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1.
A novel chemical method for the preparation of nanocrystalline MgAl2O4 spinel powders has been developed in this paper. The mixed magnesium-aluminum hydroxide precipitates were initially formed in a three-dimensional space network microarea. After being calcined at above 700 °C, the nanocrystalline MgAl2O4 spinel powders were obtained. The precursor and as-calcined powders were characterized using TGA-DTA, XRD and TEM. The MgAl2O4 spinel powders calcined at 850 °C for 2 h are of narrow distribution, little agglomeration and small particle size of ∼ 24 nm. The reason for the synthesis of high-quality powders was explained.  相似文献   

2.
The novel nano-ultrafine powders for the preparation of CaCu3Ti4O12 ceramic were prepared by the sol-gel method and citrate auto-ignition method. The obtained precursor powders were pressed, sintered at 1000 °C to fabricate microcrystal CaCu3Ti4O12 ceramic. The microcrystalline phase of CaCu3Ti4O12 was confirmed by X-ray powder diffraction (XRD). The morphology and size of the grains of the powders and ceramics under different heat treatments were observed using scanning electron microscopy (SEM). The relative dielectric constant of the ceramic sintered at 1000 °C was measured with a magnitude of more than 104 at room temperature, which was approaching to those of Pb-containing complex perovskite ceramics, and the loss tangent was less than 0.20 in a broad frequency region. The relative dielectric constant and loss tangent were also compared with that of CaCu3Ti4O12 ceramic prepared by other reported methods.  相似文献   

3.
L.H. Jiang  C.Y. Li  J.Q. Hao 《Materials Letters》2007,61(29):5107-5109
Borates LiSr4(BO3)3 were synthesized by high-temperature solid-state reaction. The thermoluminescence (TL) and some of the dosimetric characteristics of Ce3+-activated LiSr4(BO3)3 were reported. The TL glow curve is composed of only one peak located at about 209 °C between room temperature and 500 °C. The optimum Ce3+ concentration is 1 mol% to obtain the highest TL intensity. The TL kinetic parameters of LiSr4(BO3)3:0.01Ce3+ were studied by the peak shape method. The TL dose response is linear in the protection dose ranging from 1 mGy to 1 Gy. The three-dimensional thermoluminescence emission spectra were also studied, peaking at 441 and 474 nm due to the characteristic transition of Ce3+.  相似文献   

4.
The Fe3Si(24 nm)/CaF2(2 nm)/Fe3Si(12 nm) magnetic tunnel junction (MTJ) structures were grown epitaxially on CaF2/Si(111) by molecular beam epitaxy (MBE). The 12-nm-thick Fe3Si underlayer was grown epitaxially on CaF2/Si(111) at approximately 400 °C; however, the surface of the Fe3Si film was very rough, and thus a lot of pinholes are considered to exist in the 2-nm-thick CaF2 barrier layer. The average roughness (Ra) of the CaF2 barrier layer was 7.8 nm. This problem was overcome by low-temperature deposition of Fe and Si at 80 °C on CaF2/Si(111), followed by annealing at 250 °C for 30 min to form the Fe3Si layer. The Ra roughness was significantly reduced down to approximately 0.26 nm. A hysteresis loop with coercive field Hc of approximately 25 Oe was obtained in the magnetic field dependence of Kerr rotation at room temperature (RT).  相似文献   

5.
Nanoparticles of CdCO3 were synthesized by the reaction of Cd(CH3COO)2 and tetramethylammonium hydroxide (TMAH) by a sonochemical method. The CdO nanoparticles were obtained by heating of CdCO3 nanoparticles at 400 °C. The CdCO3 and CdO nanoparticles were characterized by scanning electron microscopy, X-ray powder diffraction (XRD), TGA, DTA and FT-IR spectroscopy.  相似文献   

