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1.
The crystal structure of the ordered fluorite, Pr3RuO7, was refined from powder neutron diffraction data in Cmcm. An interesting structural feature is the presence of relatively well separated zig-zag chains of corner sharing RuO6 octahedra, Ru–Ru interchain distance 6.61 Å vs. Ru–Ru intrachain distance of 3.76 Å. Magnetic susceptibility data show a Curie–Weiss behavior for T>225 K with C=5.96(4) emu K mol−1 and θc=+11(2) K. In an attempt to separate the contributions of Pr(3+) and Ru(5+), the properties of isostructural Pr3TaO7 were also measured, yielding C=4.63(3) emu K mol−1. Thus, the contribution of Ru(5+), 4d3, S=3/2, to the measured Curie constant is estimated to be 1.33 emu K mol−1, not far from the spin-only value of 1.87 emu K mol−1. This supports the view that the Ru 4d electrons are localized and magnetic, not itinerant. A susceptibility maximum at about 50 K is attributed to long-range magnetic order and this is substantiated by neutron diffraction data. There is little evidence for one-dimensional antiferromagnetic correlations in this material but behavior characteristic of short-range ferromagnetic correlations attributed to Pr–Ru exchange interactions are found in the temperature range 50–200 K, consistent with the positive θc.  相似文献   

2.
《Materials Letters》2006,60(21-22):2611-2616
Cyclic voltammetry was used to investigate the electrochemical behaviors of Mg(II), Ce(III) and Co(II) in 3.00 mol L 1 urea–DMSO (dimethylsulfoxide). The electrode processes of Mg(II), Ce(III) and Co(II) reducing on Pt electrodes were irreversible steps. The transfer coefficient of Mg(II), Ce(III) and Co(II) in 3.00 mol L 1 urea–DMSO system was calculated as 0.07, 0.05 and 0.05 at 298.15 K, respectively. The diffusion coefficient of Mg(II), Ce(III) and Co(II) in 3.00 mol L 1 urea–DMSO system was calculated as 2.27 × 10 10, 1.77 × 10 10 and 3.16 × 10 10 m2 s 1 at 298.15 K, respectively. The MgCeCo alloy thin films with smooth, uniform and metallic luster were obtained on Cu substrates by cyclic electrodeposition in 0.01 mol L 1 Mg(ClO4)2–0.01 mol·L 1 Ce(CH3SO3)3−0.01 mol L 1 CoCl2–3.00 mol L 1 urea–DMSO system. The potential sweep rate was found to be important with respect to the adhesion of the thin films.  相似文献   

3.
Octadecasil, a clathrate-type inclusion compound, has been synthesized hydrothermally at 453 K with a gel having the composition 1.0SiO2:0.53tetramethylammonium (TMA+):0.54fluoride:86H2O. The crystal structure has been determined based on powder X-ray diffraction data taken at 298 K, and has been refined using Rietveld method. The result confirms the AST-type, all-silica framework model developed by Caullet et al. [P. Caullet, J.L. Guth, J. Hazm, J.M. Lamblin, H. Gies, Eur. J. Solid State Inorg. Chem. 28 (1991) 345]. Furthermore, by using a rigid body model the position and orientation of the occluded TMA+ cation in the rhombododecahedral [46612] cage can be determined; F anion has been located in the hexahedral [46] cage. The unit cell parameters, in the tetragonal space group I4/m, have been refined as: a = b = 9.07 Å, c = 13.44 Å, cell volume = 1104.97 Å3. The refined unit cell composition is |[N(CH3)4+]2.0F1.9|[Si20O40], i.e., both TMA+ and F ions possess near full occupancies, and compensate each other's electronic charges. The crystallization of the AST framework structure is the result of a cooperative structure-directing effect of both ions.  相似文献   

4.
The effect of neutron irradiation on a lithium tetraborate (Li2B4O7, LBO) single crystal has been investigated. The crystals of high optical quality are found to be quite stable under high neutron fluence. This study shows that LBO crystals can be used as a proportional counter for neutron fluxes of the order 109 cm−2 s−1 and higher. The detectors fabricated were found to have a sensitivity of ∼3×10−18 A (nv)−1.  相似文献   

