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1.
2.
Density functional calculations on the electronic structure and magnetic properties of Ni5 and Ni6 clusters are presented in this work. The geometry and spin state of clusters are optimized for several starting symmetries. Moreover, those calculations are followed by a vibrational analysis to discriminate between real minima and saddle-points on the potential energy surface of clusters. Equilibrium geometries, electronic configurations, binding energies, magnetic moments, and harmonic frequencies of stable Ni5 and Ni6 clusters are reported.  相似文献   

3.
The skutterudite-related material CoGe1.5Te1.5 has been synthesised and structurally characterised by powder neutron diffraction. Analysis of the high-resolution powder neutron diffraction data indicates that the structure of CoGe1.5Te1.5 retains the a+a+a+ tilt system of the ideal skutterudite structure, while the anions are ordered in layers perpendicular to the [111] direction of the skutterudite unit cell. This anion ordering results in a lowering of the symmetry from cubic to rhombohedral (space group , a=12.3270(5) and c=15.102(1) Å at 293 K). The electrical transport properties have been investigated using four-probe resistivity and Seebeck coefficient measurements. The temperature dependence of the electrical resistivity and the magnitude of the Seebeck coefficient indicate that CoGe1.5Te1.5 is an n-type semiconductor.  相似文献   

4.
在碱式碳酸镍为主的盐溶液中用电沉积法制备出含Mo原子分数为18.68%的Ni-Mo合金镀层. X射线衍射(XRD)表明该镀层为非晶/纳米晶混合结构; 用差示扫描量热法(DSC)对这种非晶/纳米晶混合结构的合金进行了晶化动力学研究, 测得其晶化激活能(E)为3.84×105 kJ·mol-1; 晶化开始温度约为440 ℃, 与非晶态结构Ni-Mo合金镀层相比, 晶化温度提高了约13 ℃. 热处理过程发现, 非晶/纳米晶混合结构镀层中少量纳米晶的存在阻止了非晶态相转变的可能性, 提高了混合结构镀层的热稳定性和晶化温度; 镀层在450 ℃热处理过程中有新相产生, 其不仅提高了镀层的密实度, 同时也阻止了非晶态相的转变, 提高了镀层的热稳定性.  相似文献   

5.
A fast, facile and cost-effective method is used to synthesize Ni6MnO8 electrode with high electrochemical performance. The supercapacitor based on Ni6MnO8 electrode exhibits excellent stability, high area specific capacitance and promising energy and power density.  相似文献   

6.
The title compounds were prepared from the elements in the stoichiometric ratio at 800 °C under exclusion of air. Tl6Si2Te6 crystallizes in the space group P1¯, isostructural with Tl6Ge2Te6, with , , , α=89.158(2)°, β=96.544(2)°, γ=100.685(2)°, (Z=2). Its structure is composed of dimeric [Si2Te6]6− units with a Si-Si single bond, while the Tl atoms are irregularly coordinated by five to six Te atoms. Numerous weakly bonding Tl-Tl contacts exist. Both title compounds are black semiconductors with small band gaps, calculated to be 0.9 eV for Tl6Si2Te6 and 0.5 eV for Tl6Ge2Te6. The Seebeck coefficients are +65 μV K−1 in case of Tl6Si2Te6 and +150 μV K−1 in case of Tl6Ge2Te6 at 300 K, and the electrical conductivities are 5.5 and 3 Ω−1 cm−1, respectively.  相似文献   

7.
The structure of La6Mo8O33 has been determined from a triple pattern powder diffraction analysis. Two high-resolution neutron diffraction patterns collected at 1.594 and 2.398 Å and one X-rays were used. This molybdate crystallizes in a non-centrosymmetric monoclinic space group P21(N°4), Z=2,a=10.7411(3) Å, b=11.9678(3) Å, c=11.7722(3) Å, β=116.062 (1)°. La6Mo8O33 is an unusual ordered defect Scheelite. Hence, it should be described with cation vacancies and an extra oxygen atom following the formula: La62Mo8O32+1. This extra oxygen atom leads to a pyramidal environment, whereas the other molybdenum atoms present tetrahedral environment. A molybdenum tetrahedral is connecting to the pyramid, forming an [Mo2O9] unit.  相似文献   

8.
Single crystals of the new borides Ni12AlB8, and Ni10.6Ga0.4B6 were synthesized from the elements and characterized by XRD and EDXS measurements. The crystal structures were refined on the basis of single crystal data. Ni12AlB8 (oC252, Cmce, a=10.527(2), b=14.527(2), c=14.554(2) Å, Z=12, 1350 reflections, 127 parameters, R1(F)=0.0284, wR2(F2)=0.0590) represents a new structure type with isolated B atoms and B5 fragments of a B-B zig-zag chain. Because the pseudotetragonal metric crystals are usually twinned. Ni10.6Ga0.4B6 (oP68, Pnma, a=12.305(2), b=2.9488(6), c=16.914(3) Å, Z=4, 1386 reflections, 86 parameters, R1(F)=0.0394, wR2(F2)=0.104) is closely related to binary Ni borides. The structure contains B-B zig-zag chains and isolated B atoms. Ni12GaB8 is isotypical to the Al-compound (a=10.569(4), b=14.527(4) and c=14.557(5) Å).  相似文献   

