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1.
The present work was aimed on utilizing the solid state microwave synthetic method for the growth of molybdenum disulphide (MoS2) and tungsten disulphide (WS2) in powder as well as in the form of thin films. It was observed that the microwave exposure of simple powder mixture of Mo (or W) and S could not lead to the formation of MoS2 (or WS2).Therefore the work was pursued by the study of the possibility to use this technique to grow thin films. Either Mo or W in the form of thin foils or Mo layers deposited by sputtering onto glass substrates was used as metal source. These metal samples were introduced with some sulphur into a Pyrex tube and sealed under vacuum. After microwave oven exposure the formation of polycrystalline 2H-WS2 with well-defined grains was confirmed by X-ray diffraction and scanning electron microscopy, respectively. Mo foil as well as Mo layers deposited on glass showed formation of MoS2 under the limit of our experimental conditions that is to say homogeneous thin films can be achieved only as small surface films.  相似文献   

2.
Nanoporous titanium dioxide (TiO2) based conductometric sensors have been fabricated and their sensitivity to hydrogen (H2) gas has been investigated. A filtered cathodic vacuum arc (FCVA) system was used to deposit ultra-smooth Ti thin films on a transducer having patterned inter-digital gold electrodes (IDTs). Nanoporous TiO2 films were obtained by anodization of the titanium (Ti) thin films using a neutral 0.5% (wt) NH4F in ethylene glycol solution at 5 V for 1 h. After anodization, the films were annealed at 600 °C for 8 h to convert the remaining Ti into TiO2. The scanning electron microscopy (SEM) images revealed that the average diameters of the nanopores are in the range of 20 to 25 nm. The sensor was exposed to different concentrations of H2 in synthetic air at operating temperatures between 100 °C and 300 °C. The sensor responded with a highest sensitivity of 1.24 to 1% of H2 gas at 225 °C.  相似文献   

3.
The glass transition temperatures of (1?x)Na2O·12xMO2·2SiO2 and Na2xMO2·(2 ?x)SiO2 glasses, with M = Ti or Zr, have been related to the structural role and coordination of Ti and Zr. The role of network-former, intermediate or modifier of a cation has been fundamentally linked to ionic field strength; Tg values depend on ionic field strength and coordination. Titanium behaves like an intermediate oxide; its coordination ranges between four and six, depending on TiSi ratio. The role of zirconium changes according to the degree of substitution for Na or Si and progressively approaches that of a modifier ion.  相似文献   

4.
Glass-ceramic matrices containing zirconolite (nominally Ca(Zr,Hf)Ti2O7) crystals in their bulk that would incorporate high proportions of minor actinides (Np, Am, Cm) or plutonium could be envisaged for their immobilization. Zirconolite-based glass-ceramics can be prepared by controlled crystallization of zirconolite in glasses belonging to SiO2–Al2O3–CaO–Na2O–TiO2–ZrO2–HfO2 system. In this study, neodymium was used as trivalent actinides surrogate. Increasing Al2O3 concentration in glass composition had a strong effect on the nucleation rate I z of zirconolite crystals in the bulk, on the amount of neodymium incorporated in zirconolite phase and on the crystal growth rate of silicate phases (titanite + anorthite) from glass surface. These results could be explained by the existence of competition—in favor of aluminum—between Al3+ and (Ti4+, Zr4+, Hf4+) ions for their association with charge compensators cations to facilitate their incorporation in the glassy network. Differential thermal analysis (DTA) was used to study exothermal effects associated with bulk and surface crystallization. 27Al magic angle spinning nuclear magnetic resonance (MAS NMR) spectra showed that aluminum enters glasses network predominantly in 4-fold coordination. Neodymium optical absorption and fluorescence spectroscopies showed that the Al2O3 concentration changes performed in this study had not significant effect on Nd3+ ions environment in glasses.  相似文献   

5.
The effects of Co, Fe, Mn, and Ti oxide additions on the sinterability and crystal-chemical, thermal, and electrical properties of Ce0.8Gd0.2O2−δ have been studied. The results indicate that these oxides enhance the sinterability of the mixed oxide, regardless of whether they were introduced before or after synthesis. The most effective sintering aid is Co2O3. The lattice parameters of Ce0.8Gd0.2O2−δ samples containing different metal oxide additions (1 mol %) are refined in space group Fm3m. The temperature-dependent thermal expansion data are used to determine the linear thermal expansion coefficients of the samples. Manganese oxide additions reduce the electrical conductivity of Ce0.8Gd0.2O2−δ, whereas the other dopants increase it in the order Ti < Fe < Co. The activation energy for conduction increases in the order Co < Ti < Fe < Mn. Original Russian Text ? E.Yu. Pikalova, A.N. Demina, A.K. Demin, A.A. Murashkina, V.E. Sopemikov, N.O. Esina, 2007, published in Neorganicheskie Material, 2007, Vol. 43, No. 7, pp. 830–837.  相似文献   

