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1.
>为获得综合性能更好的锂离子二次电池正极材料, 分析了Co掺杂对Li xNiO 2电化学性能的影响. 采用密度泛函DFT理论对Li xNiO 2和Li xNi 0.5Co 0.5O 2的平均放电电压和态密度进行了计算. 同时, 用共沉淀法制备了Li xNiO 2和Li xNi 0.5Co 0.5O 2锂离子二次电池正极材料, 并对其进行了XRD结构分析和恒流充放电测试. 实验和计算结果表明: 随锂离子嵌入正极(电池放电), 电池的电压逐渐降低, 材料的态密度峰向低能量方向移动; 与Li xNiO 2相比, Li xNi 0.5Co 0.5O 2的电压平台相对较高(当0.25≤ x≤0.5), 而且在Li +嵌/脱时, Li xNi 0.5Co 0.5O 2的结构变化相对较小; Co离子的掺入, 减小了NiO 6八面体的畸变度, 使材料的电化学稳定性得以提高. 在钴掺杂镍酸锂体系中, NiO 6和CoO 6具有相互的稳定作用. 相似文献
2.
Densities have been measured for the electrolyte (NaCl, NaBr and NaI)‐monosaccharide (D ‐mannose and D‐ribose)‐water solutions at 298.15 K. These data have been used to calculate the apparent molar volumes of the saccharides ( VΦ,S) and electrolytes ( VΦ,E) in the studied solutions. Infinite dilution apparent molar volumes, VΦ,S0 and VΦ,E0, have been evaluated, together with the standard transfer volumes of the saccharides (Δ tVS0) from water to aqueous electrolyte solutions and those of the electrolytes (Δ tVE0) from water to aqueous saccharide solutions. It was shown that both the Δ tVS0 and Δ tVE0 values are positive and increase with increasing molalities of sodium halides and saccharides, respectively. Overall, the Δ tVS0 and Δ tVE0 values have the order of NaCl > NaBr > NaI except for NaI‐ribose and NaI‐ribose. Volumetric interaction parameters for the electrolyte‐monosaccharide pairs in water were obtained and interpreted by the stereochemistry of the monosaccharide molecules and the structural interaction model. 相似文献
3.
Biotransformations of the N-phthaloyl derivatives of d- and l-methionine and of d- and l-ethionine by Beauveria bassiana ATCC 7159 or Beauveria caledonica ATCC 64970 produce the corresponding ( SS) sulfoxides in good yield and diastereomeric excess. Pure ( SSSC) diastereomers can be obtained from l-series substrates by crystallisation of the biotransformation extract, and the corresponding ( SSRC) products obtained from d-series substrates by chromatography of the biotransformation extract. Hydrogen peroxide-catalysed oxidation of the N-phthaloyl derivatives of d- and l-methionine and of d- and l-ethionine gives diastereomeric mixtures from which the ( SSSC) and ( RSRC) diastereomers can be obtained by crystallisation, and the ( SSRC) and ( RSSC) diastereomers obtained by chromatography. N-Cbz- and N- t-Boc methionines are also converted to sulfoxides with predominant ( SS) configuration by both B. bassiana and B. caledonica, but the isolated yields and d.e. of products were generally lower than those obtained from the N-phthaloyl substrates.Removal of the N-phthaloyl group from diastereomerically pure methionine and ethionine sulfoxides gave the corresponding amino acid sulfoxides in high yield; removal of N-Cbz and N- t-Boc groups from protected methionine sulfoxides was also achieved without loss of configuration at sulfur. 相似文献
4.
New members of the AnBn−1O 3n perovskite-like family (Ba 5KNb 5O 18 and Sr 6Nb 4SnO 18 compounds) with n = 6 have been synthesized and studied by the X-ray powder diffraction. Their crystal structures were found to belong to the Ba 6Nb 4TiO 18-type with a = 0.57840(7) nm, c = 4.2532(5) nm and a = 0.5661(1) nm, c = 4.186(1) nm for Ba 5KNb 5O 18 and Sr 6Nb 4SnO 18, respectively. It was shown that Ba and K ( A-atoms) are completely disordered in the crystal structure of Ba 5KNb 5O 18 compound. But Nb and Sn atoms ( B-atoms) in the crystal structure of the Sr 6Nb 4SnO 18 compound are quite ordered with the preferred Sn +4 and Nb 5+ cations localization in the center of perovskite-like block and on the boundaries of these blocks, respectively. Temperature and frequency dependencies of the real components of electric conductivity σI and dielectric permeability ɛI; specific electric conductivity at the direct current σdc have been obtained by the impedance spectroscopy method for Sr 6Nb 4SnO 18. 相似文献
5.
