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1.
Single crystals of a new intermetallic gallide, R-CePd3Ga8, have been synthesized from excess molten gallium. Single-crystal X-ray diffraction reveals that R-CePd3Ga8 crystallizes in the R-3m space group with a=b=c=8.4903(10) Å and α=β=γ=89.993(17). R-CePd3Ga8 is a variant of the cubic BaHg11 structure type with three structural units: a Ce-centered polyhedron, a distorted cube of Pd2Ga6 and a Pd-centered cuboctahedron. The distortions of these units are compared to undistorted analogous units in intermetallic compounds with BaHg11 structure type. Field and temperature-dependent magnetization measurements on R-CePd3Ga8 reveal a paramagnetic material with strong antiferromagnetic correlations and a magnetization consistent with Ce3+. Electrical resistance measurements indicate Kondo behavior between localized Ce3+ magnetic moments.  相似文献   

2.
Mixed chromium-rhenium oxides, CrxRe1−xO2 with 0.31?x?0.66, have been synthesized for the first time by high-pressure high-temperature synthesis and in evacuated quartz tubes. The crystal structures of the compounds have been determined by single crystal and powder X-ray diffraction. Depending on synthesis conditions (pressure and temperature) these phases crystallize either in a tetragonal structure (P42/mnm) with statistical distribution of metal ions on one site (rutile-type), with cation ordering along c-axis (trirutile-type), or in a monoclinic rutile-like structure (C2/m) with ordering of Cr- and Re-cations and metallic Re-Re bonds. The “a” parameter of the tetragonal unit cell increases with increasing Re content whereas the “c” parameter decreases, indicating a strengthening of the Re-Re bond. The thermal stability of tetragonal CrxRe1−xO2 in Ar-atmosphere depends on the Re-content, decomposition is observed at 1241 K for x=0.34, but already at 966 K for x=0.5. The thermal expansion of CrxRe1−xO2 is anisotropic with a larger expansion coefficient in the “c” direction. Tetragonal CrxRe1−xO2 with 0.31?x<0.54 order antiferromagnetically at low temperatures with TN depending on the Cr-content x.  相似文献   

3.
The K shell X-ray intensity ratios Kα2/Kα1, Kβ1,3/Kα1 and Kβ2/Kα1 for 21 elements with 65⩽Z⩽92 have been measured using an incident photon energy of 123.6 keV. The X-rays have been measured with a Si(Li) semiconductor detector. Kβ and Kα X-rays have been analyzed into the components Kβ1,3 and Kβ2 and Kα1 and Kα2, respectively, using a computer program. The experimental results were compared with the theoretical values of Scofield and available experimental results. All X-ray intensity ratios values have been plotted versus atomic number.  相似文献   

4.
The crystal structure of our newly discovered Sr-Co-O phase is investigated in detail through high-resolution electron microscopy (HREM) techniques. Electron diffraction (ED) measurement together with energy dispersive X-ray spectroscopy (EDS) analysis show that an ampoule-synthesized sample contains an unknown Sr-Co-O ternary phase with monoclinic symmetry and the cation ratio of Sr/Co=1. From HREM images a layered structure with a regular stacking of a CdI2-type CoO2 sheet and a rock-salt-type Sr2O2 double-layered block is observed, which confirms that the phase is the parent of the more complex “misfit-layered (ML)” cobalt oxides of [MmA2Om+2]qCoO2 with the formula of [Sr2O2]qCoO2, i.e. m=0. It is revealed that the misfit parameter q is 0.5, i.e. the two sublattices of the CoO2 sheet and the Sr2O2 block coexist to form a commensurate composite structure. We propose a structural model with monoclinic P21/m symmetry, which is supported by simulations of ED patterns and HREM images based on dynamical diffraction theory.  相似文献   

5.
Vibrational frequencies vOH and vOD have been measured for isotopically-dilute HDO molecules in eleven solid hydrates at 90 K. The results have been used to prepare a plot of the ratio vOH/vOD versus vOH. The ratios fall on a smooth curve and decrease with decreasing frequencies vOH. The anharmonicity constants ωexe have been estimated. They were found to increase with decreasing vOH.  相似文献   

6.
NMR measurements have been used to characterize the electron-beam (EB) induced polymerization of 1,6-hexanediol diacrylate. Hydrogen T1, T, and T2 values have been measured as a function of radiation dose. The T2 signal consists of a Gaussian component and a longer component consisting of two exponentials. The sum of the Gaussian and the short exponential intensities is strongly correlated with the polymer fraction determined by gel extraction. T2 values associated with the exponential component decrease rapidly with increasing dose. The T1 relaxation consists of two exponentials for low dose and a single exponential for high dose. The T relaxation consists of from two to three exponential components, and the departure from a single exponential decreases with increasing dose. T1 and T intensities are poorly correlated with gel extraction results. T1 and T minima occur at intermediate radiation dose, and T depends on H1 at high dose. Limited spin diffusion plays an important role in the T1 and T relaxation. Hydroquinone has little effect on the EB-induced polymerization.  相似文献   

