共查询到20条相似文献,搜索用时 250 毫秒
1.
Shiwen Shu Dabin YuYan Wang Feng WangZirong Wang Wu Zhong 《Journal of Crystal Growth》2010,312(21):3111-3116
This paper reports on the thermal-induced performance of hexagonal metastable In2O3 nanocrystals involving in phase transition and assembly, with particular emphasis on the assembly for the preparation of functional materials. For In2O3 nanocrystals, the metastable phase was found to be thermally unstable and transform to cubic phase when temperature was higher than 600 °C, accompanied by assembly as well as evolution of optical properties, but the two polymorphs coexisted at the temperature ranging from 600 to 900 °C, during which the content of product phase and crystal size gradually increased upon increasing temperature. The assembly of In2O3 nanocrystals can be developed to fabricate In2O3 functional materials, such as various ceramic materials, or even desired nano- or micro-structures, by using metastable In2O3 nanocrystals as precursors or building blocks. The electrical resistivity of In2O3 conductive film fabricated by a hot-pressing route was as low as 3.72×10−3 Ω cm, close to that of In2O3 single crystal, which is important for In2O3 that is always used as conductive materials. The findings should be of importance for both the wide applications of In2O3 in optical and electronic devices and theoretical investigations on crystal structures. 相似文献
2.
The effect of Y2O3 addition on the phase transition and growth of yttria-stabilized zirconia (YSZ) nanocrystallites prepared by a sol-gel process with various mixtures of ZrOCl2 · 8H2O and Y(NO3)3 · 6H2O ethanol-water solutions at low temperatures has been studied. DTA/TGA, XRD, SEM, TEM and ED have been utilized to characterize the YSZ nanocrystallites. The crystallization temperature of 3YSZ, in which Y2O3/(Y2O3 + ZrO2) = 0.03, gel powders estimated by DTA/TG is about 427 °C. When 3YSZ and 5YSZ gels are calcined at 500-700 °C, their crystal structures as composed of coexisting tetragonal and monoclinic ZrO2, and tetragonal phase decreases with calcination temperature increasing from 500 to 700 °C. Pure cubic ZrO2 is obtained when added Y2O3 is greater than 8 mol%. A nanocrystallite size distribution between 10 and 20 nm is obtained in TEM observations. 相似文献
3.
Co2+-doped MgAl2O4 nanocrystalline powders were prepared by co-precipitation method. The gels and/or calcined samples were characterized by means of thermogravimetry and differential scanning calorimetry (TG/DSC), X-ray diffraction (XRD), transmission electron microscope (TEM), Fourier transform infrared (FTIR) spectrum and near-infrared absorption spectrum. MgAl2O4 nanocrystals were produced by calcining the gel above 800 °C, with the crystallite size of 10-30 nm in the temperature range of 800-1100 °C. The influence of pH value of precipitant solution on the dispersing of powders was studied and the result showed that Co:MgAl2O4 nanocrystalline powders exhibited good dispersion when pH = 11. The absorption spectrum of Co2+-doped MgAl2O4 exhibited a broad absorption band in the wavelength range of 1200-1600 nm, which indicated that Co2+ ions substituted for the tetrahedrally coordinated Mg2+ ions in the MgAl2O4 lattice. 相似文献
4.
Xue-min Cui Le-ping Liu Guang-jian Zheng Rui-ping Wang Jian-ping Lu 《Journal of Non》2010,356(2):72-12
Pure chemosynthetic Al2O3-2SiO2 geoploymers displaying positive alkali-activated polymerization properties and high compressive strength at room temperature were effectively fabricated utilizing a sol-gel method. The molecular structure of the precursor powder and resulting geopolymers were investigated by X-ray diffraction (XRD) and nuclear magnetic resonance (NMR) analysis. In addition, the mechanical and alkali-activated polymerization properties of these materials were also studied. NMR data revealed that the chemosynthetic powders began to contain 5-coordinated Al atoms when the calcination temperatures exceeded 200 °C. These calcined powders were capable of reacting with sodium silicate solutions at calcination temperatures exceeding 300 °C, which is, however, much lower than the temperature required to convert kaolin to Metakaolin. 相似文献
5.