6.
New superconducting ternary silicides LaRhSi3 and LaIrSi3 have been prepared by arc melting from the elements and annealing for ten days at 900°C. A single crystal study shows these materials to be of tetragonal symmetry and isostructural with BaPtSn3. Their superconducting transition temperature which depends strongly on stoichiometry and thermal treatment occurs between 1.9 K and 2.7 K. The structures have been compared to those of the superconducting compounds LaRh2Si2 and La2Rh3Si5. The occurence of superconductivity in these materials seems to be related to the presence of similar coordination polyhedra for Rh or Ir and Si atoms.  相似文献   

7.
We systematize available experimental data on the crystal structure of the ternary halides K2(Rb2,Cs2,Tl2)TeBr6(I6) and Rb3(Cs3)Sb2(Bi2)Br9(I9), analyze the general trends in the properties of their single crystals, and examine the key features of the physicochemical interaction in related systems.  相似文献   

8.
Quenchable, homogenous high pressure phases in the systems AgSbSe2 - AgInSe2 and AgBiSe2 - AgInSe2 could be synthesized from appropriate mixtures of the ternary compounds in a belt-type high-pressure apparatus. The phases AgSb1?xInxSe2 crystallize with the rocksalt structure at the Sb-rich side and with the α-NaFeO2 structure at the In-rich side of the phase diagram. All AgBi1?xInxSe2 samples have α-NaFeO2-structure. The high temperature B1-type modification of AgBiSe2 is quenchable to room temperature at high pressures. Annealing of the high pressure phases at 1 bar and 300°C yielded the starting mixtures of AgInSe2 with chalcopyrite structure and AgSbSe2 or AgBiSe2, rsp. At 1 bar, 25°C the high pressure phases could be stored for at least 8 months.  相似文献   

9.
An extensive theoretical study is performed for wide bandgap crystalline oxides and nitrides, namely, SiO2, GeO2, Al2O3, Si3N4, and Ge3N4. Their important polymorphs are considered which are for SiO2: α-quartz, α- and β-cristobalite and stishovite, for GeO2: α-quartz, and rutile, for Al2O3: α-phase, for Si3N4 and Ge3N4: α- and β-phases. This work constitutes a comprehensive account of both electronic structure and the elastic properties of these important insulating oxides and nitrides obtained with high accuracy based on density functional theory within the local density approximation. Two different norm-conserving ab initio pseudopotentials have been tested which agree in all respects with the only exception arising for the elastic properties of rutile GeO2. The agreement with experimental values, when available, are seen to be highly satisfactory. The uniformity and the well convergence of this approach enables an unbiased assessment of important physical parameters within each material and among different insulating oxide and nitrides. The computed static electric susceptibilities are observed to display a strong correlation with their mass densities. There is a marked discrepancy between the considered oxides and nitrides with the latter having sudden increase of density of states away from the respective band edges. This is expected to give rise to excessive carrier scattering which can practically preclude bulk impact ionization process in Si3N4 and Ge3N4.  相似文献   

10.
Crystallization in the systems La2(CO3)3 ⋅ 6H2O-CaCO3(BaCO3)-R-H2O (R = Na2CO3, K2CO3, NaHCO3, KHCO3, NaCl, NH4Cl, CO(NH2)2) was studied under hydrothermal conditions (400–450°C). The solid reaction products were found to contain LaOHCO3 and NaLa(CO3)2. Detailed thermal decomposition schemes were proposed for these phases, and their lattice parameters were refined. __________ Translated from Neorganicheskie Materialy, Vol. 41, No. 11, 2005, pp. 1366–1372. Original Russian Text Copyright ? 2005 by Nikol'skaya, Dem'yanets.  相似文献   

