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1.
The crystal structure of the hexagonal phase KxVxMo1?xO3 (x = 0.13) has been determined by single crystal X-ray analysis. The space group is P63. The parameters are a = 10.481 Å and c = 3.701 Å. The structure is formed by triple chains of octahedra sharing corners and parallel to the Oz axis. Each triple chain shares edges with three other chains.Potassium is inserted in the large tunnels. The reliability factor is R = 0.045 on the base of 158 observed reflexions. The RbxVxMo1?xO3 and CsxVxMo1?xO3 phases (0.12 ? x ? 0.14) are isostructural with KxVxMo1?xO3. 相似文献
2.
Ş. Erkoç 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1991,19(4):423-425
The structural stability and energetics of carbon, silicon, and germanium microclusters containing 3?7 atoms have been investigated by using a recently developed empirical many-body potential energy function (PEF), which comprises two- and three-body atomic interactions. The PEF satisfies both bulk cohesive energy per atom and bulk stability exactly. It has been found that the most stable C3?4 microclusters are linear withD ∞h symmetry but C5?7 microclusters are planar withD nh symmetry. Silicon and germanium microclusters show similar structural stability. TheX n (X=Si, Ge;n=3?7) microclusters are found to be most stable in the following forms:X 3 is triangular withD 3h symmetry,X 4 is tetragonal withT d symmetry,X 5 is square pyramidal withD 4h symmetry,X 6 is bipyramidal square withO h symmetry, and finallyX 7 is square pyramidal having two atoms underneath withD 2h symmetry. 相似文献
3.
E. F. Kustov V. I. Nefedov M. S. Karelina E. V. Shul’gina G. S. Chernova 《Russian Journal of Inorganic Chemistry》2007,52(2):218-224
The formulas for calculation of the composition of nanoparticles with symmetry group T d are reported. The numbers of atoms in the shells of tetrahedral symmetry are determined by three structurally invariant numbers and the “quantum number” of the group order n. Four classes of all possible nanostructures with symmetry group T d are revealed: C ? + 12z , where z = 0, 1, 2, ..., and C ? is C 4, C 6, C 8, C 10, or C 14. The sum rule for the coordination numbers of the shell sites located on the axes of symmetry is obtained. The six-shell periodicity of the number of occupied sites located on the symmetry axes and in symmetry planes is revealed. 相似文献
4.
《Electrochemistry communications》2000,2(4):262-266
The characterisation of the transport and interfacial reaction of electrons in dye-sensitised nanocrystalline solar cells is complicated by the non-linearity of these processes. This problem has been overcome by superimposing small amplitude pulsed laser excitation on steady background illumination. The laser perturbation of the photostationary state is sufficiently small that the photocurrent and photovoltage responses can be fitted using constant values of the electron diffusion coefficient Dn and electron lifetime τn. Analytical and finite difference solutions of the continuity equation have been used to analyse the experimental photocurrent, photocharge and photovoltage transients, and the intensity dependence of Dn and of τn has been established by varying the bias illumination level, and hence the dc photocurrent density, jdc. The intensity dependence of Dn (Dn∝jdc0.68) is attributed to trapping/detrapping involving a distribution of trapping levels. The intensity dependence of τn (τn∝jdc−0.62) may indicate that the back reaction of electrons with I3− is not first order in electron concentration. Other possible explanations are that the interfacial electron transfer rate constant depends on trap occupancy or on the rate of surface or bulk electron diffusion. 相似文献
5.
