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1.
A Fluidized Bed Metal–Organic Chemical Vapor Deposition (FB-MOCVD) process was developed for the growth of tin oxide thin films on large hollow Ni particles. Tetraethyl tin was used as tin source and dry air both as fluidization gas and oxidant reagent. The SnO 2 films were grown in a FBCVD reactor under reduced pressure (13.3 kPa) in the temperature range of 633–663 K. A series of specific experiments was carried out to optimize the design of the reactor and to determine the range of experimental parameters (flow rate, pressure, temperature) leading to good fluidization of the large hollow Ni particles used as base material. The SnO 2 films deposited on particles exhibited a dense nodular surface morphology similar to that previously observed on flat substrates. The relative thickness of the films was determined by EDS analyses and the real values were measured by SEM on cross-sections of particles. The SnO 2 films exhibit satisfactory thickness uniformity from one particle to another in the same batch and from run to run. XRD studies revealed that the films exhibited good crystallinity with the cassiterite structure. Traces of NiO were found at the SnO 2/Ni interface. Finally, the SnO 2 CVD coated-Ni particles were used as anodes in an electrochemical cell. The potential limit of oxygen evolution measured was that of the SnO 2 layer despite the initial porosity of the hollow Ni particles inherent to their preparation. This work is the first step towards the preparation of high specific surface area electrodes. 相似文献
2.
Well-crystallized SrMoO 4 films have been prepared directly on molybdenum substrates in an alkaline aqueous solution containing strontium ions by a simple chemical reaction at room temperature. In order to keep the free growth of SrMoO 4 crystals in solutions, a mild oxidizing agent, NaClO, plays an important role in the formation of desired film. XRD and SEM results indicate that the films have single phase and uniform surfaces. The film shows a broad emission band centered at 487 nm with the excitation light of 240 nm, 250 nm and 270 nm at room temperature, respectively. 相似文献
3.
We studied the Fermi surface of the organic conductor (TMTSF) 2NO 3 through the measurements of magnetic quantum oscillations. Well defined Shuvnikov-de Haas(SdH) oscillations with frequency of ca. 60T can be observed below 8K and above 6T at the ambient pressure. Under a pressure of 8kbar, different oscillations with frequency of ca. 180T is observed above 10T at 450mK. Electron structure at low temperature seems strongly modified upon application of pressure which may explain the absence of superconductivity and the field-induced spin-density waves. The angular magnetoresistance could not be fit neither by Yamaji's model nor by Lebed's. 相似文献
4.
PolycrystaUine SnO2 thin films were deposited on sapphire substrates at 450℃ under different ambient oxygen pressures by pulsed laser deposition technique. The effect of ambient oxygen pressure on the structural, optical and electrical properties of SnO2 thin films was studied. X-my diffraction and Hall measurements show that increasing the ambient oxygen pressure can improve crystallization of the films and decrease resistivity of the films. A violet emission peak centered at 409 nm was observed from photoluminescence measurements for SnO2 films under deposition ambient oxygen pressure above 5 Pa, which is related to the improvement of crystalline of the films. 相似文献
5.
Cu(In,Ga)Se 2 thin films were prepared from aqueous solution by pulse electrodeposition. It was found that the co-deposition of the species occurred under a 3D growth with instantaneous nucleation. The morphology of the pulse-electrodeposited film can be improved by adjusting the duty cycle. The significant loss of indium and reduction of In-Se compound(s) accordingly were observed with decrease of duty cycle. Chalcopyrite structure Cu(In,Ga)Se 2 films with p-type behavior and enhancement in crystallinity were obtained after annealing treatment in Ar atmosphere. 相似文献
6.
The mechanical and thermal properties of single crystal Tb 2(MoO 4) 3 have been systematically studied. The result of microhardness measurement indicates that the crystal belongs to the soft materials category. The thermodynamic parameters obtained from DTA analysis were used for determining the type of liquid-solid interface during crystal growth. Negative thermal expansion along the c-axis was observed, and this behavior was attributed to the bent Tb-O-Mo bonds. The specific heat of the crystal was measured to be 0.122 cal g −1 K −1 at 293.15 K. The thermal conductivity of Tb 2(MoO 4) 3 at room temperature was found to be smaller than that of representative ferroelectric LiNbO 3. 相似文献
7.