Ab initio energetic calculations based on the density functional theory (DFT) and projector augmented wave (PAW) pseudo-potentials method were performanced to determine the crystal structural parameters and phase transition data of the polymorphic rare-earth sesquioxides Ln2O 3 (where Ln=La-Lu, Y, and Sc) with A-type (hexagonal) and B-type (monoclinic) configurations at ground state. The calculated results agree well with the limited experimental data and the critically assessed results. A set of systematic and self-consistent crystal structural parameters, energies and pressures of the phase transition were established for the whole series of the A- and B-type rare-earth sesquioxides Ln2O 3. With the increase of the atomic number, the ionic radii of rare-earth elements Ln and the volumes of the sesquioxides Ln2O 3 reflect the so-called “lanthanide contraction”. With the increase of the Ln3+-cation radius, the bulk modulus of Ln2O 3 decreases and the polymorphic structures show a degenerative tendency. 相似文献
6.
In this study, the Schiff base ligands H 2L 1–H 2L 3 and their Cu II, Co II, Ni II, Fe III Ru III and VO IV complexes have been prepared and characterized by spectroscopic and analytical techniques. All the complexes are mononuclear.
Keto-enol tautomeric forms of the ligands have been investigated in polar and apolar solvents. The ligands favor the keto-form
in the C 7H 8 and C 6H 14. The C–C coupling reaction of the 2,6-di- t-butylphenol has been investigated by the Co II and Cu II complexes. Thermal properties of the complexes have been assessed using thermal techniques and similar properties were found.
In the Fe III and Ru III complexes, firstly, the coordinated water molecule is lost from the complex; in the second step, the chloride ion leaves
the molecule in the 300–350 °C temperature range. Finally, the complexes decompose to the appropriate metal oxide at the higher
temperature ranges. The electrochemical properties of the complexes have been studied in the two different solvents (DMF and
CH 3CN). 相似文献
7.
Binary As–Se glasses with different amounts of As content have been prepared and scanned with different heating rates (3 ≤ ψ ≤ 48 K min−1) over temperatures ranging from 300 to 450 K. Both the glass transition temperature (Tgl) and the temperature peak of crystallization (Tpc) increase as a function of As and/or the ψ values. A good correlation between Tgl and Tpc has been investigated. The observed increase in Tgl and Tpc by increasing the ψ values or as a function of As is well discussed in accordance with Lasocka’s relationship and using the average coordination number Acn, the viscosity at glass transition μ(Tgl) and the overall mean bond energy E. The glass transition Egl and crystallization activation energies (Egl and Epc) were determined based on the changes in Tgl and Tpc values due to the heating rate (ψ). The increase in the values of Egl and Epc with increasing the As content is expected due to the increase in Tgl and Tpc values. The kinetic exponent n and the crystal dimensionality m have been determined. 相似文献
8.
The 25% niobium substituted crystalline titanosilicate with the composition Na 1.5Nb 0.5Ti 1.5O 3SiO 4·2H 2O (Nb-TS) was synthesized under hydrothermal conditions. Its selectivity for radioactive 137Cs and 89Sr was compared with the TS, Na 2Ti 2O 3SiO 4·2H 2O, having sitinakite topology. The Nb-TS shows significantly higher uptake value for 137Cs but lower for 89Sr than the TS. To investigate the origin of selectivity, the ion exchanged Cs + and Sr 2+ forms with the composition, Cs xNaH yNb 0.5Ti 1.5O 3SiO 4· zH 2O ( x=0.1, 0.2 and 0.3, x+ y=0.5 and z=1-2) and Sr 0.2Na 0.6H 0.5Nb 0.5Ti 1.5O 3SiO 4·H 2O, respectively, were structurally characterized from the X-ray powder diffraction data using the Rietveld refinement technique. Simultaneously the kinetics of 137Cs and 89Sr uptake was investigated for the Nb V free and doped samples. While the Cs + and Sr 2+ exchanged form of Nb-TS and the Cs + exchanged form of TS retain the symmetry of the parent compound, the Sr 2+ exchanged form of TS undergoes a symmetry change. The differences in the uptake of Cs + and Sr 2+ result from the different coordination environments of cesium and strontium in the eight-ring channel, that result from various hydration sites in the tunnel. The origin of selectivity appears to arise from the higher coordination number of cesium or strontium. Other effects due to Nb V substitution are reflected in the increase of both, the a- and c-dimensions and thus the unit cell volume, and the population of water vs. Na + in the channel to charge-balance the Nb 5+↔Ti 4+ substitution. 相似文献
9.