11.
Sol-gel SiO2/TiO2 and TiO2/SiO2 bi-layer films have been deposited from a polymeric SiO2 solution and either a polymeric TiO2 mother solution (MS) or a derived TiO2 crystalline suspension (CS). The chemical and structural properties of MS and CS bi-layer films heat-treated at 500 °C have been investigated by Fourier transform infrared spectroscopy, X-ray photoelectron spectroscopy, and transmission electron microscospy. Water contact angle measurements show that MS SiO2/TiO2 and CS TiO2/SiO2 bi-layer films exhibit a natural superhydrophilicity, but cannot maintain a zero contact angle for a long time over film aging. In contrast, CS SiO2/TiO2 bi-layer films exhibit a natural, persistent, and regenerable superhydrophilicity without the need of UV light. Superhydrophilic properties of bi-layer films are discussed with respect to the nature of the TiO2 single-layer component and arrangement of the bi-layer structure, i.e. TiO2 underlayer or overlayer.  相似文献   

12.
Na2O-GeO2 glasses containing 25~35 mole% Na2O can be crystallized to give a new sodium germanate crystal together with Na4Ge9O20, Na2GeO3 and/or Na2Ge4O9 crystals. The new crystal is obtained as a principal crystallization product from the glass containing 33.3 mole% Na2O, and is given a composition of Na2Ge2O5. This sodium digermanate crystal is monoclinic with lattice parameters; a0 = 8.421, b0 = 4.962, c0 = 12.67 Å and β = 103.5°, and isostructural with β-Na2Si2O5. It is shown that the crystal is thermodynamically metastable.  相似文献   

13.
Aiming for the investigation of insulating properties of aluminum oxide (Al2O3) layers, as well as the combination of this oxide with tin dioxide (SnO2) for application in transparent field effect transistors, Al thin films are deposited by resistive evaporation on top of SnO2 thin films deposited by sol–gel dip-coating process. The oxidation of Al films to Al2O3 are carried out by thermal annealing at 500 °C in room conditions or oxygen atmosphere. X-ray diffraction data indicate that tetragonal Al2O3 is indeed obtained. A simple device and electric circuit is proposed to measure the insulating properties of aluminum oxide and the transport properties of SnO2 as well. Results indicate a fair insulation when four layers or Al2O3 are grown on the tin dioxide film, concomitant with thermal annealing between each layer. The current magnitude through the insulating layer is only 0.2% of the current through the semiconductor film, even though the conductivity of the SnO2 alone is not very high (the average resistivity is 2 Ω cm), because no doping is used. The presented results are a good indication that this combination may be useful for transparent devices.  相似文献   

14.
采用水/溶剂热法合成了铜的亚微米级有机金属框架Cu_3(BTC)_2,并用扫描电镜、透射电镜、X射线粉末衍射、傅里叶红外光谱仪及光电子能谱仪对材料的形貌结构及表面性质进行了分析。将制备的Cu_3(BTC)_2用于吸附去除水中亚甲基蓝(MB)污染物。吸附结果表明,MB在Cu_3(BTC)_2上的吸附符合Freundlich模型。当MB初始浓度为30mg/L时,平衡吸附量为29.5mg/g,当初始浓度提高到300mg/L时,平衡吸附量达到244.3mg/g,吸附效果优于文献中报道的大部分吸附材料。  相似文献   

15.
In order to conciliate dielectric and non-Ohmic properties of CaCu3Ti4O12 (CCTO) ceramics, NiO, SnO2, SiO2, and Al2O3 were added as sintering aids to promote the grain growth of CCTO ceramics. Microstructure, dielectric properties, and non-Ohmic behavior of the CCTO ceramics were investigated. Among them, NiO-modified CCTO exhibits good dielectric and non-Ohmic properties (ε = 69833, tanδ = 0.073, α = 3.66 and E B = 296.7 V/cm), due to NiO is also one of giant dielectric materials. Therefore, it is suitable for applying semiconductor circuits. The relationship between electrical current density (J) and electrical field (E) demonstrated that Schottky barrier should exist at grain boundaries. Non-linear coefficient α was directly proportional to the height of barrier. Depressing barrier width would improve significantly dielectric permittivity but decrease breakdown voltage.  相似文献   

