacancies according to the formula La1−ΔVΔMnO3+δ→{La1−ΔMnΔ2VΔ1}{Mn1−Δ2VΔ2}O3+δ. Details of thermodynamic basis of this model have been presented. 相似文献
14.
Steffen Falgner 《Journal of organometallic chemistry》2010,695(24):2614-2617
An efficient, convenient, and reliable multi-step synthesis of rac-2′-(trimethylsilyl)isovaline (rac-3) that uses inexpensive reagents in all steps has been developed, starting from diethyl malonate (overall yield 28%). Compound rac-3 is the first α-ethylated α,α-dialkylated silicon-containing α-amino acid. 相似文献
15.
Xiang-Zhu WangZhu-Jun Yao Hongpeng LiuManchao Zhang Dajun YangClifford George Terrence R Burke Jr. 《Tetrahedron》2003,59(32):6087-6093
Src homology 2 (SH2) domains provide connectivity in protein-tyrosine kinase (PTK)-dependent signaling through their high affinity association with phosphotyrosyl (pTyr)-containing peptide sequences. Because recognition of pTyr residues is central to SH2 domain-binding affinity, design of pTyr-mimicking residues has been one component of SH2 domain signaling antagonist development. Reported herein is the synthesis of (±)-(rel-1R,2R,5S)-3-acetyl-1,2,3,4,5,6-hexahydro-8-O-phosphoryl-1,5-methano-3-benzazocine-2-carboxylic acid methyl ester (3c) as a monomeric pTyr-mimicking analogue that constrains three torsion angles (χ1=168°; χ2=−85°; φ1=−113°) to values approximating those observed for a pTyr residue bound to the Grb2 SH2 domain (χ1=182°; χ2=−89°; φ1=−132°). Compound 3c differs from our previously reported analogue, (±)-(rel-1R,2R,5S)-3-acetyl-1,2,3,4,5,6-hexahydro-1-methyl-1,5-methano-3-benzazocin-8-ol, in lacking a methyl substituent at the bridgehead 1-position. Molecular modeling studies had indicated that this methyl group could potentially hinder SH2 domain binding. Synthesis of the desmethyl derivative was achieved by formation of the methanobenzazocine ring system using an intramolecular electrophilic cyclization that proceeds through an activated acyliminium intermediate. Importantly, the correct relative (2R) stereochemistry at the ‘α-carboxyl’-bearing carbon is obtained through base-catalyzed equilibration of a (2S/2R) diastereomeric mixture that results from intramolecular ring closure. Comparison of Grb2 SH2 domain-binding affinity of 3c (IC50=1167 μM) with conformationally flexible phosphorylated (±)-N-acetyl-tyrosine methyl ester (15; IC50=1469 μM) revealed no apparent enhancement in affinity. This apparent ineffectiveness of ‘local conformational constraint’ on SH2 domain-binding affinity of the monomeric pTyr mimetic is consistent with previous reports obtained by conformationally constraining pTyr-mimicking residues that were contained within peptide platforms. Although not providing high binding affinity in its current form, the novel 1,5-methano-3-benzazocine ring system may afford a novel platform for further elaboration and development of small molecule SH2 domain signaling antagonists. 相似文献
16.
The structure of the low-temperature form of β-La2WO6 has been determined from laboratory X-ray, neutron time-of-flight and electron diffraction data. This tungstate crystallizes in the non-centrosymmetric orthorhombic space group (no. 19) P212121, with Z=8, a=7.5196(1) Å, b=10.3476(1) Å, c=12.7944(2) Å, and a measured density 7.37(1) g cm−3. The structure consists of tungsten [WO6] octahedra and tetrahedral [OLa4]. Tungsten polyhedra are connected such that [W2O11]10− units are formed. 相似文献
17.