J.A. ColladoM.A.G. Aranda A. CabezaP. Olivera-Pastor S. Bruque 《Journal of solid state chemistry》2002,167(1):80-85
The La2W2−xMoxO9 series has been synthesized by the ceramic method. An alternative synthesis using microwave radiation is also reported. La2W2O9 has two polymorphs and the low-temperature phase (α) transforms to the high-temperature form (β) at 1077°C. The influence of the W/Mo substitution in this phase transition has been investigated by DTA. The β structure for x≥0.7 compositions can be prepared as single phase at any cooling rate. The β phase for 0.3≤x≤0.7 compounds can be prepared as single phase by quenching, whereas a mixture of α and β phases is obtained by slow cooling. The W/Mo ratio in both coexisting phases is different with the β-phase having a higher Mo content. The x=0.1 and 0.2 compounds have been prepared as mixtures of phases. The room temperature structure of β-La2W1.7Mo0.3O9 has been analyzed by the Rietveld method in P213 space group. The final R-factors were RWP=9.0% and RF=5.6% with a structure similar to that of β-La2Mo2O9. Finally, the thermal expansion of both types of structures has been determined from a thermodiffractometric study. The thermal expansion coefficients were 2.9×10−6 and 9.7×10−6°C−1 for α-La2W2O9 and β-La2W1.2Mo0.8O9, respectively. 相似文献
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7.
The subsolidus phase relations of R2O3-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca14−xRxCu24O41 (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca2+xR2−xCu5O10 (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca14−xRxCu24O41 possesses a layered orthorhombic structure and is isostructural to Sr14−xCaxCu24O41. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca2+xR2−xCu5O10 solid solution is isostructural to Ca2+xY2−xCu5O10, the structure of which is based on an orthorhombic “NaCuO2-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels. 相似文献
8.
《Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy》1980,36(7):699-704
The 31P chemical shift of the (C6H5)3−nPRn and (C6H5)3−nPRnCr(CO)5 (n = 0–3; R H, CH3, C2H5, i-C3H7, t-C4H9) derivatives is dominated by the steric effect. A small inductive effect is also operative but there are no indications of notable (dCr→dP)π back-bonding. The 13C chemical shift of the phenyl carbon atoms indicates that (pring-dP)π electron delocalization is unimportant.The 13C chemical shift of the carbonyl carbon atoms, which is mainly governed by the mean excitation energy, confirms the conclusion that there are no notable changes in (dCr→dP)π back-bonding in this series of compounds. 相似文献
9.
The aqueous synthesis and electrochemical properties of nanocrystalline MxV2O5Ay·nH2O are described. It is easily and quickly prepared by precipitation from acidified vanadate solutions. MxV2O5Ay·nH2O has been characterized by X-ray powder diffraction, electron microscopy, TGA, chemical analyses, and electrochemical studies. The atomic structure is related to that of xerogel-derived V2O5·nH2O. In MxV2O5Ay·nH2O, M is a cation from the starting vanadate salt and A is an anion from the mineral acid. This material exhibits high, reversible Li capacity and may be considered for use in a cathode in primary and secondary batteries. The lithium capacity of an electrode composed of MxV2O5Ay·nH2O/EPDM/carbon (88/4/8) is ∼380(mA h)/g (C/80 rate) and the energy density is ∼1000(W h)/kg (120-μm-thick cathode, 4-1.5 V, versus Li metal anode). Critical parameters identified in the synthesis of MxV2O5Ay·nH2O, with respect to achieving high Li-ion insertion capacity, are acid/vanadium ratio, starting vanadate salt, and temperature. Inclusion of carbon black in the synthesis yields a composite that maintains the high Li capacity, lowers the electrochemical-cell polarization, and preserves the lithium capacity at higher discharge rates. Li-ion coin cells, using pre-lithiated graphite anodes, exhibit electrochemical performance comparable to that of Li-metal coin cells. 相似文献
10.
The 1H and 87Rb spin-lattice relaxation and spin-spin relaxation times in superionic Rb3H(SeO4)2 single crystals grown by the slow evaporation method were measured over the temperature range 160-450 K. The temperature dependencies of the 1H T1, T1ρ, and T2 are measured. In the ferroelastic phase, T1 differs from T1ρ, which is in turn different from T2, although these three relaxation times converge to similar values near 410 K. This transition seems to occur at temperature which is about 40 K lower than the superionic transition temperature. The observation of liquid-like values of the 1H T1, T1ρ, and T2 in the high temperature is compatible with the phase being superionic, indicating that the destruction and reconstruction of hydrogen bonds does indeed occur at high temperature. In addition, the 87Rb T1 and T2 values at high temperature were similar (on the order of milliseconds), a trend that was also observed for 1H T1 and T2. This behavior is expected for most hopping-type ionic conductors, and could be attributed to interactions between the mobile ions and the neighboring group ions within the crystal. The motion giving rise to this liquid-like behavior is related to the superionic motion. 相似文献
11.