Gd2O3-doped CeO2 (Gd0.1Ce0.9O1.95, GDC) thin films were synthesized on (1 0 0) Si single crystal substrates by a reactive radio frequency magnetron sputtering technique. Structures and surface morphologies were characterized by X-ray diffraction (XRD), Atomic Force Microscopy (AFM) and one-dimensional power spectral density (1DPSD) analysis. The XRD patterns indicated that, in the temperature range of 200–700 °C, f.c.c. structured GDC thin films were formed with growth orientations varying with temperature—random growth at 200 °C, (2 2 0) textures at 300–600 °C and (1 1 1) texture at 700 °C. GDC film synthesized at 200 °C had the smoothest surface with roughness of Rrms=0.973 nm. Its 1DPSD plot was characterized with a constant part at the low frequencies and a part at the high frequencies that could be fitted by the f−2.4 power law decay. Such surface feature and scaling behavior were probably caused by the high deposition rate and random growth in the GDC film at this temperature. At higher temperatures (300–700 °C), however, an intermediate frequency slope (−γ2≈−2) appeared in the 1DPSD plots between the low frequency constant part and the high frequency part fitted by f−4 power law decay, which indicated a roughing mechanism dominated by crystallographic orientation growth that caused much rougher surfaces in GDC films (Rrms>4 nm). 相似文献
6.
(30 − x/2)Li2O·(70 − x/2)B2O3·xAl2O3(x = 0, 5 and 10) composite gels have been fabricated by the sol-gel method. LiOCH3, B(OC4H9)3, and Al(OC4H9)3 were used as precursor for Li2O, B2O3, and Al2O3, respectively. B(OC4H9)3 and Al(OC4H9)3 were hydrolyzed separately and then mixed. The crystallization behavior and structure of the gels upon thermal treatment temperatures between 150 and 550 °C are characterized on the basis of SEM, XRD and IR analyses. Xerogel with x = 0 exhibits non-crystal features, whereas crystalline phases are found in the xerogels with x = 5 and 10. The crystalline phases are not found with increasing heat treatment temperatures from 150 to 450 °C, but crystalline phases appear present at 550 °C. The xerogel with x = 0, subject to thermal treatment below 450 °C, is found to be still amorphous, and a 550 °C heat treatment leads its structure changing from glassy to crystalline. 相似文献
7.
Kazuhiro Akiyama Yasuhiro Ishii Hisashi Murakami Yoshinao Kumagai Akinori Koukitu 《Journal of Crystal Growth》2009,311(10):3110-3113
Surface reactions between a (0 0 0 1) C-plane sapphire and NH3, with He as an inert carrier gas, were investigated at high temperatures over 1200 °C using the in situ gravimetric monitoring method. Although the sapphire substrate was stable up to 1400 °C under a He atmosphere, decomposition started to occur at 1300 °C under a 0.1 atm NH3+He and the decomposition rates were found to be lower than those in 0.1 atm H2+He at each temperature. These results imply that sapphire can be decomposed by NH3 and/or hydrogen generated by the decomposition of NH3 over 1300 °C. The decomposition rate in NH3+He was decreased with increase in NH3 flow time, and the decomposition rate became constant after 60 min of NH3 flow. Moreover, the activation energy for sapphire decomposition before 60 min of NH3 flow was different from that after 60 min of NH3 flow time, which indicates that the surface reaction between sapphire and NH3 and/or hydrogen generated from NH3 changes depending on the time of NH3 flow. The dependence of the surface reactions and rate-limiting reactions between sapphire and NH3 on the time of NH3 flow is discussed. 相似文献
8.
Dan Seguin Madhana Sunder Lakshmi Krishna Alexander Tatarenko P.D. Moran 《Journal of Crystal Growth》2009,311(12):3235-3238
Fe0.8Ga0.2 films were deposited on bulk single-crystal (0 0 1) 0.69PMN-0.31PT substrates by DC magnetron sputtering to make magnetoelectric bilayer composites. Films deposited at temperatures below 600 °C were X-ray amorphous. Films deposited at temperatures of 600 °C and higher exhibited a single-crystal (0 0 1) disordered BCC structure. The crystalline FeGa films demonstrate a 45° twisted cube-on-cube epitaxial relationship with the PMN–PT substrates. Heterostructures with an X-ray amorphous FeGa film exhibited zero magnetoelectric response. Heterostructures with a 990 nm epitaxial FeGa film exhibited a large inverse magnetoelectric voltage coefficient of 13.4 (G cm)/V. 相似文献
9.