5.
The low-cycle fatigue (LCF) properties and post-fatigue microstructure of a Fe–15Mn–10Cr–8Ni–4Si austenitic alloy were investigated under an axial strain control mode with total strain amplitudes, Δεt/2, ranging from 2.5 × 10−3 to 2 × 10−2. The fatigue resistance of the alloy was described by Coffin–Manson’s and Basquin’s relationships, and the corresponding fatigue parameters were evaluated. In addition, the Masing behavior, which is associated with a constant deformation mode during fatigue, was revealed at the examined strain amplitudes. Microstructural observations of the fatigue fractured samples showed that the strain induced ε-martensitic transformation accompanied by a planar slip of the Shockley partial dislocations in the austenite is the main deformation mode controlling the fatigue behavior of the studied alloy at Δεt/2 < 2 × 10−2. However, at Δεt/2 = 2 × 10−2, the formation of a cell structure was found in the austenite in addition to ε-martensitic transformation. The LCF resistance of the alloy was compared with conventional Cr–Ni austenitic stainless steels, ferrous base TRIP and TWIP steels and low yield point damping steels. It was found that at the studied strain amplitudes the alloy possessed a higher LCF resistance compared to conventional Fe-base alloys and steels. Remarkably, the fatigue ductility coefficient, εf′, of the studied alloy is 1.3–6 times higher than that of the stainless steels because of a cyclic deformation-induced ε-martensitic transformation. The results showed that the ε-martensitic transformation that occurred in the studied alloy during LCF is the main reason for the improved LCF resistance.  相似文献   

6.
Tm3+/Al3+ co-doped silica glass was prepared by sol–gel method combined with high temperature sintering. Glasses with compositions of xTm2O3–15xAl2O3–(100  16x) SiO2 (in mol%, x = 0.1, 0.3, 0.5, 0.8 and 1.0) were prepared. The high thulium doped silica glass was realized. Their spectroscopic parameters were calculated and analyzed by Judd–Ofelt theory. Large absorption cross section (4.65 × 10−21 cm2 at 1668 nm) and stimulated emission cross section (6.00 × 10−21 cm2 at 1812 nm), as well as low hydroxyl content (0.180 cm−1), long fluorescence lifetime (834 μs at 1800 nm), large σem × τrad (30.05 × 10−21 cm2 ms) and large relative intensity ratio of the 1.8 μm (3F4  3H6) to 1.46 (3H4  3F4) emissions (90.33) are achieved in this Tm3+/Al3+ co-doped silica glasses. According to emission characteristics, the optimum thulium doping concentration is around 0.8 mol%. The cross relaxation (CR) between ground and excited states of Tm3+ ions was used to explain the optimum thulium doping concentration. These results suggest that the sol–gel method is an effective way to prepare Tm3+ doped silica glass with high Tm3+ doping and prospective spectroscopic properties.  相似文献   

7.
《Materials Research Bulletin》2006,41(7):1392-1402
In situ high temperature X-ray diffraction (HTXRD) studies on monoclinic silicalite-1 (S-1, silica polymorph of ZSM-5) and an orthorhombic metallosilicate molecular sieve, zirconium silicalite-1 (ZrS-1) with MFI structure (Si/Zr = 50) have been carried out using a laboratory X-ray diffractometer with an Anton Parr HTK 1600 attachment. While the structure of the S-1 collapsed at 1123 K forming α-cristobalite. S-1 and ZrS-1 showed a complex thermal expansion behavior in the temperature range 298–1023 K, ZrS-1 was stable. Powder X-ray diffraction (PXRD) data taken in this region have shown strong negative lattice thermal expansion coefficient, αV = −6.75 × 10−6 and −17.92 × 10−6 K−1 in the temperature range 298–1023 K−1 for S-1 and ZrS-1 samples, respectively. The thermal expansion behavior of S-1 and ZrS-1 is anisotropic, with the relative strength of contraction along a axis is more than that along b and c axes. Three different thermal expansion regions could be identified in the overall temperature range (298–1023 K) studied, corroborating with the three steps of weight loss in the TG curve of ZrS-1 sample. While the region between 298 and 423 K, displays positive thermal expansion coefficient with αV = 2.647 × 10−6 and 4.24 × 10−6 K−1, the second region between 423 and 873 K shows strong negative thermal expansion (NTE) coefficient αV = −7.602 × 10−6 and −15.04 × 10−6 K−1, respectively, for S-1 and ZrS-1 samples. The region between 873 and 1023 K, shows a very strong NTE coefficient with αV = −12.08 × 10−6 and −45.622 × 10−6 K−1 for S-1 and ZrS-1, respectively, which is the highest in the whole temperature range studied. NTE seen over a temperature range 298–1023 K could be associated with transverse vibrations of bridging oxygen atoms in the structure which results in an apparent shortening of the Si–O distances.  相似文献   

