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1.
Four methods including hydrothermal method, glycol‐hydrothermal method, microwave‐hydrothermal method and glycol‐microwave‐hydrothermal method were used to prepare magnesium oxide precursor by the reaction of MgSO 4·7H 2O with (NH 4) 2CO 3. The composition, crystallinity, morphology, aspect ratio, yield, functional groups, atom distribution, and interplanar spacing of the sample were investigated by X‐ray diffraction (XRD), Scan Electron Microscope (SEM), Fourier Transform Infrared Spectroscopy (FT‐IR), and High Resolution Transmission Electron Microscope (HRTEM). The properties of Magnesium Oxide precursor were compared with each other. The results of FT‐IR and XRD showed that the crystals were all nesquehonite. However, it was shown by FT‐IR results that the crystals prepared by glycol‐microwave‐hydrothermal method contained OH − and HCO 3− groups, which indicated that the Mg(OH)(HCO 3)·2H 2O type crystals would be facilitated by this method. The glycol‐hydrothermal method can create high quality Magnesium Oxide precursor with a high degree of crystallinity, high purity, high aspect ratio, smooth surface, and good dispersibility. 相似文献
2.
D‐optimal experimental design with three levels of SiO 2/Al 2O 3, template/SiO 2, H 2O/SiO 2, SiO 2/Na 2O and TPABr/TPAOH ratio parameters was used to optimize the experimental parameters by the analysis of variance (ANOVA). The effects of above mentioned ratios in the initial synthetic mixture on the crystallinity of the ZSM‐5 zeolite were studied. The synthesized samples were characterized by XRD, FE‐SEM, and TEM analysis. Fischer test results showed that SiO 2/Al 2O 3 and H 2O/SiO 2 molar ratios are the most and least effective parameters, respectively, in the range studied. The most important two‐way interaction variable was that of template/SiO 2 and Na 2O/SiO 2 molar ratios. The optimum composition of the gel compound to achieve relative maximum crystallinity is SiO 2/Al 2O 3 = 99.96, template/SiO 2 = 0.16, H 2O/SiO 2 = 34.68, Na 2O/SiO 2 = 0.02 and TPABr/TPAOH = 1.44. 相似文献
3.
(1 − x)Li 2O– xNa 2O–Al 2O 3–4SiO 2 glasses were studied for the progressive percentage substitution of Na 2O for Li 2O at the constant mole of Al 2O 3 and SiO 2. The crystallization temperature at the exothermic peak increased from 898 to 939 °C when the Na 2O content increases from 0 to 0.6 mol. The coefficient of thermal expansion and density of these as-quenched glasses increase from 6.54 × 10 −6 °C −1 to 10.1 × 10 −6 °C −1 and 2.378 g cm −3 to 2.533 g cm −3 when the Na 2O content increases from 0 to 0.4 mol, respectively. The electrical resistivity has a maximum value at Na 2O · (Li 2O + Na 2O) −1 = 0.4. The activation energy of crystallization decreases from 444 to 284 kJ mol −1 when the Na 2O content increased from 0 to 0.4 mol. Moreover, the activation energy increases from 284 kJ mol −1 to 446 kJ mol −1 when the Na 2O content increased from 0.4 to 0.6 mol. The FT-IR spectra show that the symmetric stretching mode of the SiO 4 tetrahedra (1035–1054 cm −1) and AlO 4 octahedra (713–763 cm −1) exhibiting that the network structure is built by SiO 4 tetrahedra and AlO 4. 相似文献
4.
The Li 2Al 2Si 3O 10 glass-ceramics well crystallized and with a regular morphology was produced starting from a mixture of Li 2CO 3, TiO 2, Al 2O 3 and coal bottom ash, after reducing the magnetite phase content. Its measured thermal expansion coefficient in the temperatures range from 25 °C to 300 °C is α(25–300) = −23.4 × 10 −7 °C −1. This value is ≈18% smaller than that for the commercial lithium glass-ceramics (−23.4 × 10 −7 °C −1 to 50 × 10 −7 °C −1). 相似文献
5.