Saswati Ghosh 《Journal of Non》2008,354(34):4081-4088
Several compositions based on BaO-CaO-Al2O3-SiO2 (BCAS) glass system have been studied in this investigation to see their applicability as sealant for solid oxide fuel cell (SOFC). The glasses as well as the corresponding glass-ceramics have been systematically characterized by differential thermal analysis, dilatometry, X-ray diffractometry, electron microscopy and impedance analysis to examine their suitability as sealant. While the glass transition temperature (Tg) determined from DTA are within 600-665 °C, the coefficient of thermal expansion (CTE) can be tailored between 9.5 and 13.0 × 10−6 K−1. These glasses are found to be well adhered with metallic interconnects, such as commercial ferritic steel (Crofer22APU), at an optimum sealing temperature of 850 °C. The shrinkage behavior of the developed glasses in their pellet form has also been investigated. The resistivities of the glass-ceramics, as obtained from impedance analysis, are found to be within 104-106 Ω cm at 800 °C. Under sandwiched condition between two metals, some of the developed compositions are found to maintain this high resistivity even after 100 h of operation. One of the glass compositions has shown a low leak-rate of the order of ∼10−7 Pa m2 s−1. 相似文献
10.
M.C. Rao 《Journal of Crystal Growth》2010,312(19):2799-2803
Thin films of LiCoO2 were prepared by pulsed laser deposition technique and the properties were studied in relation to the deposition parameters. The films deposited from a sintered composite target (LiCoO2+Li2O) in an oxygen partial pressure of 100 mTorr and at a substrate temperature of 300 °C exhibited preferred c-axis (0 0 3) orientation perpendicular to the substrate surface. The AFM data demonstrated that the films are composed of uniform distribution of fine grains with an average grain size of 80 nm. The grain size increased with an increase in substrate temperature. The (0 0 3) orientation decreased with increase in (1 0 4) orientation for the films deposited at higher substrate temperatures (>500 °C) indicating that the films’ growth is parallel to the substrate surface. The composition of the experimental films was analyzed using X-ray photoelectron spectroscopy (XPS). The binding energy peaks of Co(2p3/2) and Co(2p1/2) are, respectively, observed at 779.3 and 794.4 eV, which can be attributed to the Co3+ bonding state of LiCoO2. The electrochemical measurements were carried out on Li//LiCoO2 cells with a lithium metal foil as anode and LiCoO2 film as cathode of 1.5 cm2 active area using a Teflon home-made cell hardware. The Li//LiCoO2 cells were tested in the potential range 2.6-4.2 V. Specific capacity as high as 205 mC/cm2 μm was measured for the film grown at 700 °C. The growth of LiCoO2 films were studied in relation to the deposition parameters for their effective utilization as cathode materials in solid-state microbattery application. 相似文献
11.
Hajime Kiyono Toshiki SakaiMari Takahashi Shiro Shimada 《Journal of Crystal Growth》2010,312(19):2823-2827
Thermogravimetric analysis (TGA) and microstructural observations were carried to investigate the nitridation mechanism of β-Ga2O3 powder to GaN under an NH3/Ar atmosphere. Non-isothermal TGA showed that nitridation of β-Ga2O3 starts at ∼650 °C, followed by decomposition of GaN at ∼1100 °C. Isothermal TGA showed that nitridation follows linear kinetics in the temperature range 800–1000 °C. At an early stage of nitridation, small GaN particles (∼5 nm) are deposited on the β-Ga2O3 crystal surface and they increase with time. We proposed a mechanism for the nitridation of Ga2O3 by NH3 whereby nitridation of β-Ga2O3 proceeds via the intermediate vapor species Ga2O(g). 相似文献
12.
Yusuke Himei Tomohiro Nagakane Naoyuki Kitamura Akihiko Sakamoto 《Journal of Non》2008,354(27):3113-3119
Reduction in the temperature coefficient of the optical path length, dS/dT of Li2O-Al2O3-SiO2 glass-ceramics with near-zero thermal expansion coefficient was attempted using control of the temperature coefficient of electronic polarizability, ?, and the thermal expansion coefficient, α. The dS/dT value of 2.6 mol% B2O3-doped glass-ceramic was 12.5 × 10−6/°C, which was 0.9 × 10−6/°C smaller than that of B2O3-free glass-ceramic. On the other hand, reduction in dS/dT through B2O3 doping was not confirmed in precursor glasses. Results showed that reduction in dS/dT of the glass-ceramic through B2O3 doping is caused by the reduction in ?. The reduction in ? from B2O3 doping was probably attributable to numerical reduction in non-bridging oxide ions with larger ? value by the concentration of boron ions in the residual glass phase. In addition, application of hydrostatic pressure during crystallization was effective to inhibit precipitation of β-spodumene solid solution, which thereby decreases dS/dT. The dS/dT value of B2O3-doped glass-ceramic crystallized under 196 MPa was 11.7 × 10−6/°C. That value was slightly larger than that of silica glass. The α value of this glass-ceramic was smaller than that of silica glass. 相似文献
13.