8.
The Judd–Ofelt theory has been applied to analyze absorption spectra of Ho3+ ion in HoAl3(BO3)4 measured in spectral range 300–700 nm at room temperature. The Judd–Ofelt spectroscopic parameters have been determined as: Ω2 = 18.87 × 10−20 cm2, Ω4 = 17.04 × 10−20 cm2, Ω6 = 9.21 × 10−20 cm2. These parameters have been used to calculate radiative lifetimes and branching ratios of the luminescence manifolds. Three luminescent bands were found in the spectral range 450–700 nm ascribed to transitions from the 5F5, (5F4, 5S2) and 3K8 states to the ground state 5I8. Experimental intensities of these luminescence transitions were compared with those calculated by using Judd–Ofelt theory and the system of kinetic equations for populations of starting luminescing states. Probabilities of radiativeless transitions were evaluated from this comparison.  相似文献   

9.
The influence of polymer modifier chain length on the thermal conductivity of polyamide 6/graphene (GA) nanocomposites, including through-plane (λz) and in-plane (λx) directions were investigated. Here, three chain lengths of double amino-terminated polyethylene glycol (NH2–PEG–NH2) were used to covalently functionalize graphene with graphene content of 5.0 wt%. Results showed that λz was enhanced with the chain length of NH2–PEG–NH2 increased, but λx reached a maximum value at a certain chain length of NH2–PEG–NH2. The maximum λz and λx of GA are 0.406 W m−1 K−1 and 9.710 W m−1 K−1, respectively. This study serves as a foundation for further research on the thermal conductive property of graphene nanocomposites using different chain lengths of polymer modifier to improve the λz and λx of the thermal conductive materials.  相似文献   

10.
Ternary zinc–cobalt–copper alloys of wide range composition were deposited on to steel substrates from dilute metal sulphate bath. The bath consisted of 1–20 g dm−3 CuSO4·5H2O, 1–30 g dm−3 CoSO4·7H2O, 1–50 g dm−3 ZnSO4·7H2O, 20 g dm−3 Na2SO4 and 150–200 g dm−3 NH2CH2COOH. The effect of bath composition, current density and temperature on the cathodic potential, cathodic current efficiency and composition of the deposits were investigated. The codeposition of ZnCoCu alloys from these solutions can be classified as regular. Increasing current density enhances the rate of Zn deposition but suppresses that of Cu deposition. However, increasing the bath temperature favours Cu deposition. Co content in the deposits is hardly affected by changing these variables. Increasing Cu content in the bath or increasing the applied current density greatly improves the cathodic efficiency for the alloy deposition. X-ray diffraction studies showed that the deposits obtained at high current density (Zn-rich alloy) consisted of a cubic CuZn2 phase, while that obtained at high temperature (Cu-rich alloy) consisted of a face, centred cubic CuCo phase. The structure and morphology of the deposited alloys were characterised by anodic stripping and SEM.  相似文献   