A neodymium doped Ca 5(BO 3) 3F single crystal with size up to 51×48×8 mm 3 has been grown by the top seeded solution growth (TSSG) technique with a Li 2O‐B 2O 3‐LiF flux. The spectra of absorption and fluorescence were measured at room temperature. According to Judd‐Ofelt (J‐O) theory, the spectroscopic parameters were calculated and the J‐O parameters Ω 2, Ω 4, Ω 6 were obtained as follows: Ω 2 = 1.41×10 −20cm 2, Ω 4 = 3.18×10 −20cm 2, Ω 6 = 2.11×10 −20cm 2. The room temperature fluorescence lifetime of NCBF was measured to be 51.8 μs. According to the J‐O paramenters, the emission probabilities of transitions, branching ratios, the radiative lifetime and the quantum efficiency from the Nd 3+ 4F 3/2 metastable state to lower lying J manifolds were also obtained. In comparasion with other Nd‐doped borate crystals, the calculated and experimental parameters show that NCBF is a promising SFD crystal. 相似文献
6.
Praseodymium-doped GaAs and Al 0.3Ga 0.7As epilayers grown on Semi-Insulating (SI) GaAs substrates by Liquid Phase Epitaxy (LPE) were first studied in this present work. Measurement techniques, such as microscopic observation, X-ray diffraction, Secondary Ion Mass Spectroscopy (SIMS), and Hall measurement were employed. Layers doped with Pr resulted in a mirror-like surface, except several high Pr-doped layers having droplet surfaces. Hall measurements reveal that the grown layers contained p-type layers, carrier concentrations from 6.3 × 10 15 to 1.2 × 10 16 cm −3, and from 6.3 × 10 15 to 3.5 × 10 16 cm −3 for Pr-doped GaAs and Al 0.3Ga 0.7As epilayers, respectively. Although p-type conduction exists, in the light of electrical features, doping of Pr into the GaAs and Al 0.3Ga 0.7As growth melts, is still considered to exhibit gettering properties rather than to become a new acceptor itself. Additional photoluminescence examinations were taken. Their results also indicate that Pr-doped layers produce no new emission lines and support the electrical observations. 相似文献
7.
The growth of calcite crystals from an aqueous supersaturated solution of initial concentration 0.15 mol m −3 containing 10 mol m −3 of (NH 4) 2CO 3 has been studied at 298 K. The progress of growth has been followed through determining the composition of the solution by chemical analysis. The crystal growth is controlled by the surface reaction mechanism and satisfies a kinetic equation of the second order with the rate constant 3.7 × 10 −6 m 4 mol −1 s −1 that is independent on the surface area of the present solid. NH 4+ ions do not change the crystal growth mechanism but decrease the growth rate of calcite crystals. 相似文献
8.
Pure and indium doped antimony telluride (Sb 2Te 3) crystals find applications in high performance room temperature thermoelectric devices. Owing to the meagre physical properties exhibited on the cleavage faces of melt grown samples, an attempt was made to explore the thermoelectric parameters of p‐type crystals grown by the physical vapor deposition (PVD) method. The crystal structure of the grown platelets (9 mm× 8 mm× 2 mm) was identified as rhombohedral by x‐ray powder diffraction method. The energy dispersive analysis confirmed the elemental composition of the crystals. The electron microscopic and scanning probe image studies revealed that the crystals were grown by layer growth mechanism with low surface roughness. At room temperature (300 K), the values of Seebeck coefficient S (⊥ c) and power factor were observed to be higher for Sb 1.8In 0.2Te 3 crystals (155 μVK −1, 2.669 × 10 −3 W/mK 2) than those of pure ones. Upon doping, the thermal conductivity κ (⊥ c) was decreased by 37.14% and thus thermoelectric efficiency was improved. The increased figure of merit, Z = 1.23 × 10 −3 K −1 for vapour grown Sb 1.8In 0.2Te 3 platelets indicates that it could be used as a potential thermoelectric candidate. 相似文献
9.