6.
A simple co-precipitation technique has been successfully used for the preparation of pure ultrafine single phase BiTaO4. A standard ammonium hydroxide solution was used to precipitate Bi3+ and Ta5+ cations as hydroxides simultaneously under basic conditions. This precursor, on heating at 600 °C, produced product phase. This is the lowest temperature for the formation of BiTaO4 phase so far reported in the literature. For comparison BiTaO4 powders were also prepared by the traditional solid state method. The phase contents and lattice parameters were studied by the powder X-ray diffraction (XRD).  相似文献   

7.
Fresh niobium hydroxide was first precipitated from NbF5 solution using an aqueous ammonium hydroxide under basic conditions. Then a simple procedure of mixing lithium and niobium hydroxides together and heating at a low temperature (400 °C) produced pure ultrafine single phase LiNbO3 (LN). In the literature, this is the lowest temperature so far reported on the formation of LN. The phase content and lattice parameters are determined by X-ray diffraction (XRD). The average particle size and morphology were studied by transmission electron microscopy (TEM).  相似文献   

8.
Nanosized 0.6Li2MnO3·0.4LiCoO2 composite cathode powders are prepared by spray pyrolysis. The micron-sized composite powders are converted into nanosized powders by a simple milling process. The mean sizes of the composite powders measured from the TEM images increase from 20 to 170 nm when the post-treatment temperatures increase from 650 to 900 °C. The Brunauer–Emmett–Teller surface areas of the composite powders post-treated at 650 and 900 °C are 24 and 3 m2 g−1, respectively. The XRD patterns indicate that the layered composite powders post-treated at 800 and 900 °C have high crystallinity and low cation mixing. The mean crystallite sizes of the powders, measured from the (003) peak widths of the XRD patterns using Scherrer's equation, are 35 and 56 nm at post-treatment temperatures of 800 and 900 °C, respectively. The initial discharge capacities of the 0.6Li2MnO3·0.4LiCoO2 composite are 262, 267, 264, and 263 mAh g−1 when the post-treat temperatures of the powders are 650, 700, 800, and 900 °C, respectively. The discharge capacity of the composite powders post-treated at 900 °C abruptly decreases from 263 to 214 mAh g−1 by the seventh cycle and then slowly decreases to 198 mAh g−1 with increasing cycle number, up to 30.  相似文献   

9.
A new type of visible-light-driven photocatalyst BaCo0.5Nb0.5O3 was successfully synthesized via a sol-gel process in this study. After heating the precursors at 1000 °C, a pure perovskite phase was obtained. The particle size and crystallinity of BaCo0.5Nb0.5O3 powders markedly increased with a rise in the calcination temperature. The band gap of BaCo0.5Nb0.5O3 calculated from the UV-visible spectra was found to be less than that of titania. BaCo0.5Nb0.5O3 was demonstrated to have photocatalytic activity under visible light irradiation and this activity significantly depended on the synthesis temperature. The sol-gel derived powders were found to have better photocatalytic activity than the solid-state derived powders because of the reduced particle size and increased surface area.  相似文献   

10.
Cr1.8Ti0.2O3−δ (CTO) powders were prepared by citrate, sol-gel and solid-state routes, respectively. The effect of preparation methods on the morphology of sputtered thin films was further investigated. X-ray diffraction patterns of the powders and films confirmed a single phase CTO. No impurity was observed even after sintering the powders at 1000 °C for 24 h. X-ray photoelectron spectroscopy analysis showed that Cr 2p (577.8 eV), and O 1 s (531.5 eV) core levels of the sputtered films have ∼1 eV variation in their binding energy positions compared to those of CTO powders. The atomic force microscopy analysis showed the grains of the films obtained by sputtering sol-gel powders had the smallest size in the range of 7-58 nm. The surface roughness of the thin films had the lowest value at 0.70 nm, whereas those obtained from solid state solution had the maximum value of 2.51 nm.  相似文献   