Hong Chang Yong-quan Guo Quan-lin Liu Jing-kui Liang Guang-hui Rao 《Journal of solid state chemistry》2004,177(11):4341-4345
The structure and magnetic properties of the RCo5Ga7 (R=Y, Tb, Dy, Ho and Er) compounds with the ScFe6Ga6-type structure have been studied. The stability of RCo5Ga7 is closely related with the ratio of the metal radii RRE/R(Co,Ga). With RRE/R(Co,Ga)?1.36, the compounds can be stabilized in the ScFe6Ga6-type structure. The lattice of RCo5Ga7 shrinks as the atomic order of R increases, and it is consistent with the lanthanide contraction. The structure analysis based on X-ray diffraction patterns reveals that in the orthorhombic RCo5Ga7 (Immm), R occupies the 2a site, and Co enters into the 8k and the 4h sites, and Ga is at the 4e, 4f, 4g, 4h and 8k sites. The interatomic distances and the coordination numbers of RCo5Ga7 are provided from the refinement results. The short interatomic distance (less than 2.480 Å) between the Co ions results in the negative magnetic interaction, which does not favor ferromagnetic ordering. The magnetic moment of YCo5Ga7 is absent, and RCo5Ga7 (R=Tb, Dy, Ho and Er) may have long-range magnetic ordering with the paramagnetic Curie temperature lower than 5 K. 相似文献
12.
Keeyung Lee 《Zeitschrift für Physik D Atoms, Molecules and Clusters》1997,40(1):164-166
The electronic structure and magnetism of 13 atom clusters of ruthenium, rhodium and palladium having face centered cubic(fcc) geometry has been studied using a Gaussian orbital basis and the local spin density approximation. Calculations were done for the lattice spacings relevant to the bulk crystal lattice. Using the fixed moment states as input potentials, as many as 3 self-consistent states were obtained for these clusters. The 3 converged states of Rh13 cluster is found to have magnetic moments of 0.69 μB , 1.00 μB and 1.46 μB . Out of these states, 0.69 μB moment state is found to be the ground state. But the total energy difference between the 0.69 μB and 1.00 μB state is very small. The 1.46 μB moment state coincides with the state reported previously by other authors which was obtained using the discrete variational method. The experimentally observed moment was around 0.47 μB . Our calculated moment is closer to the experimentally observed moment than the previously reported moment, but is still a bit larger. Ru13 cluster is also found to have large moments, and 3 self-consistent states are also obtained for this cluster. The 3 magnetic moments of the Ru13 cluster are 0.46 μB , 0.62 μB and 1.08 μB . Out of these states, 0.62 μB moment state is found to be the ground state. For the Pd13 cluster, in addition to the nonmagnetic state previously reported, a state with magnetic moment of 0.46 μB is also found to exist indicating possible magnetism in cluster phase. 相似文献
13.