7.
Large single crystals from RENi2-xP2 (RE=La, Ce, Pr) were synthesized from the pure elements using Sn as a metal flux, and their structures were established by X-ray crystallography. The title compounds were confirmed to crystallize in the body-centered tetragonal ThCr2Si2 structure type (space group I4/mmm (No. 139); Pearson's symbol tI10), but with a significant homogeneity range with respect to the transition metal. Systematic synthetic work, coupled with accurate structure refinements indicated strong correlation between the degree of Ni-deficiency and the reaction conditions. According to the temperature dependent dc magnetization measurements, LaNi2-xP2 (x=0.30(1)), as expected, is Pauli-like paramagnetic in the studied temperature regime, while the Ce-analog CeNi2-xP2 (x=0.28(1)) shows the characteristics of a mixed valent Ce3+/Ce4+ system with a possible Kondo temperature scale on the order of 1000 K. For three different PrNi2-xP2 (x?0.5) samples, the temperature and field dependence of the magnetization indicated typical local moment 4f-magnetism and a stable Pr3+ ground state, with subtle variations of TC as a function of the concentration of Ni defects. Field-dependent heat capacity data for CeNi2-xP2 (x=0.28(1)) and PrNi2-xP2 (x=0.53(1)) are discussed as well.  相似文献   

8.
Apparent molar volumes Vφ and apparent molar heat capacities Cp,φ were determined for aqueous solutions of l-proline, l-proline with equimolal HCl, and l-proline with equimolal NaOH at the pressure p=0.35 MPa. Density measurements obtained with a vibrating-tube densimeter at temperatures (278.15⩽T/K⩽368.15) were used to calculate Vφ values, and heat capacity measurements obtained with a twin fixed-cell, differential-output, power-compensation, temperature-scanning calorimeter at temperatures (278.15⩽T/K⩽393.15) were used to calculate Cp,φ values. Speciation arising from equilibrium was accounted for using Young’s Rule, and semi-empirical equations describing (Vφ, m, T) and (Cp,φ, m, T) for each aqueous equilibrium species were fitted by regression to the experimental results. From these equations, the volume change ΔrVm and heat capacity change ΔrCp,m for the protonation and deprotonation reactions were calculated. Additionally, the ΔrCp,m expression was integrated symbolically to yield values of the reaction enthalpy change ΔrHm, reaction entropy change ΔrSm, and equilibrium molality reaction quotient Q for both reactions. The results provide a much-improved thermodynamic characterization of aqueous l-proline and of its protonation and deprotonation equilibria.  相似文献   

9.
Single crystals of PrO2 and of the oxygen deficient fluorite related phase TbO2−x have been obtained by anodic electrocrystallization from alkaline hydroxide melts containing PrCl3 and TbCl3, respectively. Magnetic measurements, X-ray diffraction data and TEM investigations confirm the identity of the products. PrO2 crystallizes in a fluorite type of structure with a=5.3945(3) Å and shows paramagnetic behaviour with a magnetic moment as expected for Pr4+ (μeff=2.49μB, Θ=−109 K, TN=10 K). According to precession photographs and an examination with an area sensitive X-ray detector, TbO2−x exhibits a superstructure of fluorite with a pseudocubic subcell with af=5.2810(1) Å. This lattice constant is intermediate between those of TbO2 and Tb2O3 (C-type), the same is true for its paramagnetic behaviour (μeff=8.58μB, Θ=−22 K, TN=5 K). The supercell was found to be hexagonal with a=25.836(1) Å and c=36.672(2) Å, the symmetry of the intensity distribution being monoclinic. Electron diffraction revealed a cubic cell with a=10.6 Å, space group Ia-3, indicating reduction of the material in the electron beam.  相似文献   

10.
Total collision cross section measurements with a state selected H2 beam are discussed in terms of a V2 (R) P2 (cos?) angle dependent part of the intermolecular potential. It is shown that the V2 (R) factor has a shallow minimum ?2 of about 10% of the angle averaged well depth ?; its position Re2 is displaced a few percent to larger distances, with respect to the position Re of the angle averaged minimum.  相似文献   