9.
We present a new series of ternary chalcogenides, derived from divalent molybdenum: M2Mo6X6. These compounds crystallize in a hexagonal lattice with a ≈ 9 Å, c ≈ 4.5 Å, and space group P63m. The compounds are characterized by clusters (Mo3)1 in the form of linear chains, resulting from a linear condensation of Mo6 octahedral clusters. The (Mo3)1 clusters are well separated from each other, with the shortest MoMo intercluster distance larger than 6 Å. The resulting pseudo-one-dimensional structures show remarkable anisotropy of physical properties.  相似文献   

10.
Three new tellurites, LaTeNbO6 and La4Te6M2O23 (M=Nb or Ta) have been synthesized, as bulk phase powders and crystals, by using La2O3, Nb2O5 (or Ta2O5), and TeO2 as reagents. The structures of LaTeNbO6 and La4Te6Ta2O23 were determined by single crystal X-ray diffraction. LaTeNbO6 consists of one-dimensional corner-linked chains of NbO6 octahedra that are connected by TeO3 polyhedra. La4Te6M2O23 (M=Nb or Ta) is composed of corner-linked chains of MO6 octahedra that are also connected by TeO4 and two TeO3 polyhedra. In all of the reported materials, Te4+ is in an asymmetric coordination environment attributable to its stereo-active lone-pair. Infrared, thermogravimetric, and dielectric analyses are also presented. Crystallographic information: LaTeNbO6, triclinic, space group P−1, a=6.7842(6) Å, b=7.4473(6) Å, c=10.7519(9) Å, α=79.6490(10)°, β=76.920(2)°, γ=89.923(2)°, Z=4; La4Te6Ta2O23, monoclinic, space group C2/c, a=23.4676(17) Å, b=12.1291(9) Å, c=7.6416(6) Å, β=101.2580(10)°, Z=4.  相似文献   

11.
Mg二次电池正极材料Cu2Mo6S8的合成与表征   总被引:1,自引:0,他引:1  
采用CuS.H2O、MoS2、Mo为原料,用熔盐法(KCl为熔盐)合成了谢弗雷尔相的Cu2Mo6S8正极材料,并用XRD,SEM,循环伏安测试,充放电测试对材料的结构和电化学性能进行研究。XRD结果表明本Cu2Mo6S8正极材料属于R3空间群,具有良好的晶型。电化学测试表明,当材料在电压0.2~2 V范围内进行充放电时,其放电比容量在90 mAh.g-1左右,循环稳定性和可逆性均良好。该材料的充放电曲线中在1.2 V和1.9 V分别有还原峰,0.7 V和1.0 V分别有氧化峰,与伏安曲线相对应。  相似文献   

12.
Crystals of Ln5Mo2O12 (Ln = Y, Gd) were grown by electrochemical reduction of alkali-molybdate/rare-earth oxide melts at 1075–1100°C. A single crystal of Y5Mo2O12, used for structure determination, was found to be monoclinic with a = 12.2376(7) Å, b = 5.7177(8) Å, c = 7.4835(5) Å, β = 108.034(5)°, and Z = 2. Although the structure was refined in space group C2/m, the true space group appears to be P21/m. In Y5Mo2O12, rutile-like sheets of edge-shared MoO6 chains linked by YO6 octahedra are interconnected with YO7 monocapped trigonal prisms. The Mo atoms in the chains have alternating distances of 2.496 and 3.221 Å and in that respect are similar to MoO2. However, in contrast to metallic MoO2 both the Y and Gd compounds are n-type semiconductors with room temperature resistivities of the order of 103 ohm-cm. Magnetic susceptibility measurements confirm the presence of one unpaired electron per Mo2 unit. The semiconducting behavior can be explained in terms of an unfavorable bridging oxygen coordination which prevents electron delocalization through metal-oxygen pi bonding as in MoO2.  相似文献   

13.
The new Chevrel phase Ti0.3Mo5RuSe8 has been synthesized and characterized by quantitative microprobe analysis, powder X-ray diffraction, and high-temperature thermoelectric properties measurements. The thermoelectric properties of this compound are compared to the previously reported data for other related Chevrel phases. We report also the results of Rietveld analysis of powder X-ray diffraction data for Ti0.3Mo5RuSe8. This compound adopts the rhombohedral Chevrel phase structure (space group , Z=3) with hexagonal lattice constants a=9.75430(25) Å and c=10.79064(40) Å. The low level of incorporation and low scattering power of Ti precluded the identification of the Ti positions, and Rietveld refinement was carried out only for the Mo5RuSe8 framework of Ti0.3Mo5RuSe8 (Rp=10.5%, Rwp=14.6%). Rietveld analysis was also used to refine the structure of the unfilled phase Mo5RuSe8 (, Z=3, a=9.63994(8) Å, c=10.97191(11) Å, Rp=8.0%, Rwp=10.5%). Comparisons between the two structures are made.  相似文献   