Lead titanate thin films were prepared in-situ by RF magnetron sputtering method in the substrate temperature region of 550 °C ˜ 650 °C using Ti and Pb metal targets and oxygen gas. The films deposited at 650 °C for 60 min – when the applied power to the Ti and Pb target and deposition pressure were 200 W, 40 W, and 1.8 × 10 −2 Torr, respectively — had stoichiometric composition ratio and shown X-ray diffraction patterns of tetragonal structure like that of the powder. For the application to the piezoelectric field effect transistor (PI-FET), the substrate of SiO 2 (50 nm)/p-Si(100) was used. Leakage current density of the thin film was 7 × 10 −8 A/cm 2 at 100 kV/cm, dielectric breakdown voltage was 1.8 MV/cm, and so it showed high insulator characteristics. Capacitance-voltage curve was measured as a function of pressure. The variation width of the capacitance was 6.5 pF at bias voltage of –4 volts, and the value increased linearly according to the pressure up to about 6 kgf/cm 2, and was saturated at the pressure of 8 kgf/cm 2. 相似文献
10.
A new hydroxylammonium compound, [(NH 3OH) 2CuCl 4], was synthesized and its crystals were grown at room temperature by slow evaporation of aqueous solutions. The crystals were characterized through powder XRD, thermogravimetry (TG), differential thermal analysis (DTA), low temperature differential scanning calorimetric (DSC) and FTIR spectra. The X‐ray powder diffraction confirms the crystallinity of the compound. A fitting decomposition pattern of the compound was formulated based on the TG and thereby confirming the formation of the compound in the stoichiometric ratio. The thermal anomalies occurring in the low temperature DSC indicate successive phase transitions. The low temperature phase transitions are attributed to the ordering of [NH 3OH] + ions. While most of the phase transitions are of first order type, the one occurring at –126 °C is of second order. Two glass transitions occur when the compound was cooled between –157.9 and –136.9 °C. The characteristic vibration bands due to [NH 3OH] + and CuClequation/tex2gif-stack-1.gif ions are observed in the IR spectra. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
11.
The influence of the size of Y2O3 powder particles on the structure formation and densification of Nd3+:Y3Al5O12 laser ceramics has been studied. It is shown that the use of 50- and 100-nm yttrium oxide particles makes it possible to synthesize single-phase yttrium aluminum garnet at temperatures of 1200 and 1500°C, respectively, whereas in the case of 5000-nm yttrium oxide particles 2-h exposure at a temperature of 1500°C yields only 80 wt % of the Nd3+:Y3Al5O12 phase. Bulk swelling of pressed samples during sintering of 2.94Y2O3-0.06Nd2O3-5Al2O3 powders with the size ratio of the initial particles R(Al2O3/Y2O3) ~ 5 is observed. The application of different-sized powders (R ~ 2.5) provides quantitative ratios between phases in the 3Y2O3-5Al2O3 system at which shrinkage in a temperature range of 20–1500°C is dominant. Laser ceramics 0–2 at % Nd3+:Y3Al5O12 have been obtained by the solid-phase sintering of oxide powders (R ~ 2.5). The slope efficiency for 1 at % Nd3+:Y3Al5O12 laser ceramics is found to be 33%. 相似文献
12.
Mullite‐type Bi 2Ga 4O 9 single‐crystals were grown by the top‐seeded solution growth (TSSG) method and investigated by vibrational spectroscopy. Polarised IR specular reflectance and attenuated total reflectance (ATR) spectra, as well as polarised micro‐Raman spectra were acquired at room temperature. Powder IR spectra of sol‐gel‐derived samples were also recorded. Using model calculations and comparison to other mullite‐type compounds, bands at ∼ 850 – 400 cm ‐1 could be assigned to stretching and bending vibrations of the structural GaO 4 and GaO 6 units. Low‐energetic modes were attributed to motions involving Bi atoms. The IR spectra of Bi 2Ga 4O 9 display close similarities to those of the mullite‐type alkali gallates (9Ga 2O 3 · Rb 2O), while their differences to those of mullite sensu stricto (3Al 2O 3 · 2SiO 2 and 2Al 2O 3 · SiO 2, repectively) are assigned to Si‐O stretching vibrations of the corresponding tetrahedral units. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
13.