The isothermal grain growth of SnO 2 thin films prepared by pulsed laser deposition techniques was investigated at Si (100) substrate temperatures between 300 and 450 °C with 50 °C intervals for different annealing times. X-ray diffraction patterns proved that the average grain sizes are in the range of 2.4–27.8 nm. The grain growth data were analyzed using two different models. The first model, assuming normal grain growth as that in conventional polycrystalline materials, yields large grain growth exponent ( n) and extremely low activation energy ( Q). Although it can describe the evolution of grain sizes, it fails to give satisfactory physical interpretation of n and Q, both beyond the theoretical predictions. The second model is based on the structural relaxation of the interface component in nanocrystalline materials. In this case, the ordering of distorted interfaces by structural relaxation proceeds with grain growth. This structure relaxation model not only describes the evolutions of grain growth well, but also makes reasonable attribution of the low activation energy to the short-range rearrangement of atoms in the interface region as well. 相似文献
8.
The crystallization conditions of Al 2(WO 4) 3 from Li 2O–WO 3 solvents (molar ratio 30.0:70.0, 32.5:67.5, 35.0:65.0, 45.0:55.0 and 55.0:45.0) as well as from Na 2O–WO 3 solvents (molar ratio 25.0:75.0, 27.5:72.5, 30.0:70.0 and 32.5:67.5) have been investigated. The concentration and temperature regions of crystallization of Al 2(WO 4) 3 and the density, viscosity as well as the solution losses due to evaporation have been established. On the basis of the data obtained it has been concluded that the most suitable solvent for growing Al 2(WO 4) 3 single crystals is Na 2O–WO 3 with a molar ratio of 27.5:72.5. 相似文献
9.
A major breaktrough in the developement of metal hydrides for hydrogen storage will require inexpensive intermetallic compounds that absorb large quantities of hydrogen at near ambient conditions (atmospheric pressure and room temperature). Unfortunately, in the last ten years there has been relatively little progress in this field. We investigated intermetallic compounds Ce(T 1−yAl y) 2 with T=Mn, Fe in the range 0.5≤ y<1.0. Mn, Fe and Al are inexpensive and Ce could be replaced by the low cost mischmetal (MM). The intermetallic compounds Ce(T, Al) 2 form the C14 and C15 Laves phases and they absorb hydrogen. A fraction of the totally absorbed hydrogen of about 2.5 H/(formula unit) forms a stable hydride (β-phase) at low pressures (<10 mbar). An additional H/(f.u.) is absorbed and reversibly desorbed at hydrogen pressures>10 mbar. The alloys and their hydriding characteristics were analyzed by means of X-ray diffraction and pressure-concentration isotherms. The two different absorption behaviours are correlated to the occupation of 96g-positions with different surrounding atomic constitutions. 相似文献
10.
Phase evolution and microwave dielectric properties of (1 − x)(Mg 0.95Co 0.05) 2TiO 4- xTiO 2 ( x = 0-1) ceramics prepared by the conventional mixed oxide route have been investigated. Increasing the TiO 2 content would lead to a main phase transformation from (Mg 0.95Co 0.05) 2TiO 4 to (Mg 0.95Co 0.05)TiO 3, (Mg 0.95Co 0.05)Ti 2O 5 and then TiO 2. Not only did the TiO 2 addition compensate the τf, it also lowered the sintering temperature of specimen. A huge drop of Q × f occurs at a 40-60 mol% TiO 2 addition was attributed to the formation of (Mg 0.95Co 0.05)Ti 2O 5 phase. Specimen with x = 0.78 can possess an excellent combination of microwave dielectric properties: ?r ∼ 24.77, Q × f ∼ 38,500 GHz and τf ∼ −1.3 ppm/°C. 相似文献
11.