Utilizing P2O5 as nucleation agent, a Li2O-ZnO-Al2O3-SiO2 glass was prepared by conventional melt quenching technique and subsequently converted to glass-ceramics with different crystal phases. During the processing, two-step heat-treatments including nucleation and crystallization were adopted. The effects of heat-treatment on the crystal type, the microstructure and the thermal expansion behavior of the glass-ceramics were studied by means of differential scanning calorimetry, X-ray powder diffraction analysis, scanning electron microscopy and thermal expansion coefficient tests. It was shown that the crystallization of occurred after the glass was treated at 580 °C. As the temperature increased from 580 °C to 630 °C, cristobalite and were identified as main and second crystal phases, respectively, in the glass-ceramic. An increase in the temperature to 700 °C, the β-quartz solid solution in the glass-ceramic accompanied by a decrease in cristobalite content. The transformation from to γ0-Li2ZnSiO4 took place from 700 °C to 750 °C. The resulting crystallization phases in the glass-ceramics obtained at the temperature higher than 750 °C were β-quartz solid solution and γ0-Li2ZnSiO4. The glass-ceramics containing or β-quartz solid solution crystal phase possessed a microstructure formed by the development of dendritic crystals. The thermal expansion coefficient of the glass-ceramics varied from 36.7 to 123.8 × 10−7 °C−1 in the temperature range of 20-400 °C, this precise value is dependent on the type and the proportion of the crystalline phases presented. 相似文献
14.
Zengfeng Di Miao Zhang Weili Liu Suhua Luo Zhenghua An Zhengxuan Zhang Chenglu Lin 《Journal of Non》2005,351(1):93-96
Zr0.6Al0.4O1.8 dielectric films were deposited directly on strained SiGe substrates at room temperature by ultra-high vacuum electron-beam evaporation (UHV-EBE) and then annealed in N2 under various temperatures. X-ray diffraction (XRD) reveals that the onset crystallization temperature of the Zr0.6Al0.4O1.8 film is about 900 °C, 400 °C higher than that of pure ZrO2. The amorphous Zr0.6Al0.4O1.8 film with a physical thickness of ∼12 nm and an amorphous interfacial layer (IL) with a physical thickness of ∼3 nm have been observed by high-resolution transmission electron microscopy (HRTEM). In addition, it is demonstrated there is no undesirable amorphous phase separation during annealing at temperatures below and equal to 800 °C in the Zr0.6Al0.4O1.8 film. The chemical composition of the Zr0.6Al0.4O1.8 film has been studied using secondary ion mass spectroscopy (SIMS). 相似文献
15.
Xiaoyun Fan Shilie Pan Xueling Hou Xuelin Tian Jian Han 《Journal of Crystal Growth》2010,312(15):2263-2266
Colorless and transparent Na3VO2B6O11 (NVB) crystal has been grown by the top seeded solution growth method using NaVO3 as the flux at cooling rates of 0.8–1.5 °C/day, in the temperature range 610–650 °C. A well-developed morphology of the crystals was observed and analyzed. The grown crystals were characterized by powder X-ray diffraction (PXRD), infrared spectroscopy and second harmonic generation (SHG) test. 相似文献
16.
Sheikh Manjura Hoque A.K.M. Rezaul Haque N.H. Nghi Shireen Akhter 《Journal of Non》2011,357(10):2109-2114
We have prepared an amorphous Co68Fe4.5Sil2·5B15 alloy, annealed it in the temperature range of 200-580 °C and carried out a detailed study of the effect of crystallization on its magnetic properties. When annealed in an optimized condition, a very high value of initial permeability of the order of ~ 104 has been attained in association with a drastic decrease of the relative loss factor. This change of properties has been attributed due to the formation of nanograins of fcc Co and Co3B, as identified by X-ray diffraction and differential thermal analysis. The activation energy of crystallization is 4.18 eV. Hysteresis loop parameters were then extensively studied for the samples annealed at various temperatures. Finally, a very high value of giant magneto-impedance (GMI)—which is a characteristic property of Co-based amorphous alloys derived from well defined anisotropy axis (around 375) has been observed for a sample annealed at 380 °C. 相似文献
17.