On the basis of the known data on the (NH 4)H 2PO 4-KCl-KNO 3-H 2O system, 65.0 × 9.0 × 8.0-mm 3-large crystals of the [K 0.75(NH 4) 0.25]H 2PO 4 solid solutions are grown on seed by the method of temperature decrease. It is shown that the 60.0 × 17.0 × 10.0 mm 3-large KH 2PO 4 crystals contain impurities: 6.0 × 10 −3 wt % Li and 0.1 wt % Na.
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Translated from Kristallografiya, Vol. 50, No. 4, 2005, pp. 761–764.
Original Russian Text Copyright ? 2005 by Soboleva. 相似文献
14.
The investigation covers a temperature range from 200 to 450 K. Thermoelectric power measurements of In 2S 3 crystals showed that all samples under investigation have a positive TEP in all temperature ranges, indicating n-type conductivity for In 2S 3 crystals. The ratio of the electron and hole mobilities is μ n/μ p = 4.71. The effective mass of electrons m is found to be 0.00008 × 10 −31 kg. The obtained effective masses of holes m = 1.893 × 10 −31 kg. The diffusion coefficient for both carriers (electrons and holes) is evaluated to be 84.71 cm 2/s and 17.985 cm 2/s respectively. The mean free time between collision is estimated to be τ n = 1.7 × 10 −20s, and τ p = 8.5 × 10 −17s. The estimated diffusion length for electrons is found to be Ln = 1.2 × 10 −9 cm and Lp = 3.9 × 10 −8 cm. 相似文献
15.
Ti–Al co-doped erbium tellurite glasses have been obtained by melting mixed Er 2O 3, TiO 2 and TeO 2 batches in Al 2O 3 crucibles. By crucible dissolution Al 2O 3 amounts from 11.5 to 18.6 mol% were introduced in the synthesized glasses. Differential thermal analysis of glasses points to a strong dependence of glass transition temperature Tg with the substitution extent of TeO 2 by the doping oxides. No crystallization features are observed up to 450 °C. The spectral features and decay kinetics of the infrared photoluminescence of erbium demonstrate the possibility to achieve more than 50% of quantum yield of light-emission at Er 3+ concentrations as large as 10 21 cm −3, with about 2 ms of lifetime, 8 × 10 −21 cm 2 of stimulated emission cross section, and no saturation at pump power densities higher than 10 kW cm −2. The study of the kinetics of Er–Er energy transfer suggests to ascribe these features to a particularly homogeneous dispersion of Er 3+ ions in the modified tellurite network. Raman scattering measurements of the spectral distribution of vibrational modes evidence that the introduction of doping oxides leads to an increase of structural disorder without crystallization effects. 相似文献
16.
The room temperature epitaxial growth of CeO 2 on lattice matched (001) LaAlO 3 substrates by using pulsed laser deposition (PLD) method under various oxygen partial pressure (Po 2) is demonstrated. X‐ray diffraction analysis with 2‐Theta/rocking curve/Phi‐scan, cross‐sectional transmission electron microscopy with selected‐area diffractions are used to characterize structural of grown films. The epitaxial (001) CeO 2 can be achieved at room temperature under Po 2 less than 2 × 10 −3 Torr. The best quality of grown film is obtained under Po 2 = 2 × 10 −5 Torr and degraded under Po 2 = 2 × 10 −6 Torr due to oxygen deficiency in structure. The epitaxial relationship between CeO 2 and LAO is confirmed to be (001)CeO 2 //(001)LAO, [100] CeO2//[110] LAO and [010] CeO2//[10] LAO. No obvious reduction reaction occurred, from Ce +4 turned into Ce +3 states, as reducing oxygen partial pressure during growth by PLD. 相似文献
17.