The structure of α-CsB9O14 was re-examined because the first determination corresponded to a poor reliability factor (12.9%). Single crystals were obtained by heating, melting and slow cooling a stoichiometric mixture (1:4) of β-Cs[B5O6(OH)4]·2H2O and H3BO3. This compound crystallizes in the non-centrosymmetric orthorhombic space group P2221 (and not P4122) with the following parameters: a=8.732(2)Å, b=8.767(3)Å, c=15.736(4)Å, V=1204.6(6)Å3, Z=4; after taking into consideration twinning, the structure was refined from 3188 reflections until R1=0.0304. It consists of two infinite, interleaved three-dimensional boron-oxygen frameworks of the Fundamental Building Blocks formed by two B3O6 and one B3O7 groups; its shorthand notation is 9:∞3[(3:2Δ+T)+2(3:3Δ)] (Δ, triangle BO3 and T, tetrahedron BO4). Knowledge of the correct space group and the structure of α-CsB9O14 may help in the study of its physical properties, especially the non-linear optical ones. 相似文献
18.
A. Malak-Polaczyk C. Matei-Ghimbeu E. Frackowiak 《Journal of solid state chemistry》2010,183(4):969-828
In the present work a composite of carbon with λ-MnO2 have been synthesized by a simple two-step route. In the first step, to obtain LiMn2O4/carbon material, mesoporous activated carbon was impregnated with the solution of precursor metal salts and heated subsequently. As-prepared materials were acid treated which resulted in the formation of λ-MnO2/carbon. Physical properties, structure and specific surface area of electrode materials were studied by TEM, X-ray diffraction and nitrogen sorption measurements. Voltammetry cycling, galvanostatic charge/discharge and impedance spectroscopy measurements performed in two- and three-electrode cells have been applied in order to measure electrochemical parameters. TEM images confirmed well dispersed λ-MnO2 particles on the surface of carbon material. The carbon in the composite plays an important role as the surface area enhancing component and a support of pseudocapacitive material. Furthermore, the through-connected porosity serves as a continuous pathway for electrolyte transport. A synergetic effect of the porous carbon framework and of the redox properties of the λ-MnO2 is at the origin of improvement of specific capacitance values which has been observed for composites after delithiation. 相似文献
19.
Y. Mugnier C. GalezJ.M. Crettez P. BoursonC. Opagiste J. Bouillot 《Journal of solid state chemistry》2002,168(1):76-84
The lithium iodate ionic conduction in the polar c-axis direction is studied between 35 and 470 K for crystals grown in various conditions. So far, to separate processes induced by the nature of electrodes, the impedance spectroscopy technique had been used at room temperature with both metallic and ideally polarizable insulating electrodes, so that a relaxation of space charges was clearly identified. Here, the temperature dependence of the hopping ionic conductivity exhibits quite different activation energies well related to the growth conditions. Following low-temperature Raman and thermodynamic experiments, a new approach based on a vacancy diffusion mechanism is proposed. Experimental conductivity results are then correlated with the valence, size and concentration of extrinsic impurities incorporated during the growth and analyzed by plasma spectroscopy. Finally, a discussion is made on still not well-understood phenomena such as the strong increase of photorefractivity or the enhancement of some Bragg reflections. 相似文献
20.
Jakoah Brgoch Ruslan Prozorov Gordon J. Miller 《Journal of solid state chemistry》2010,183(12):2917-2924
Polycrystalline samples of two complex intermetallic borides Zr2Fe1−δRu5+δB2 and Zr2Fe1−δ(Ru1−xRhx)5+δB2 (δ=ca. 0.10; x=0.20) were synthesized by high-temperature methods and characterized by single-crystal X-ray diffraction, energy dispersive spectroscopy, and magnetization measurements. Both structures are variants of Sc2Fe(Ru1−xRhx)5B2 and crystallize in the space group P4/mbm (no. 127) with the Ti3Co5B2-type structure. These structures contain single-atom, Fe-rich Fe/Ru or Fe/Ru/Rh chains along the c-axis with an interatomic metal-metal distance of 3.078(1) Å, a feature which makes them viable for possible low-dimensional temperature-dependent magnetic behavior. Magnetization measurements indicated weak ferrimagnetic ordering with ordering temperatures ca. 230 K for both specimens. Tight-binding electronic structure calculations on a model “Zr2FeRu5B2” using LDA yielded a narrow peak at the Fermi level assigned to Fe-Fe antibonding interactions along the c-axis, a result that indicates an electronic instability toward ferromagnetic coupling along these chains. Spin-polarized calculations of various magnetic models were examined to identify possible magnetic ordering within and between the single-atom, Fe-rich chains. 相似文献