The effect of the acidity of the medium on the hydroxylation and nitration of alkanes (RH) in 90–98% H 2SO 4 at 25°C is described quantitatively by a model taking account of the thermodynamic activity of the RH, H 2O, and HSO 4- particles. It was concluded that in the transition states the reagents H 3O 2+HSO 4- and NO 2+ HSO 4- are present as HO + and NO 2+ ions without the bases H–O and HSO 4-, the alkanes are present without hydrophobic shells, and the initial reaction products are ROH 2+ and RNO 2H +. 相似文献
10.
The carbon cages composed of pentagons and heptagons (F 5F 7 isomers) are the analogs of fullerenes composed of pentagons and hexagons (F 5F 6 isomers). To provide insight into the structures and stability of the hydrides of F 5F 6 and F 5F 7 isomers, systematical density functional theory calculations are performed on all the 1,812 F 5F 6–C 60H 60 and 56 F 5F 7–C 60H 60. The calculated results demonstrate that the isomer with lowest/highest energy has most/fewest fused pentagons for both F 5F 6 and F 5F 7 hydrides and the stability of these hydrides increase with the number of fused pentagons roughly. The lowest energy F 5F 6–C 60H 60 and F 5F 7–C 60H 60 are 237.1 and 152.5 kcal/mol lower in energy than the isolated pentagon rule (IPR) C 60H 60, respectively; however, these two parent cages are 529.6 and 660.0 kcal/mol higher in energy than the IPR C 60. The calculations suggest that heptagon-containing cages, not only those violating the IPR can be the candidate cages for
fullerene derivatives and the possible repulsion between the added atoms may play an important role in determining the structures
and stability of the hydrides of carbon cages. 相似文献
11.
This work was focused on the influence of match degree of structure parameters i.e. molecular size, volume and polarity (denoted as Rd, Vd and Pd) between imprinted cavities in Qu-MIP and Xn on the adsorption selectivity. The results presented that the influence of Rd on the adsorption selectivity was the largest and the most regular, while the influence of Pd was the smallest and the most irregular. Besides, the influence degree of Vd was decreased in general with the increase of Rd. However, as Rd was in the threshold of [0.99, 1.02], Vd would rise to the major influence factor. Furthermore, utilizing data obtained from experiment, the influence authority of Rd, Vd and Pd on the adsorption selectivity was calculated theoretically through multiple linear regression and principal component analysis of IBM SPSS Statistics 20, and results showed the authority order was Rd, Vd and Pd at any circumstance despite the value was different, which was in accordance with the result we directly inducted from the experiment. 相似文献
12.
基于尖晶石晶体结构信息,本文采用热力学三亚晶格模型,将材料热力学计算和第一性原理计算相结合,研究了Zn_xMn_(1-x) Fe_2O_4和Ni_xMn_(1-x)Fe_2O_4立方相中的Zn~(2+)、Ni~(2+)、Mn~(2+)以及Fe~(3+)在8a和16d亚晶格上的占位有序化行为。结果表明:在锰铁氧体中,室温下Mn~(2+)完全占据在8a亚晶格上,Fe~(3+)完全占据在16d亚晶格上,属于正尖晶石结构;随着热处理温度升高,在1 273 K达到热处理平衡时的占位构型为(Fe~(3+)0.09Mn~(2+)0.91)[Fe~(3+)1.91Mn~(2+)0.09]O_4,在热处理温度升至1 473 K时,达到热处理平衡时的占位构型为(Fe~(3+)0.11Mn~(2+)0.89)[Fe~(3+)1.89Mn~(2+)0.11]O_4,均与实验结果符合较好。在锌铁氧体中,室温下Zn~(2+)完全占据在8a亚晶格上,Fe~(3+)完全占据在16d亚晶格上,属于正尖晶石结构;在热处理温度较高时,Zn~(2+)和Fe~(3+)发生部分置换,符合实验结果。在镍铁氧体中,半数的Fe~(3+)在室温下占据在8a亚晶格上,Ni~(2+)与剩下另一半的Fe~(3+)共同占据在16d亚晶格上,仅在热处理温度较高的时候发生微弱变化,亦与已有的实验结果吻合。在此基础上,本文进一步通过热力学模型研究了立方相尖晶石结构的Zn_xMn_(1-x)Fe_2O_4、Ni_xMn_(1-x)Fe_2O_4复合体系中阳离子占位行为与热处理温度对占位的影响规律。 相似文献
13.