11.
In this investigation, Fe3Mo3C ternary carbide was synthesized from the elemental powders of 3Mo/3Fe/C by mechanical milling and subsequent heat treatment. Structural and morphological evolutions of powders were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). Results showed that no phase transformation occurs during milling. A nanostructure Mo (Fe) solid solution obtained after 30 h of milling. With increasing milling time to 70 h no change takes place except grain size reduction to 9 nm and strain enhancement to 0.86%. Milled powders have spheroid shape and very narrow size distribution about 2 μm at the end of milling. Fe3Mo3C was synthesized during annealing of 70 h milled sample at 700 °C. Undesired phases of MoOC and Fe2C form at 1100 °C. No transformation takes place during annealing of 10 h milled sample at 700 °C. Mean grain size and strain get to 69 nm and 0.23% respectively with annealing of 70 h milled sample at 1100 °C.  相似文献   

12.
The fine powders of Bi3.25La0.75Ti3O12 (BLT) were prepared by coprecipitaton method in aqueous medium at low temperature. The differential thermal analysis (DTA), thermo-gravimetric analysis (TG) and X-ray diffraction (XRD) were employed to evaluate the phase formation of BLT and TEM was used to characterize and observe the particle size and morphology of BLT powder obtained. The results show that the bismuth layer perovskite phase of BLT can begin to form at as low as 500 °C by the coprecipitation method. When the precipitates obtained were calcined at 600 °C for 2 h, the mono-phase and perfect BLT powder was synthesized. The BLT powder obtained consists of irregular or plate-like particles which are less than about 100 nm and is nearly aggregate free.  相似文献   

13.
Eu3+ (2.5 at.%) and Tb3+ (0.005-0.01 at.%) co-doped gadolinium and yttrium oxide (Gd2O3 and Y2O3) powders and films have been prepared using the sol-gel process. High density and optical quality thin films were prepared with the dip-coating technique. Gadolinium (III) 2,4-pentadionate and yttrium (III) 2,4-pentadionate were used as precursors, and europium and terbium in their nitrate forms were used as doping agents. Chemical and structural analyses (infrared spectroscopy, X-ray diffraction and high-resolution transmission electron microscopy) were conducted on both sol-gel precursor powders and dip-coated films. The morphology of thin films heat-treated at 700 °C was studied by means of atomic force microscopy. It was shown that the highly dense and very smooth films had a root mean roughness (RMS) of 2 nm ± 0.2 (A = 0.0075 Tb3+) and 24 nm ± 3.0 (B = 0.01 Tb3+). After treatment at 700 °C, the crystallized films were in the cubic phase and presented a polycrystalline structure made up of randomly oriented crystallites with grain sizes varying from 20 to 60 nm. The X-ray induced emission spectra of Eu3+- and Tb3+-doped Gd2O3 and Y2O3 powders showed that Tb3+ contents of 0.005, 0.0075 and 0.01 at.% affected their optical properties. Lower Tb3+ concentrations (down to 0.005 at.%) in both systems enhanced the light yield.  相似文献   

14.
Gd2O3-WO3 complex ceramics are fabricated by the conventional solid-state reaction process. The electrical characteristics and dielectric properties of the samples were measured at various ambient temperatures in a low electric field (E < 150 V/mm). As the temperature increases, the dielectric constant and the loss tangent show an obvious change at about 50 °C and 330 °C. When the temperature is above 200 °C, the samples display stable nonlinear electrical properties characterized by semiconductivity, and the nonlinearity increases along with increasing temperature. XRD analysis reveals that Gd2W2O9 is the main phase and Gd2O3 is the secondary phase. Based on the phase transition of tungsten trioxide, these electrical properties of Gd2O3-WO3 complex ceramics can be simply explained.  相似文献   

15.
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   

16.
Eu3+ doped (Gd,Lu)2O3 nanopowders with particle sizes ranging from 20 to 70 nm were synthesized by the co-precipitant method using mixed precipitants, namely the mixture of ammonium hydroxide (NH3⋅H2O) and ammonium hydrogen carbonate (NH4HCO3). The precipitate precursor prepared by this method was believed to possess a basic carbonate composition and its thermal decomposition of the (Gd,Lu)2O3:Eu3+ powders were investigated by Thermogravimetric analysis and differential thermal analysis (TG-DTA). This preparation was followed by a calcination process at 800-1100 °C and corresponding phosphor structure were examined by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Photoluminescence measurement of the (Gd,Lu)2O3:Eu3+ particles show typical red emission at the 612 nm corresponding to the 5D0 → 7F2 transition. We found that the optimal Eu3+ molar doping concentration, calcined temperature and reaction time were 7 mol%, 1000 °C, and 2 h, respectively, which is helpful to obtain the final transparent ceramics with excellent properties.  相似文献   