In this paper, [NaGd 1‐xNdx](MoO 4) 2 crystals with x = 0.005–0.05 were grown by Czochralski method at 950 ℃ for 10 hours and subsequently characterized by absorption spectroscopy and fluorescence spectroscopy. The intensity parameters of Nd 3+ were calculated by Judd‐Ofelt theory, and the relationship between the parameters and Nd 3+ concentration was analyzed. The results show that with the increasing Nd 3+ concentration, the oscillator strength, stimulated emission cross‐section, Ω t and spontaneous transition probability decrease slightly, while the fluorescence lifetime decreases significantly. However, the fluorescence branching ratio is almost unchanged with the increasing Nd 3+concentration. The [NaGd 1‐xNd x](MoO 4) 2 crystal with ( x = 0.01) possesses the highest quantum efficiency of 88.98%, a good fluorescence line‐width of 23 nm, a large value of σ em·τ f up to 0.55 × 10 −22 cm 2·s and a stimulated emission cross‐section up to 3.747 × 10 −19 cm 2 for the transition from 4F3/2 to 4I11/2 at 1064 nm. Test results indicate that [NaGd 1‐xNd x](MoO 4) 2 crystals are an excellent gain media for the solid state laser system. 相似文献
18.
Anomalous SiO 2 films have been prepared by sputtering Si in a mixture of Ar-10% O 2 at 77 K. The same sputtering conditions at room temperature yield normal SiO 2 which means that the anomaly is produced by the low temperature deposition. The anomaly reveals itself in several physical properties. The density of the anomalous SiO 2 is 1.72 as compared with 2.20 for bulk and the dielectric constant is about 50% larger than bulk and with a much stronger temperature dependence. The infrared (ir) spectrum of the anomalous SiO 2 is only slightly different from bulk SiO 2 but esr experiments reveal about 3 × 10 18 spins cm which do not exist in bulk SiO 2. These anomalous films are extremely stable: upon heating only a small amount of oxygen (1 part in 10 5) evolves at 440°C but the density and IR spectrum remain unchanged up to 1300°C. Annealing at 1500°C completely removes the ESR signal and returns the ir spectrum and the density to that of cristobalite. An electron diffraction and transmission electron microscopy study reveals that the anomalous SiO 2 films consist of essentially bulk like SiO 2 clusters about 250 Å in diameter separated by a low density network. The low density network undoubtedly contains unbound O atoms and the SiSi bonds which give rise to the esr signal. The structural model can account for all the anomalous properties. 相似文献
19.
Titanium dioxide films have been deposited using DC magnetron sputtering technique onto silicon substrates at an ambient temperature and at an oxygen partial pressure of 7 × 10 –5 mbar and sputtering pressure (Ar + O 2) of 1 × 10 –3 mbar. The deposited films were calcinated at 673 and 773 K. The composition of the films as analyzed using Auger Electron Spectroscopy (AES) revealed the stoichiometry with an O and Ti ratio of 2.08. The influence of post‐deposition calcination on the Raman scattering of the films was studied. The existence of Raman active modes A 1g, B 1g and E g corresponding to the Raman shifts are reported in this paper. The improvement of crystallinity of the TiO 2 films as shown by the Raman scattering studies has also been reported. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
20.
Low-frequency (<1000 cm −1) Raman scattering of lithium aluminosilicate (12Li 2O : 15Al 2O 3 : 73SiO 2 with 4 mol% TiO2) glasses with addition of titanium dioxide has been studied. With a heat treatment at temperatures 660°C, 700°C, 720°C and 820°C and for various times and sequences of temperature, our samples decompose into nanometer sized dispersed aluminotitanate particles. In Raman spectra of these glasses an evolution of a boson peak was observed. The width of the relatively broad boson band decreases as does the frequency of the band. From small-angle X-ray scattering data we conclude that the boson peak is connected with elastic vibrations of amorphous or crystalline regions of inhomogeneity with a dimension of ∼1.7 nm in initial glasses or larger depending on the heat treatment sequences. 相似文献
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