《Journal of Inorganic and Nuclear Chemistry》1978,40(4):683-686
The comparative extraction behavior of tracer-level UO22+ into benzene solutiosn of two highly sterically hindered extractants, di(2,6-di-iso-propyl phenyl) phosphoric acid, HD(2,6-i-PΦ)P and di-tertiary-butyl phosphinic acid, H[Dt-BP], vs an aqueous 1.0 F (NaCl + HCl) phase was studied. The extraction of UO22+ in both systems is directly second-power dependent upon extractant concentration and inversely second-power dependent upon hydrogen ion concentration, the stoichiometry of extraction being UO2A2++2(HY)20 ⇆ UO2(HY2)20 + 2HA+ The expression for the distribution ratio, K, is K=K5F2/[H+]2 the general expression for the extraction of any metallic species being K=K5Fa/[H+]b where Ks is a constant characteristic of the system, F the concentration in formality units of extractant in the organic phase, [H+] the concentration of hydrogen ion in the aqueous phase, and a and b the respective extractant and hydrogen-ion dependencies.Both extractants have a high degree of steric hindrance. The HD(2,6-i-PΦ)P is the more highly acidic, the pKA value, in 75% ethanol, being 3.2. The pKA, previously reported, for H[Dt-BP] is 6.26. The Ks for UO22+ in the system HY in benzene diluent vs an aqueous 1.0 F (NaCl + HCl) phase is 2 × 104 for H[Dt-BP] and 3 × 10−1 for HD(2,6-i-PΦ)P; the ratio of the Ks values, nearly 7 × 103, favors the less acidic extractant. For comparative purposes, the Ks values for UO22+ and for Eu3+ in other (X1)(X2)PO(OH), in benzene diluent vs 1.0 F (NaCl + HCl) systems are presented. The variations are discussed in terms of the pKA of the extractant and the steric hindrance within the extractant. 相似文献
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15.
Nanostructured perovskite-type Sr1−aCeaFeO3−x, (0?a<0.15) powders have been prepared by citrate-nitrate smoldering auto-combustion. Their phase structure and stability, surface and morphological properties, reduction behavior and interaction with oxygen have been investigated by X-ray Powder Diffraction combined with Rietveld Analysis, 57Fe Mössbauer and X-ray Photoelectron Spectroscopies, N2-adsorption method, Temperature Programmed Reduction and Oxidation experiments. Our results reveal that citrate-nitrate auto-combustion method is effective in obtaining single phase Sr1−aCeaFeO3−x. The Sr1−aCeaFeO3−x structure is cubic only for a?0.06, while for a<0.06 remains tetragonal. Moreover, for a?0.06 after semi-reductive treatment under inert gas, an expanded cubic phase is obtained instead of the brownmillerite-type structure, which is known to have ordered vacancies. Stabilization of octahedral Fe3+ by cerium doping appears to be the main factor in determining the structural properties of Sr1−aCeaFeO3−x. The highest oxygen consumption for Ce-doped SrFeO3 occurs for a=0.06. Preliminary impedance measurements show that Sr0.94Ce0.06FeO3−x has the lowest area-specific resistance. 相似文献
16.
Titanates de cuivre substitués à structure bixbyite: Les composés Cu1−xTi1−xFe2xO3 (0.15 ≤ x ≤ 0.33)
A new bixbyite family, Cu1?xTi1?xFe2xO3 (0.15 ≤ x ≤ 0.33) has been synthesized and characterized. The unit cell is cubic: a ~ 9.40Å. The X-ray powder diffraction study shows up an isotypism with the (Fe, Mn)2O3 compounds. There is a disordered distribution of CuII, TiIV, and FeIII over the two cyrstallographic sites: PI and PII. PII is highly distorted (two long MO distances) by the Jahn-Teller effect of CuII. The bixbyite structure is described in terms of polyhedra arrangement, as a particular case of the CM2O3 family. The cation packing is discussed in relation with the existence of the bixbyite structure for the Cu1?xTi1?xFe2xO3 compounds. The electrical properties (σ ~ 10?5(Ω cm)?1 for x = 0.286 at room temperature) show an electron conduction with probably a hopping mechanism. 相似文献
17.