11.
《Materials Letters》2007,61(11-12):2170-2172
Compression behaviour and micro-structure evaluation of Zr57Nb5Cu15.4Ni12.6Al10 bulk metallic glass is investigated at room temperature up to 32.8 GPa using in-situ high pressure energy dispersive X-ray diffraction with a synchrotron radiation source. The equation of state of the bulk metallic glass is − ΔV / V = 0.012P  2.49 × 10 4P2  9.5 × 10 7P3 + 5.02 × 10 8P4. The result shows that the nearest atom pair of the as-quenched bulk metallic glass corresponds to Zr–Zr correlations. And with pressure increasing, the nearest atom pair changes to a new one at 32.8 GPa.  相似文献   

12.
Control of chemical reactions is the essence of chemistry, producing designed outcomes while suppressing unwanted side products. Laser-assisted molecular vibrational control has been demonstrated to be a potential approach to influencing the outcome of a chemical reaction. In this article, we reviewed recent progress in the laser control of diamond synthesis through vibrational excitation of precursor molecules in a laser-assisted combustion chemical vapor deposition process. Significantly promoted diamond deposition rate (139 μm/h) and crystalline quality were achieved by resonantly exciting the Q-branch (ΔJ = 0) of the CH2-wagging mode (v7 mode 949.3 cm−1) of C2H4 molecules. Resonant excitation of the fundamental vibrational modes is more effective in promoting diamond growth than random vibrational excitation. Control of diamond crystallographic orientation was also realized by resonantly exciting the R branch (ΔJ = 1) of the CH2-wagging mode of C2H4 molecules and resulted in the preferential growth of {1 0 0}-oriented diamond crystals. Nitrogen-doped diamond films with a nitrogen concentration of 1.5 × 1020 atoms/cm3 were synthesized by resonantly exciting the rotational–vibrational transition (J = 5  J = 6, K = 0) of the N–H wagging mode (v2 mode) in ammonia molecules. The findings demonstrate the feasibility of laser-assisted vibrational control in steering chemical reactions and controlling reaction outcomes.  相似文献   

13.
《Thin solid films》2006,515(2):509-512
Silicon nitride (Si3N4) is an important insulator, frequently used in VLSI technology and for encapsulation. Conventionally it is prepared by low pressure and plasma-enhanced chemical vapour deposition, but may also be successfully deposited by RF sputtering. In the present work the sputtering process was characterised, together with some measurements on the high-field DC electrical properties in sandwich samples with Au electrodes. Films were Ar-sputtered using a Si3N4 sputtering target at gas pressures up to 2.12 Pa and RF discharge powers of 60–200 W. The deposition rate R was in the range 0.03–0.19 nm s 1 and was directly proportional to the discharge power and varied linearly with the pressure. Au electrodes formed sandwich structures with thicknesses of 50 nm–1 μm. Conductivity was essentially ohmic below 300 nm, while for the thicker films space-charge limited conductivity, dominated by an exponential distribution of traps, was observed. A mobility value of μ = 2.89 × 10 6 m2 V 1 s 1 was derived from temperature measurements, and further analysis of the JV data indicated a thermally generated electron concentration of 3.23 × 1019 m 3 and a trap concentration of 1.57 × 1024 m 3. It was concluded that this method is suitable for the deposition of thin films, which have similar electrical properties to those prepared by chemical vapour deposition methods.  相似文献   

14.
《Materials Letters》2005,59(19-20):2408-2411
The A-site deficient perovskite Nd2/3TiO3  δ was synthesized under an H2–CO2 gas mixture. The sample was found to have slight oxygen deficiency of δ∼0.012. The crystal structure was assigned to a double perovskite structure with orthorhombic space group Pmmm, as in the case of La2/3TiO3  δ. Electrical conductivity measurement has also been performed. The temperature dependence of conductivity shows that electronic transport in Nd2/3TiO2.988 is well described by Emin–Holstein adiabatic small polaron model. The polaron density extracted from the conductivity measurement is ∼1.96 × 1020 cm 3. This result agrees well with nominal polaron density for Nd2/3TiO2.988, ∼2.1 × 1020cm 3. We have also derived important quantities for transport in Nd2/3TiO2.988.  相似文献   