16.
Nanophase alpha-alumina and hydroxyapatite composites (with and without 5 wt% AlF3, CaF2 or MgF2, added separately) were hot pressed at 1100 °C and 1200 °C to investigate their mechanical properties and phase stability. Hydroxyapatite slightly decomposed to tri-calcium-phosphate when there was no F present. With the addition of AlF3, CaF2 or MgF2 into the composite, it improved its thermal stability and mechanical properties. Substitution of OH by F ions in hydroxyapatite was verified by the change in hydroxyapatite's hexagonal lattice parameters and unit cell volume. A fracture toughness of 2.8 MPa  and μ-hardness of 8.25 GPa were calculated for the composite containing CaF2 after the hot pressing at 1200 °C.  相似文献   

17.
First-principles cluster calculations are reported of the local electronic structure of the three compounds: La2CuO4, Sr2CuO2Cl2, and Sr2CuO2F2. The copper and the planar oxygen 2p atomic orbitals exhibit a similar degree of covalency. The out-of-plane orbitals, however, are quite different with the atomic orbital lowered significantly in energy for chlorine and fluorine apical positions.  相似文献   

18.
Glass-ceramics containing (Hf,Zr)-zirconolite crystals (nominally CaHf1−x Zr x Ti2O7 with 0 ≤ x ≤ 1) were envisaged to immobilize minor actinides and plutonium. Such materials were prepared in this study by controlled crystallization of glasses belonging to the SiO2–Al2O3–CaO–Na2O–TiO2–HfO2–ZrO2–Nd2O3 system. Neodymium was used as trivalent actinides surrogate. The effect of total or partial substitution of ZrO2 by HfO2 (neutron poison for fission reactions) on glass crystallization in the bulk and near the surface is presented. It appeared that Hf/Zr substitution had not significant effect on nature, structure, and composition of crystals formed both on glass surface (titanite + anorthite) and in the bulk (zirconolite). This result can be explained by the close properties of Zr4+ and Hf4+ ions and by their similar structural role in glass structure. However, strong differences were observed between the nucleation rate IZ of zirconolite crystals in glasses containing only HfO2 and in glasses containing only ZrO2. Hf-zirconolite (CaHfTi2O7) crystals were shown to nucleate only very slowly in comparison with Zr-zirconolite (CaZrTi2O7) crystals. Composition changes - by increasing either HfO2 or Al2O3 concentration or by introducing ZrO2 in parent glass - were performed to increase IZ in hafnium-rich glasses. The proportion of Nd3+ ions incorporated in the zirconolite phase was estimated using ESR.  相似文献   

19.
Powders with nominal composition (Tl,Cr0.15)Sr2(Ca0.9,Pr0.1)Cu2O7 (Tl-1212) and Tc90 K were used to fabricate Ag-sheathed superconducting tapes employing the powder-in-tube (PIT) method. The tapes were subjected to intermediate mechanical rolling or pressing. Conditions that enhance the transport critical current density (Jc) of the tapes were investigated. Optimum annealing temperature and period together with uniaxial pressing are necessary to increase Jc of the Tl-1212/Ag tapes. Annealing at 910 °C for 0.5–1 h enhanced the 1212 phase formation and improved intergranular connectivity between grains, as well as to provide healing for the fractured structure caused by deformation process. A relatively longer annealing time at higher temperature gave rise to secondary phases and resulted in the decrease of Jc. Mechanical uniaxial pressing greatly densified the tapes core and thus led to closer contact between grains. At liquid nitrogen temperature and zero field, Jc of the pressed tapes annealed at 910 °C for 1 h is 3060±127 A cm−2. The initial drastic drop of Jc in low fields (<0.06 T) indicates the performance of the tapes is limited by weak links. No significant anisotropic transport properties were observed in applied magnetic field. This is due to the absence of texturing in the tapes as the grains are randomly oriented revealed through SEM micrographs.  相似文献   

20.
Yong Liu 《Materials Letters》2009,63(28):2526-2528
Magnetic monodisperse ferrite MFe2O4 (M = Fe, Co, Ni) nanoparticles have been successfully deposited on carbon nanotubes (CNTs) by in situ high-temperature hydrolysis and inorganic polymerization of metal salts and CNTs in polyol solution. X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), energy-dispersive X-ray spectrometry (EDS) and vibrating sample magnetometer (VSM) investigations were used to characterize the final products. The influencing factors for formation of CoFe2O4 nanoparticles along CNTs have also been discussed briefly. The main advantage of this synthetic strategy is that it is beneficial for the fabrication of magnetic CNTs with a compact layer of nanoparticles and could be extended to prepare series of ferrite/CNTs nanocomposites via the substitution of metal cations.  相似文献   

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