11.
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   

12.
The structures of recently discovered new high-temperature modifications of cobalt molybdate, a′-and a″-CoMoO4, were determined. a′-and a″-CoMoO4 appear after the phase a-CoMoO4 is heated above the temperature range 700–1000°C. They seem to be the disordered modifications of a-CoMoO4 with metal atoms distributed at random in an a-CoMoO4 oxygen network.The F(hkl) values, calculated for variously disordered a-CoMoO4 structure, were compared with the observed intensities of diffraction lines changing in the course of aa′ and aa″ transitions. It was concluded that a″-CoMoO44 has a completely disordered structure with random distribution of both Co and Mo atoms in oxygen interatomic voids. The a′-CoMoO4 is a partly disordered modification, with random distribution of some cations only.The temperature and the kind of order-disorder transition depend on the method of preparation of a-CoMoO4 samples.The disordered modifications of cobalt molybdate may be supercooled—even to room temperature—before it transforms rapidly into low-temperature b-CoMoO4 form.  相似文献   

13.
The article aims to outline the growth of evidence and ideas about infrared band broadening for simple, gaseous, moderately strong, hydrogen bonded dimers B…HA, to draw attention to areas in need of further development and to collect together experimental information available at the present time about vibrational states associated with such dimers. The band associated with the modified HA stretching mode, νs, is observed for several dimers not only to be broad, but to have sub-band structure, which is satisfactorily interpreted as arising from combination bands of νs with the low frequency stretch-mode νσ, giving a progression νs ± σ as a result of strong anharmonic coupling. For weaker dimers with lower values of νσ the sub-band structure is less evident, and may appear only as shoulders, while for still weaker dimers, the sub-bands may be merged into a featureless broad band. A major factor contributing to the breadth of the individual sub-bands in the band structure is the presence of hot-bands, especially a long series based on successive excited states of the low-frequency bending mode νβ. A link is indicated with the interpretation of band-broadening for moderately strong hydrogen-bonded complexes in the liquid state. The anharmonic coupling of νs and νσ is again a central feature but there is a new factor, namely the coupling of νσ through a fluctuating potential with the surroundings, which has the result that the νs mode rapidly loses phase coherence resulting in a broad structureless band.  相似文献   

14.
The low-resolution mass spectra of 13 trifluoromethyl and/or methyl sulfur-containing compounds (CF3SnCF3, CF3SnCH3, CH3SnCH3, CF3SmCl, and CH3SmCl; n = 1, 2, 3; m = 1, 2) are reported and discussed. There is a considerable similarity between the fragmentation pattern of compounds with the same terminal groups. However, with a fluorinated and a non-fluorinated methyl group, the major fragmentation products produced are similar to those for the dimethyl compounds.  相似文献   

15.
Magnetic and electron transport properties of four series of manganates of the composition La0.5−xLnxSr0.5MnO3 (Ln=Pr, Nd, Gd and Y) have been investigated to examine how the ferromagnetic metallic nature of the parent La compound changes over to antiferromagnetic insulating behavior, with change in Ln and x due to the associated changes in the A-site cation radius as well as the size disorder. When Ln=Pr and Nd, there is a transition from the tetragonal I4/mcm structure to the orthorhombic Immm and Imma structures at x=0.2 and 0.35, respectively. There is a gradual evolution of the properties from those of La0.5Sr0.5MnO3 to those of Pr0.5Sr0.5MnO3 or Nd0.5Sr0.5MnO3 with increase in x. Thus, when x>0.2 and >0.35, respectively, the Pr- and Nd-substituted manganates show ferromagnetic transitions followed by antiferromagnetic transitions at low temperatures, with the ferromagnetic TC decreasing with increasing x. The Gd and Y series of compounds are all orthorhombic and show a decrease in TC with the increase in x, the ferromagnetism disappearing at high x. At a value of x corresponding to the A-site cation radius of Pr0.5Sr0.5MnO3, the Gd and Y series of compounds exhibit ferromagnetism in the 250-300 K region and undergo an antiferromagnetic transition on cooling. The TCTN gap is sensitive to the disorder arising from the size mismatch.  相似文献   

16.
The magnetic properties of a series of cubic perovskite materials, Eu(Al0.5Ta0.5)O3, Eu(Mg0.5W0.5)O3, and Eu(Lu0.5Ta0.5)O3 have been investigated using bulk magnetic and Mössbauer techniques. Eu(Al0.5Ta0.5)O3 is a ferromagnet (Tc ~ 5°K, θc = + 8°K), Eu(Lu0.5Ta0.5)O3 is an antiferromagnet (TN = 4.0, θc = ?8°K), while Eu(Mg0.5W0.5)O3 is probably antiferromagnetic (TN = 2.8°K, θc = ? 1°K). These data are compared with the known properties of EuLiH3 and EuTiO3 and a sharp drop in θc as a function of increasing lattice constant is noted. A molecular field theory analysis of the data yields two possible sets of nn (J1) and nnn (J2) exchange constants for each compound which are compared with existing theories.  相似文献   