The title compound was obtained during the crystal growth of two κ-type superconductors, κ-(BED-TTF) 2Cu(CN)[N(CN) 2] and κ′ -(BEDT-TTF) 2 Cu 2(CN) 3. This compound is a magnetic semiconductor, whose spin susceptibility is expressed by quadratic-layer Heisenberg antiferromagnet model (QLAF) between 32.6K and 220K. At 220K, a semiconductor-semiconductor transition into a high conductivity phase was observed by transport measurements. 相似文献
12.
SrBi 2(Ta 0.5Nb 0.5) 2O 9 (SBTN) thin films were obtained by polymeric precursor method on Pt/Ti/SiO 2/Si(1 0 0) substrates. The film is dense and crack-free after annealing at 700 °C for 2 h in static air. Crystallinity and morphological characteristic were examined by X-ray diffraction (XRD), field emission scanning electron microscopy (FEG-SEM) and atomic force microscopy (AFM). The films displayed rounded grains with a superficial roughness of 3.5 nm. The dielectric permittivity was 122 with loss tangent of 0.040. The remanent polarization ( Pr) and coercive field ( Ec) were 5.1 μC/cm 2 and 96 kV/cm, respectively. 相似文献
13.
K 3Lu(PO 4) 2:Ce single crystals have been studied under gamma, X-ray, VUV, and UV excitation. For all of the excitation forms, the luminescence of these materials is dominated by the d–f emission bands of Ce 3+. The shape and position of these bands, however, depends on the form of the excitation and on temperature due to crystallographic structural phase changes and multiple types of Lu 3+ ions sites in the which the Ce 3+ ion can substitute for Lu. The highly efficient and fast scintillation of these materials is based on radiative recombination of electron-hole pairs via Ce ions, and the scintillation characteristics identify K 3Lu(PO 4) 2:Ce as a promising fast and efficient scintillator. 相似文献
14.
The new phases KFe 2(SeO 2OH)(SeO 3) 3 and SrCo 2(SeO 2OH) 2(SeO 3) 2 have been synthesized under low-hydrothermal conditions and their structures were determined by single-crystal X-ray methods. Both compounds are monoclinic; KFe 2(SeO 2OH)(SeO 3) 3: space group P2, A = 9.983(4), B = 5.270(1), C = 10.614(4) Å, β = 97.42(2)°, V = 553.7 Å 3, Z = 2; SrCo 2(SeO 2OH) 2(SeO 3) 2: space group P2 ln, A = 14.984(2), B = 5.286(1), C = 13.790(2) Å, β = 94.72(1)°, V = 1088.5 Å 3 , Z = 4. The refinements converged to R-values of 2.9 and 3.6% respectively. The atomic arrangement in KFe2(SeO2OH)(SeO3)3 and SrCo2(SeO2OH)2(SeO3)2 is based on isolated MO6 octahedra (M = Fe3+, Co2+), which are corner-linked via trigonal pyramidal selenite groups to a framework structure. Interstitials are occupied by potassium or strontium atoms in ten- or eight-coordination respectively, and by the lone-pair electrons of the Se4+ atoms. Both compounds are not isotypic but are closely related and may be interpreted as different distortions of an idealized structure type in space group P2/m, which was modelled for a theoretical compound SrFe2(SeO3)4 by distance least squares refinement (program
). 相似文献
15.
Luminescence, luminescence excitation and electronic absorption spectra of europium salts of isomeric lutidine N-oxide derivatives were studied at 293 and 77 K. The role of radiative and non-radiative processes in emission intensity is discussed. The absorption transitions to the 3F J, 5D J, 5L J and 5G J levels and emissions from the 5D 0 and 5D 2 levels were detected. The role of CT transition inside the ligand and its influence on the LMCT transition is analysed. The co-ordinating function of the lutidine N-oxide group is discussed using IR spectroscopy. 相似文献
16.