15.
《工程(英文)》2017,3(5):753-759
Although the effect of animal and diet factors on enteric methane (CH4) emissions from confined cattle has been extensively examined, less data is available regarding CH4 emissions from grazing young cattle. A study was undertaken to evaluate the effect of the physiological state of Holstein-Friesian heifers on their enteric CH4 emissions while grazing a perennial ryegrass sward. Two experiments were conducted: Experiment 1 ran from May 2011 for 11 weeks and Experiment 2 ran from August 2011 for 10 weeks. In each experiment, Holstein-Friesian heifers were divided into three treatment groups (12 animals/group) consisting of calves, yearling heifers, and in-calf heifers (average ages: 8.5, 14.5, and 20.5 months, respectively). Methane emissions were estimated for each animal in the final week of each experiment using the sulfur hexafluoride tracer technique. Dry matter (DM) intake was estimated using the calculated metabolizable energy (ME) requirement divided by the ME concentration in the grazed grass. As expected, live weight increased with increasing animal age (P < 0.001); however, there was no difference in live weight gain among the three groups in Experiment 1, although in Experiment 2, this variable decreased with increasing animal age (P < 0.001). In Experiment 1, yearling heifers had the highest CH4 emissions (g·d−1) and in-calf heifers produced more than calves (P < 0.001). When expressed as CH4 emissions per unit of live weight, DM intake, and gross energy (GE) intake, yearling heifers had higher emission rates than calves and in-calf heifers (P < 0.001). However, the effects on CH4 emissions were different in Experiment 2, in which CH4 emissions (g·d−1) increased linearly with increasing animal age (P < 0.001), although the difference between yearling and in-calf heifers was not significant. The CH4/live weight ratio was lower in in-calf heifers than in the other two groups (P < 0.001), while CH4 energy output as a proportion of GE intake was lower in calves than in yearling and in-calf heifers (P < 0.05). All data were then pooled and used to develop prediction equations for CH4 emissions. All relationships are significant (P < 0.001), with R2 values ranging from 0.630 to 0.682. These models indicate that CH4 emissions could be increased by 0.252 g·d−1 with an increase of 1 kg live weight or by 14.9 g·d−1 with an increase of 1 kg·d−1 of DM intake; or, the CH4 energy output could be increased by 0.046 MJ·d−1 with an increase of 1 MJ·d−1 of GE intake. These results provide an alternative approach for estimating CH4 emissions from grazing dairy heifers when actual CH4 emission data are not available.  相似文献   

16.
The paper describes the development and testing of an Inconel600 (2 mm diameter×21 cm long) self-powered neutron detector for in-core neutron monitoring. The detector has 3.5 mm overall diameter and 22 cm length and is integrally coupled to a 12 m long mineral insulated cable. The performance of the detector was compared with cobalt and platinum detectors of similar dimensions. Gamma sensitivity measurements performed at the 60Co irradiation facility in 14 MR/h gamma field showed values of −4.4×10−18 A/R/h/cm (−9.3×10−24 A/γ/cm2-s/cm), −5.2×10−18 A/R/h/cm (−1.133×10−23 A/γ/cm2-s/cm) and 34×10−18 A/R/h/cm (7.14×10−23 A/γ/cm2-s/cm) for the Inconel, Co and Pt detectors, respectively. The detectors together with a miniature gamma ion chamber and fission chamber were tested in the in-core Apsara Swimming Pool type reactor. The ion chambers were used to estimate the neutron and gamma fields. With an effective neutron cross-section of 4b, the Inconel detector has a total sensitivity of 6×10−23 A/nv/cm while the corresponding sensitivities for the platinum and cobalt detectors were 1.69×10−22 and 2.64×10−22 A/nv/cm. The linearity of the detector responses at power levels ranging from 100 to 200 kW was within ±5%. The response of the detectors to reactor scram showed that the prompt response of the Inconel detector was 0.95 while it was 0.7 and 0.95 for the platinum and cobalt self-powered detectors, respectively. The detector was also installed in the horizontal flux unit of 540 MW Pressurised Heavy Water Reactor (PHWR). The neutron flux at the detector location was calculated by Triveni code. The detector response was measured from 0.02% to 0.07% of full power and showed good correlation between power level and detector signals. Long-term tests and the dynamic response of the detector to shut down in PHWR are in progress.  相似文献   