17.
Hongxiao Yang 《Materials Letters》2010,64(13):1418-1420
In this work, we demonstrate that monodisperse indium hydroxide (In(OH)3) nanorods constructed with parallel wire-like subunits have been fabricated via a acrylamide-assisted synthesis route without any template. NH3 from the hydrolysis of acrylamide acts as the OH provider. The structure and morphology of as-prepared products have been characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HRTEM) and thermogravimetric analysis (TG). A detailed mechanism has been proposed on the basis of time-dependent experimental results. Furthermore, by annealing In(OH)3 precursors at 500 °C for 3 h in air, In2O3 samples were obtained with the designed morphology.  相似文献   

18.
The kinetic properties of monoclinic lithium vanadium phosphate were investigated by potential step chronoamperometry (PSCA) and electrochemical impedance spectroscopy (EIS) method. The PSCA results show that there exists a linear relationship between the current and the square root of the time. The D?Li values of lithium ion in Li3-xV2(PO4)3 under various initial potentials of 3.41, 3.67, 3.91 and 4.07 V (vs Li/Li+) obtained from PSCA are 1.26 × 10− 9, 2.38 × 10− 9, 2.27 × 10− 9 and 2.22 × 10− 9 cm2·s− 1, respectively. Over the measuring temperature range 15-65 °C, the diffusion coefficient increased from 2.67 × 10− 8 cm2·s− 1 (at 15 °C) to 1.80 × 10− 7 cm2·s− 1 (at 65 °C) as the measuring temperature increased.  相似文献   

19.
The nanocrystalline powders of pure and La3+-doped In2O3 with cubic structure were prepared by a simple hydrothermal decomposition route. The structure and crystal phase of the powders were characterized by X-ray diffraction (XRD) and microstructure by transmission electron microscopy (TEM). All the compositions exhibited a single phase, suggesting a formation of solid solution in the concentration of doping investigated. Gas-sensing properties of the sensor elements were tested by mixing a gas in air at static state, as a function of concentration of dopant, operating temperature and concentrations of the test gases. The pure In2O3 exhibited high response towards H2S gas at an operating temperature 150 °C. Doping of In2O3 with La3+ increases its response towards H2S and La3+ (5.0 wt.% La2O3)-doped In2O3 showed the maximum response at 125 °C. The selectivity of the sensor elements for H2S against different reducing gases was studied. The results on response and recovery time were also discussed.  相似文献   

20.
Preparation of BaTiO3 nanopowders (37-42 nm) is carried out by a controlled reconstructive thermal decomposition and crystallization from an amorphous polymeric precursor with polyvinyl alcohol (PVA) and sucrose at 400-600 °C in air. The Rietveld refinement of the XRD profile, processed at 600 °C in 2 h, infers the P4mm tetragonal crystal structure (95% of tetragonality) of the as prepared BaTiO3 nanopowders, with a = 0.3994 nm and c = 0.4024 nm. A cubic symmetry (Pm3m) of 5% in amount with a = 4.0057 is also detected in addition with tetragonal symmetry. The characteristic tetragonal splitting of 002/200 XRD peaks also supports the tetragonal symmetry (c / a = 1.0075) of the as prepared BaTiO3 nanopowders. The average particle size (D) of the BaTiO3 powders, estimated with the help of the specific surface area, measured by BET method, is 39.91 nm. Average D value, calculated by Δ2θ1 / 2 in the XRD peaks with the Debye Scherrer relation is ∼ 40 nm. TEM study measures the particle size of the BaTiO3 powders with an average diameter of 37 to 42 nm.  相似文献   

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