17.
Perovskite-type cobaltates in the system La2Co1+z(MgxTi1−x)1−zO6 were studied for z=0≤x≤0.6 and 0≤x<0.9, using X-ray and neutron powder diffraction, electron diffraction (ED), magnetic susceptibility measurements and X-ray absorption near-edge structure (XANES) spectroscopy. The samples were synthesised using the citrate route in air at 1350 °C. The space group symmetry of the structure changes from P21/n via Pbnm to Rc with both increasing Mg content and increasing Co content. The La2Co(MgxTi1−x)O6 (z=0) compounds show anti-ferromagnetic couplings of the magnetic moments for the Co below 15 K for x=0, 0.1 and 0.2. XANES spectra show for the compositions 0≤x≤0.5 a linear decrease in the L3/(L3+L2) Co-L2,3 edge branching ratio with x, in agreement with a decrease of the average Co ion spin-state, from a high-spin to a lower-spin-state, with decreasing nominal Co2+ ion content.  相似文献   

18.
Intercalation behavior of n-alkylamines into a protonated form of an A-site defective layered perovskite H2W2O7 has been investigated. Results from XRD indicate these materials are layered with the corresponding interlayer spacing governed by the n-alkylamine chain length, and a reversible intercalation and deintercalation property is observed among these intercalation compounds. The IR spectra of the intercalation compounds with n-alkylamines clearly show that n-alkyl chains possess an all-trans conformation, and H2W2O7 accommodate n-alkylamines (CnH2n+1NH2: n=3, 4, 7, 8, 12, 16) to form intercalation compounds via an acid-base mechanism. A linear relationship between the interlayer distance and the number of carbon atoms in n-alkyl chains is observed to show a bilayer arrangement of the n-alkyl chains with a tilt angle of ∼71.6°. Elemental analysis studies reveal that the amounts of intercalated n-alkylamines are about 2.0 mol per [W2O7]. Despite the surface geometry of H2W2O7 is almost identical to those of layered perovskites H2[An−1BnO3n+1], the amounts of intercalated n-alkylamines of them are different. A reasonable explanation is given through our research.  相似文献   

19.
The temperature dependence of the paramagnetic susceptibility χm(T) taken in 2500 Oe, the resistivity ρ(T), and the thermoelectric power α(T) of DyBaCo2O5+x, which has Ba and Dy ordered into alternate (001) planes of an oxygen-deficient perovskite, have revealed a phase segregation in the compositional range 0.3?x<0.5. Orthorhombic DyBaCo2O5.51 has, in addition, oxygen vacancies ordered into alternate rows of the DyO0.51 (001) planes; a cold-pressed polycrystalline sample exhibits a first-order insulator-metal transition at TIM=320 K, a Curie temperature TC=300 K, and a broadened metamagnetic transition temperature TM≈265 K in 2500 Oe. A ferromagnetic M-H hysteresis curve fails to saturate at 5 T, and a minority ferromagnetic phase below TM has a volume fraction that decreases with decreasing temperature, vanishing below 50 K. Oxygen vacancies in the DyBaCo2O5.5 phase suppress the metallic state; interstitial oxygen does not. A thermoelectric power α(T)>0 of DyBaCo2O5.51 changing continuously across TIM is interpreted to manifest a metallic minority phase crossing a percolation threshold; α(T) also provides evidence for a progressive excitation of higher-spin Co(III) with increasing temperature from below 50 K to above TIM. A previous model of the RBaCo2O5.5 phase is extended to account for the Ising spin configuration below TC, the magnetic order in the presence of higher-spin octahedral-site Co(III), and the α(T) data.  相似文献   

20.
Series of compounds in the system NaxNbyW1−yO3 were prepared according to the appropriate molar ratio of Na2WO4, WO3, WO2 and Nb2O5 with x=0.80 and 0.0?y?0.4 at 600 °C in evacuated silica glass tubes. These compounds were investigated by X-ray powder diffraction, optical microscopy, microprobe analysis, Raman and optical microspectroscopy. A y-dependent separation into three distinct coloured crystallites with cubic perovskite-type structures is observed: (i) red-orange crystallites with composition NaxWO3 with slightly decreasing x (i.e. 0.8-0.72) with increasing nominal y, (ii) bluish solid solution of composition NaxNbyW1−yO3 and (iii) white crystallites of a new phase having defect perovskite-type structure with composition Na0.5NbO2.75.  相似文献   

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