17.
A novel low-temperature (600–850 °C), chemical vapor deposition method, involving a simple reaction between disiloxane (H3Si–O–SiH3) and ammonia (NH3), is described to deposit stoichiometric, Si2N2O, and non-stoichiometric, SiOxNy, silicon oxynitride films (5–500 nm) on Si substrates. Note, the gaseous reactants are free from carbon and other undesirable contaminants. The deposition of Si2N2O on Si (with (1 0 0) orientation and a native oxide layer of 1 nm) was conducted at a pressure of 2 Torr and at extremely high rates of 20–30 nm min−1 with complete hydrogen elimination. The deposition rate of SiOxNy on highly-doped Si (with (1 1 1) orientation but without native oxide) at 10−6 Torr was ∼1.5 nm min−1, and achieved via the reaction of disiloxane with N atoms, generated by an RF source in an MBE chamber. The phase, composition and structure of the oxynitride films were characterized by a variety of analytical techniques. The hardness of Si2N2O, and the capacitance–voltage (CV) as a function of frequency and leakage current density–voltage (JLV) characteristics were determined on MOS (Al/Si2N2O/SiO/p-Si) structures. The hardness, frequency-dispersionless dielectric permittivity (K), and JL at 6 V for a 20 nm Si2N2O film were determined to be 18 GPa, 6 and 0.05–0.1 nA cm−2, respectively.  相似文献   

18.
《Materials Research Bulletin》2006,41(7):1378-1384
The exploration of the Li–Ti–Mg–O system, using both sol–gel technique and solid state reaction method, allowed a new phase, Li2MgTiO4, with disordered rock salt structure (a = 4.159 Å) to be synthesized. The latter is shown to be a good type I dielectric material, with a relative constant of 15 at high frequency and low dielectric loss (tanδ < 10−3) over the temperature range −60 to 160 °C. It is also observed that the sintering temperature of this phase is strongly lowered by adopting the sol–gel technique compared to solid state reaction (1150 °C instead of 1300 °C). Finally we show that this phase exhibits cationic conductivity above 400 °C (σ600 °C = 9 × 10−5 S cm−1).  相似文献   

19.
There have been studied single crystals of undoped and doped Bi12TiO20 with two concentrations of W5+ (2.62 × 1017 cm−3 and 2.62 × 1018 cm−3). There have been obtained absorption spectra in the energy range of 10,482–15,408 cm−1 by classical measurements. There have been determined the cross-section (σa) of the impurity absorption and the oscillator strength of dd transitions. There have been calculated the refractive index of doped crystals and the concentration of Ti3+ ions in an undoped sample through an experiment.  相似文献   

20.
《Composites Part B》2013,45(1):686-691
New TiO2-based organic–inorganic porous hybrid materials were developed for color degradation and tested in azo-compounds aqueous solution. Porous composite materials, with pore size between 100 and 200 μm and pore volume fraction between 62% and 76%, were synthesized using micro-particles of TiO2 in anatase phase agglutinated with solvent-free, mono-component polyurethane; the pores were generated by the CO2 produced during the chemical reaction. The high porosity of the samples improves the contact with the colored solution increasing the photocatalytic effect. The degradation process was well fitted using a first order chemical reaction and the constant rate k determined. The best samples showed k values of 0.091 h−1 and 0.076 h−1 using visible light with a power of 100 mW/cm2 and k values of 1.465 h−1 and 1.652 h−1 using UV light with a power of 80 mW/cm2; these values are comparable or better to other reported in literature obtained under similar conditions. Additionally, the use of polyurethane increases the abrasion resistance improving the lifetime of the photocatalytic material. The materials were characterized using X-rays diffraction, SEM and UV–Vis spectroscopy.  相似文献   

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