14.
An intial-state molecular-orbital study of NiO (bunsenite) with cluster models produces lattice and force constants close to bulk values and permits assignment of photoemission and optical charge-transfer absorption bands. It is stressed that shake-up effects complicating electronic spectra are unrelated to mechanical properties and structures.  相似文献   

15.
Single crystals of CsHo3Te5 and Cs3Tm11Te18 have been grown as byproducts in the synthesis of CsLnZnTe3 (Ln=Ho or Tm) through the reaction of Ln, Zn, and Te with a CsCl flux at 850 °C. The crystal structures have been determined from single-crystal X-ray diffraction data. CsHo3Te5 crystallizes in space group Pnma of the orthorhombic system whereas Cs3Tm11Te18 crystallizes in the space group C2/m of the monoclinic system. Each of the compounds adopts a three-dimensional structure; each possesses tunnels built from LnTe6 octahedra that are filled with Cs atoms. The pseudo-rectangular tunnel in CsHo3Te5 is large enough in cross-section to accommodate two symmetrically equivalent Cs atoms. In the Cs3Tm11Te18 structure there are two different sized tunnels: the smaller one is only large enough to host one Cs atom per unit cell whereas the larger one can accommodate two Cs atoms. The electronic structure of CsHo3Te5 was calculated. The band gap is estimated to be about 1.2 eV, consistent with the black color of the crystals.  相似文献   

16.
Four probe electrical resistivity measurements between 1.5 and 300 K were made on single crystals of the violet-red bronze Na0.9Mo6O17 grown by a temperature gradient flux technique. The temperature variation of the resistivity shows metallic conductivity and highly anisotropic behavior similar to K0.9Mo6O17 and Li0.9Mo6O17. The room-temperature resistivity, measured in the direction parallel to the plate axis, is 3.0 × 10?3 Ω cm and perpendicular to that axis it is 0.21 Ω cm. A transition observed at ~88 K is possibly related to the onset of a charge density wave. The temperature variation of the susceptibility show Pauli paramagnetic behavior at high temperature, and highly anomalous behavior in the vicinity of the transition at low temperatures.  相似文献   

17.
The crystals of Ni0,33Mo3Se4, are triclinic, space group P1, with two formula units in a cell: a = 6,727 (9) Å, b = 6,582 (11) Å, c = 6,751 (6) Å, α = 90.61° (10), β = 92.17° (10), γ = 90.98° (12.) The structure was solved by analogy with Mo3Se4 and refined by a full-matrix least squares program to R = 0,093 for 822 independent reflexions. The channels present in Mo3Se4 are occupied by Ni so that Ni0,33Mo3Se4 is always a metallic compound.  相似文献   

18.
Sintering conditions of Cu4Mo6S8 pellets, 20 mm in diameter and about 4 mm thick have been determined. The expulsion of copper out of the pellet for an annealing temperature of 1100 ° C has been observed, in agreement with the evolution of the phase diagram when the temperature increases. The appearance of Cu2S cristallites on the surface of the films deposited from highly densified targets associated with a high excess of copper and sulfur can be correlated with the behavior observed on the pellets. In fact the increase of the temperature of the target under the laser beam impact is likely responsible for a copper migration on its surface, which leads to the observed composition of the film.  相似文献   

19.
The Ginzburg number of superconducting Chevrel phases MxMo6S8 with small coherence length (10−3 to 10−5) is intermediate between those obtained for conventional low Tc materials (10−8) and those of high Tc (10−1) indicating that these phases may display features in the dynamics of the vortices similar to those observed in high Tc superconductors. In this work we present a detailed study of I–V measurements close to the Bc2 line carried out on quasi epitaxial thin films of Cu2Mo6S8. The non-linear I–V curves show a scaling behaviour making possible to determine a transition temperature between an unpinned vortex state and a vortex glass state. However, the temperature range of the unpinned vortex state is much wider than expected.  相似文献   

20.
 Single crystals of K2Ag12Te7 (a = 11.460(2), c = 4.660(1) ?; V = 530.01 ?3; space group: P63/m; Z = 1) were synthesized under hydrothermal conditions at 250°C in concentrated aqueous KOH solution from elementary silver and tellurium. The crystal structure is characterized by trigonal prismatic KTe6 polyhedra, connected via two common faces to KTe3 rods parallel to [001]. These rods are combined by two crystallographically independent Ag atoms, each coordinated to four Te and three Ag atoms (Ag–Te and Ag–Ag < 3.1 ?) to a framework of the formula (K2Ag12Te6)2 +  and with channels parallel to the sixfold axis. These channels are statistically occupied by one further Te atom per unit cell, distributed over two independent positions.  相似文献   

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