In a melt with the base mol% composition 25Na2O-15B2O3-60SiO2, doped with chromium and manganese, a redox reaction takes place during cooling the melt. This reaction was studied using high temperature UV-vis spectroscopy. Above 600 °C, the reaction is in equilibrium and shifted during cooling to the Cr3+ and Mn3+ species. At temperatures between 500 and 600 °C, the kinetics of the redox reaction is decisive and the cooling rate plays an important part. At temperatures < 500 °C, the reaction is frozen in. The smaller the cooling rate, the smaller is the Cr6+ concentration and the lower is the fictive redox temperature.The kinetics of the reaction was described by a differential equation assuming Arrhenian behaviour. The equation was numerically solved and fictive temperatures were calculated. These temperatures depended on cooling rate similar to Bartenev equation. Activation energies calculated hereof were around 38 kJ?mol−1 larger than those inserted into the kinetic equation. The experimentally determined activation energy is 565 kJ?mol−1, a value much larger than the activation energies of diffusion of the polyvalent elements. The rate determining step in the case of the Cr3+/Cr6+/Mn2+/Mn3+ system is the electron transfer reaction, because a notable structural rearrangement is necessary during the course of the electron transfer reaction (Cr3+ and Cr6+ occur in octahedral and tetrahedral coordination, respectively). The latter leads to a large inner reorganisation energy and to an activation energy similar to that of the viscous flow. In the case of the redox reaction between copper and arsenic, the activation energy is much smaller (210 kJ?mol−1), because here the coordination numbers do not change during the course of the redox reaction. 相似文献
18.
New phosphate glasses of the quaternary system A2O-Nb2O5-WO3-P2O5, where X = Li and Na were prepared by the melt-quenching method. The introduction of WO3 in the glass composition was based on the proposal of analysing the effect of the diminishing of the molar amount of the alkaline oxide and thus decreasing the molar ratio between network modifiers and network formers (M/F).In the present work we present the preparation of 20A2O-30WO3-10Nb2O5-40P2O5 (A = Li, Na) transparent glasses. These glasses were heat-treated in air, at 550 °C and 650 °C for 4 h. The structure of the obtained samples was studied by X-ray powder diffraction (XRD) and Raman spectroscopy and the morphology by scanning electron microscopy (SEM). The dc (σdc), ac (σac) conductivity and dielectric spectroscopy measurements were performed in the function of the temperature and were related with the structural changes of the glass structures. 相似文献
19.
In this study, we have investigated the effect of substituting Mn for Fe on the crystallization kinetics of amorphous Fe73.5−xMnxCu1Nb3Si13.5B9 (x = 1, 3, 5, 7) alloys. The samples were annealed at 550 °C and 600 °C for 1 h under an argon atmosphere. The X-ray diffraction analyses showed only a crystalline peak belonging to the α-Fe(Si) phase, with the grain size ranging from 12.2 nm for x = 0 to 16.7 nm for x = 7. The activation energies of the alloys were calculated using Kissinger, Ozawa and Augis-Bennett models based on differential thermal analysis data. The Avrami exponent n was calculated from the Johnson-Mehl-Avrami equation. The activation energy increased up to x = 3, then decreased with increasing Mn content. The values of the Avrami exponent showed that the crystallization is typical diffusion-controlled three-dimensional growth at a constant nucleation rate. 相似文献
20.
Kaupo Kukli Mikko RitalaMarkku Leskelä Timo SajavaaraJuhani Keinonen David GilmerSandeep Bagchi Lata Prabhu 《Journal of Non》2002,303(1):35-39
Ta2O5, Ta-Nb-O, Zr-Al-Nb-O, and Zr-Al-O mixture films or solid solutions were grown on Si(1 0 0) substrates at 300 °C by atomic layer deposition. The equivalent oxide thickness of Ta2O5 based capacitors was between 1 and 3 nm. In Zr-Al-O films, the high permittivity of ZrO2 was combined with high resistivity of Al2O3 layers. The permittivity, surface roughness and interface charge density increased with the Zr content and the equivalent oxide thickness was between 2.0 and 2.5 nm. In the Zr-Al-Nb-O films the equivalent oxide thickness remained at 1.8-2.0 nm. 相似文献