Synthesis of a new donor, BEDT-HBDST and crystal structures, electrical and magnetic properties of (BEDT-HBDST)2MX4 (M=Fe, Ga, X=Cl, Br), where BEDT-HBDST=2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5-tetrahydrothiophene
A novel conjugation-elongated bis(ethylenedithio)tetraselenafulvalene (BETS) type donor, 2,5-bis(4,5-ethylenedithio-1,3-diselenol-2-ylidene)-2,3,4,5-tetrahydrothiophene (BEDT-HBDST) and its magnetic and non-magnetic anion salts, (BEDT-HBDST) 2MX4 ( MX4−=FeCl 4−, GaCl 4−, FeBr 4− and GaBr 4−), were prepared. These four salts are isostructural and belong to the space group of P2/ c. They showed semiconducting behavior with small activation energies (59-64 meV). The band structures of these salts are quasi one-dimensional and there is a midgap between the upper band and the lower band, since the degree of dimerization is significant in the stacking direction. The MX4− ions are located between the donor columns and near to the ethylenedithio moieties of the donor molecules. The magnetic susceptibilities of the FeCl 4− and FeBr 4− salts follow the Curie-Weiss law with Curie constants of 4.6 and 4.8 emu K mol −1 (sum of the spins of S=5/2 and S=1/2) and negative Weiss temperatures of θ=−1.2 and −4.9 K, respectively, revealing a weak antiferromagnetic interaction of 3d spins of the FeCl 4− and FeBr 4− anions. The Fe?Fe (6.66-7.60 Å), Cl?Cl (4.81-4.82 Å) and Br?Br (4.74-4.77 Å) distances in the crystal structures of these salts are significantly long. Therefore, the direct magnetic interaction between the 3d spins of the nearest neighboring Fe 3+ ions appears to be not readily accessible. 相似文献
14.
Phase equilibria in the reciprocal system 3Tl 2S + Sb 2Se 3 ? 3Tl 2Se + Sb 2S 3 are investigated by DTA, X-ray powder diffraction, and emf measurements. Some polythermal sections, the isothermal section of the phase diagram at 400K, and the liquidus-surface projection for this system are constructed. The types and coordinates of invariant and univariant equilibria are determined. It is shown that the system is non-diagonal. Broad regions of solid solutions are found on the basis of the binary compounds Tl 2S and Tl 2Se and along the boundary system Sb 2S 3-Sb 2Se 3 and the sections Tl 3SbS 3-Tl 3SbSe 3, TlSbS 2-TlSbSe 2, and TlSb 3S 5-TlSb 3Se 5 of the phase diagram. 相似文献
15.
In order to correct for neutron self-shielding in large-sample prompt gamma NAA, a method has been developed to determine
the macroscopic scattering and absorption cross sections, i.e., Σ
a and Σ
s, using four Cu flux monitors placed around the sample. With Monte Carlo computations, the neutron densities throughout the
sample and the resulting and the corresponding self-shielding factor as calculated from the Σ
a and Σ
s as obtained through the Cu monitors were compared to the true values. The derived Σ
a and Σ
s were found to be sufficiently accurate as long as Σ
t = Σ
a + Σ
s was less than 0.6 cm −1 and Σ
s/ Σ
t was greater than 0.1. 相似文献
16.
The relationship between the structure of monomer and kinetics of the radical polymerization of N-ethylmethacrylamide, N-butylmethacrylamide and N-phenylmethacrylamide in methanol and in dimethylsulphoxide was investigated. The reaction order with respect to initiator is 0·5 in all cases; the order with respect to monomer is independent of the type of substituent but depends on the solvent and on the viscosity of the reaction mixture. The polymerization rate, the value of , and the initiator efficiency decrease in the series N-phenylmethacrylamide, N-ethylmethacrylamide and N-butylmethacrylamide. The overall activation energy of polymerization for the monomers lies between 16 and 20 kcal/mol. 相似文献
17.