《Spectrochimica Acta Part B: Atomic Spectroscopy》2007,62(6-7):529-532
A different approach to X-ray stress analysis has been developed. At the outset, it must be noted that the material to be analyzed is assumed homogeneous and isotropic. If a sphere with radius r within a specimen is subjected to a state of stress, the sphere is deformed into an ellipsoid. The semi-axes of the ellipsoid have the values of (r + εx), (r + εy), and (r + εz), which are replaced by dx, dy, and dz, or for the cubic case, ax, ay, and az. In this technique, at a particular ϕ angle (see Fig. 1), the two-theta position of a high angle (hkl) peak is determined at ψ angles of 0, 15, 30, and 45°. These measurements are repeated for 3 to 6 ϕ angles in steps of 30°. The dϕψ or aϕψ values are then determined from the peak positions. The data is then fitted to the general quadratic equation for an ellipsoid by the method of least squares. From the coefficients of the quadratic equation, the angle between the laboratory and the specimen coordinates (direction of the principle stress) can be determined. Applying the general rotation of axes equations to the quadratic, the equation of the ellipse in the x–y plane is determined. The ax, ay, and az values for the principal axes of the lattice parameter ellipsoid are then evaluated. It is then possible to determine the unstressed a0 value from Hooke's Law using ax, ay, and az. The magnitude of the principal strains/stresses is then determined. 相似文献
18.
V. P. Korolev 《Journal of Structural Chemistry》2010,51(3):491-499
The partial volume -V 2 0 of amino acids in aqueous solution is assumed to be zero for T = 227 K (singular temperature) and T= T c (critical temperature). The literature data for -V 2 0(T) of ten amino acids at 278–328 K are reproduced by the two-parameter equation with a standard deviation of 0.06–0.16 cm3/mol. Only for asparagine and tryptophan the standard deviation exceeds 0.3 cm3/mol. In the case of glycine and alanine, the relation -V 2 0(T) in the high temperature range is obtained. -V 2 0 is divided into contributions (?-H 2 0/?p) T and —T·(?-S 2 0/?p) T . Their dependence on the temperature and amino acid nature is discussed. Positive values of ?-C 2 0/?p) T characterize amino acids as water structure breakers; however, the differentiation of compounds by this feature is not successful. The behavior of amino acids in aqueous solutions is compared with the behavior of urea. 相似文献
19.
A Lainez Emmerich Wilhelm G Roux-Desgranges J.-P.E Grolier 《The Journal of chemical thermodynamics》1985,17(12):1153-1161
Excess molar volumes VmE at 298.15 K were obtained, as a function of mole fraction x, for series I: {x1-C4H9Cl + (1 ? x)n-ClH2l + 2}, and II: {x1,4-C4H8Cl2 + (1 ? x)n-ClH2l + 2}, for l = 7, 10, and 14. 10, and 14. The instrument used was a vibrating-tube densimeter. For the same mixtures at the same temperature, a Picker flow calorimeter was used to measure excess molar heat capacities Cp, mE at constant pressure. VmE is positive for all mixtures in series I: at x = 0.5, VmE/(cm3 · mol?1) is 0.277 for l = 7, 0.388 for l = 10, and 0.411 for l = 14. For series II, VmE of {x1,4-C4H8Cl2 + (1 ? x)n-C7H16} is small and S-shaped, the maximum being situated at xmax = 0.178 with VmE(xmax)/(cm3 · mvl?1) = 0.095, and the minimum is at xmin = 0.772 with VmE(xmin)/(cm3 · mol?1) = ?0.087. The excess volumes of the other mixtures are all positive and fairly large: at x = 0.5, VmE/(cm3 · mol?1) is 0.458 for l = 10, and 0.771 for l = 14. The Cp, mEs of series I are all negative and |Cp, mE| increases with increasing l: at x = 0.5, Cp, mE/(J · K?1 · mol?1) is ?0.56 for l = 7, ?1.39 for l = 10, and ?3.12 for l = 14. Two minima are observed for Cp, mE of {x1,4-C4H8Cl2 + (1 ? x)n-C7H16}. The more prominent minimum is situated at x′min = 0.184 with Cp, mE(x′min)/(J · K?1 · mol?1) = ?0.62, and the less prominent at x″min = 0.703 with Cp, mE(x″min)/(J · K?1 · mol?1) = ?0.29. Each of the remaining two mixtures (l = 10 and 14) has a pronounced minimum at low mole fraction (xmin = 0.222 and 0.312, respectively) and a broad shoulder around x = 0.7. 相似文献