A novel dibarium cadmium diborate, Ba 2Cd(BO 3) 2, has been successfully synthesized by standard solid-state reaction. Large sheet-like crystal with size up to 20 mm × 15 mm × 0.7 mm has been obtained using top-seed solution growth method. Ba 2Cd(BO 3) 2 crystallizes in the monoclinic space group C2/ m with a = 9.6305(4) Å, b = 5.3626(3) Å, c = 6.5236(2) Å, β = 118.079(3)°, Z = 2. The crystal structure is composed of isolated [BO 3] triangles, [CdO 6] octahedra and [BaO 9] polyhedra. CdO 6 are vertex-connected with six BO 3 to form infinite ∞[Cd(BO 3) 2] layers extending in (0 0 1) plane, and two rows of Ba atoms closely occupy two side of ∞[Cd(BO 3) 2] layers to forming stoichiometric sheets. IR and transmittance spectrum of Ba 2Cd(BO 3) 2 were reported. 相似文献
17.
Sb 5+-doped (NaBi) 0.38(LiCe) 0.05[] 0.14Bi 2Nb 2O 9 (represented as NBNLCS- x, where [] represents A-site vacancies) ceramics were prepared by the conventional solid-state route. The ceramics well sintered to approach ∼98.5% theoretical density and the tetragonality of crystal structure increased with Sb 5+ additions. However, the Curie temperature ( TC) and the piezoelectric coefficient ( d33) of Sb 5+-modified ceramics gradually decreased. The 3 mol% Sb 5+-doped samples exhibited optimum properties with a d33 value of ∼22 pC/N planar electromechanical coupling factor ( kp) of ∼11.2% and relatively high TC of ∼765 °C. These results indicate that NBNLCS- x material is a promising candidate for high-temperature piezoelectric applications. 相似文献
19.
Polycrystalline powder sample of KSr 4(BO 3) 3 was synthesized by high-temperature solid-state reaction. The influence of different rare earth dopants, i.e. Tb 3+, Tm 3+ and Ce 3+, on thermoluminescence (TL) of KSr 4(BO 3) 3 phosphor was discussed. The TL, photoluminescence (PL) and some dosimetric properties of Ce 3+-activated KSr 4(BO 3) 3 phosphor were studied. The effect of the concentration of Ce 3+ on TL intensity was investigated and the result showed that the optimum Ce 3+ concentration was 0.2 mol%. The TL kinetic parameters of KSr 4(BO 3) 3:0.002 Ce 3+ phosphor were calculated by computer glow curve deconvolution (CGCD) method. Characteristic emission peaking at about 407 and 383 nm due to the 4f 05d 1 → 2F (5/2, 7/2) transitions of Ce 3+ ion were observed both in PL and three-dimensional (3D) TL spectra. The dose–response of KSr 4(BO 3) 3:0.002 Ce 3+ to γ-ray was linear in the range from 1 to 1000 mGy. In addition, the decay of the TL intensity of KSr 4(BO 3) 3:0.002 Ce 3+ was also investigated. 相似文献
20.
Thermal expansion behavior of Th(MoO 4) 2, Na 2Th(MoO 4) 3 and Na 4Th(MoO 4) 4 was studied under vacuum in the temperature range of 298–1123 K by high temperature X-ray diffractometer. Th(MoO 4) 2 was synthesized by reacting ThO 2 with 2 mol of MoO 3, at 1073 K in air and Na 2Th(MoO 4) 3 and Na 4Th(MoO 4) 4 were prepared by reacting Th(MoO 4) 2 with 1 and 2 mol of Na 2MoO 4, respectively at 873 K in air. The XRD data of Th(MoO 4) 2 was indexed on orthorhombic system where as XRD data of Na 2Th(MoO 4) 3 and Na 4Th(MoO 4) 4 were indexed on tetragonal system. The lattice parameters and cell volume of all the three compounds, fit into polynomial expression with respect to temperature, showed positive thermal expansion (PTE) up to 1123 K. The average value of thermal expansion coefficients for Th(MoO 4) 2, Na 2Th(MoO 4) 3 and Na 4Th(MoO 4) 4 were determined from the high temperature data. 相似文献
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