Abstract The apparent molar volume of quinic acid and its sodium salt were determined from the density data of aqueous solutions up
to molality of 0.4 mol kg −1 and in the temperature range from 293.15 to 328.15 K. The apparent molar volume of sodium quinate comprises the ionic and
the associated ion-pair contributions. From the apparent molar volumes of quinic acid and the quinate ion, the molecular contributions
to that of quinic acid are derived. At 298.15 K, the limiting apparent molar volume of quinic acid is 119.8 ± 0.5 cm 3 mol −1, and that of the quinic ion is 111.6 ± 0.3 cm 3 mol −1. Similarly, at 298.15 K, the limiting apparent molar expansibility of sodium quinate is 0.198 ± 0.003 cm 3 mol −1 K −1, and that of quinic acid is 0.142 ± 0.003 cm 3 mol −1 K −1. From these limiting ionic and molecular apparent molar volumes, the limiting volume change caused by ionization of quinic
acid was calculated as −8.2 cm 3 mol −1 at 298.15 K. The coefficients of thermal expansion of these solutions were calculated from the density data, and from these
the apparent molar expansibilities of quinic acid and its sodium salt were derived. 相似文献
18.
The synthesis of new chiral monomers ( M1 ? M3 ) based on menthol and the corresponding polyacrylates ( P1 ? P3 ) is described. The chemical structures, formula and phase behaviour of the obtained monomers and polymers were characterised with FT-IR, 1H-NMR, elemental analyses, differential scanning calorimetry (DSC), polarising optical microscopy (POM) and X-ray diffraction (XRD). The effect of the mesogenic core rigidity, spacer length and menthyl steric effect on the phase behaviour of M1 ? M3 and P1 ? P3 is discussed. The expected mesophase of the compounds based on menthol can be obtained by inserting a flexible spacer between the mesogenic core and the terminal groups. For the chiral monomers and polyacrylates, their corresponding melting temperature ( T m), glass transition temperature ( T g) and clearing temperature ( T i) increased with an increase of the mesogenic core rigidity; while the T m, T g and T i decreased with increasing the spacer length. M1 and P1 showed no mesophase, while M2 and M3 all revealed a SmC* and cholesteric phases. P2 and P3 only showed a cholesteric phase. 相似文献
19.
The electron paramagnetic resonance (EPR) parameters— g factors gi ( i = || and ⊥) and hyperfine structure constants Ai (M) and Ai(N), with M and N belonging to isotopes 63Cu 2+ and 65Cu 2+—and local structure of Cu 2+ ion occupying W 6+ site in CaWO 4 crystal are theoretically studied based on the perturbation formulas of these parameters for a 3d 9 ion under tetragonally elongated tetrahedra. In these formulas, the ligand orbital (LO) and spin–orbit coupling (SOC) contributions are included due to the shorter impurity-ligand distance R (≈1.83 Å) and hence the strong covalency of the studied [CuO 4] 6− cluster, and the related molecular orbital coefficients are quantitatively determined from the cluster approach in a uniform way; meanwhile, the required crystal field (CF) parameters for the tetragonally distorted tetrahedron (TDT) are estimated from the superposition model and the local structure of the impurity Cu 2+ center. According to the calculation, the bond angle θ between the four equivalent Cu 2+-O 2− bonds and the C 4 axis in the CaWO 4:Cu 2+ is found to be about 2.1° smaller than that ( θ0 ≈ 54.74°) for an ideal tetrahedron due to the Jahn–Teller (JT) effect and the size mismatch. The fitted results agree well with the observed values, and the validity of the present assignment for the local structure of the Cu 2+ center is also discussed. 相似文献
20.
The reaction of the [B 10H 9O 2C 4H 8] −, [B 10H 9OC 4H 8] −, and [B 10H 9OC 5H 10] − anions with negatively charged S-nucleophiles, such as SH −, SCN −, and S 2O 3
2−, resulted in the ring opening of the cyclic substituent and the formation of derivatives with the terminal thiol, thiocyanate,
and thiosulfate groups. The structures of the products were confirmed by the IR, mass, and 1H, 11B, and 13C NMR spectra. 相似文献
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