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排序方式: 共有105条查询结果,搜索用时 15 毫秒
41.
M.A. Cortés-Jácome J.A. Toledo-AntonioH. Armendáriz I. HernándezX. Bokhimi 《Journal of solid state chemistry》2002,164(2):339-344
Catalysts in the WO3-ZrO2 system were produced by coprecipitation of aqueous solutions of zirconium oxynitrate and ammonium metatungstate. Samples were characterized by X-ray powder diffraction, thermogravimetry, and refinement of their crystalline structures with the Rietveld method. This coprecipitation gave rise to solid solutions of tungsten oxide into zirconia; the initial phase was amorphous and crystallized into two tetragonal crystalline phases, T1 and T2, when samples were annealed at 560°C. The main difference between both phases was the oxygen position along the c axis. In the phase with higher symmetry, T2, an oxygen atom was at one-half of the unit cell, 0.50(2), producing flat crystallite surfaces perpendicular to the c axis, while in the phase with the lower symmetry, T1, it was at 0.447(2), and gave rise to rough crystallite surfaces parallel to (100) planes. The interpenetrating tetrahedra forming the representative polyhedron of the crystalline structure were almost nondeformed in the phase with higher symmetry, because all Zr-O atom bond lengths were very similar. As the annealing temperature of the sample was increased, the dissolved tungsten atoms in the phase with higher symmetry segregated to the crystallite's surface. 相似文献
42.
C. A. Kawaguti L. A. Chiavacci S. H. Pulcinelli C. V. Santilli V. Briois 《Journal of Sol-Gel Science and Technology》2004,32(1-3):91-97
This paper describes the effect of sulfate, phosphate and nitrate complexing ligands on the structural features of amorphous xerogels and on the crystallization of metastable zirconia phases during the xerogel-ceramic conversion. Powdered samples were prepared by a sol–gel route using zirconyl chloride precursors chemically modified by complexing ligands. The structural evolution of ZrO2 phases as function of firing temperature was analyzed by XRPD, EXAFS and 31P NMR/MAS. The experimental results show the formation of metastable t-ZrO2 during the low firing temperature of xerogels modified by sulfate or phosphate groups. The martensitic tetragonal-monoclinic transformation occurs during desorption of sulfate groups. The largest temperature interval of stability of metastable tetragonal zirconia was observed for phosphate-modified xerogels. 相似文献
43.
Single crystals of a novel ScB19 family compound ScB19+xSiy were grown by the floating zone method using a four-lamp mirror-type image furnace. A small amount of silicon addition to ScB19 which decomposes at elevated temperatures without melting allowed it to coexist with the liquid phase and as a resultant made the floating zone crystal growth possible. Powder X-ray diffraction analysis confirmed the grown crystals of ScB19+xSiy to be isostructural to ScB19. It was found that the crystal structure of ScB19+xSiy solved based on single-crystal X-ray data is tetragonal with lattice constants of a, b=1.03081(2) nm, c=1.42589(3) nm, space group P41212 or P43212 and is basically isotypic with α-AlB12 structure type. In the crystal structure boron atoms form a three-dimensional framework based on interconnected B12 icosahedra and B22 polyhedra. The Sc atoms reside in three of five Al sites in the α-AlB12 structure and Si resides in a bridge site bonding two B22 units. 相似文献
44.
运用密度泛函平面波赝势(PWP)和广义梯度近似(GGA)方法,对二氧化钒(VO2)两种不同晶体电子结构进行了计算.研究了低温单斜晶型和高温四方晶型结构的VO2电子态密度(DOS)和能带(energyband)结构,通过分析发现,四方晶的金属性比较明显,这是由于电子态密度和能带结构分析结果表明不同特性产生的原因是V原子的3d电子贡献不同导致的.本文中我们还将部分O原子替换为F原子后对单斜晶替位掺杂进行了的计算讨论,本文的计算结果都较好地符合实验结果,表明密度泛函平面波赝势和广义梯度近似方法可以用来描述VO2的结构和性质.我们认为,这种方法应用于描述氧化物的电子结构和性质是一种新的探索. 相似文献
45.
Satoru Utsugi Yoshitaka Ehara Hidenori Tanaka Tomoaki Yamada Hiroshi Funakubo Hiroshi Uchida 《Journal of Crystal Growth》2010,312(21):3127-3130
Epitaxial (La0.07Sr0.93)SnO3 [LSSO] films were deposited on CaF2 substrates by pulse laser deposition. The (1 0 0)c orientation of LSSO films was observed only on (1 1 0)CaF2, whereas (1 1 0)c orientation was found on (1 1 1)CaF2 and (1 0 0)CaF2. (0 0 1) polar axis oriented tetragonal Pb(Zr0.35Ti0.65)O3 films were grown on the fabricated (1 0 0)cLSSO∥(1 1 0)CaF2 by pulsed metal organic chemical vapor deposition. The (0 0 1)Pb(Zr0.35Ti0.65)O3∥(1 0 0)cLSSO∥(1 1 0)CaF2 stack structure exhibited about 70% transparency with an adsorption edge of approximately 330 nm. 相似文献
46.
Electric field gradient (efg) is calculated at the centre of the cell in the simple tetragonal crystal. The method uses Euler-Maclaurin summation formula
and makes the planewise summation in the direct crystal space without any special regrouping of charges in point charge model.
The results are in fair agreement with previous results of de Wette on the same system using Fourier transform to reciprocal
space. 相似文献
47.
The tripodal ligand N,N′,N″-tri(benzimidazolyl)-methane has been used to synthesize nickel(II) complexes along with an exogeneous
ligand, X(X = Cr−,NO
3
−
,ClO
4
−
, HCOO−, OAc− and CNS−). Electronic absorption spectra reveal that the present nickel(II) complexes have six coordinate tetragonal geometries. The
value of Racah parameter(B), crystal field splitting parameter (Dq) and term,β0 (which is a measure of covalency) have been calculated.1HNMR spectroscopy reveals a dominantσ-delocalization pattern in these complexes. 相似文献
48.
O. Saligheh R. Khajavi M. E. Yazdanshenas A. Rashidi 《Journal of Macromolecular Science: Physics》2016,55(6):605-616
Zirconia (ZrO2) inorganic ceramic nanofibers were produced using electrospinning of the poly(vinyl alcohol)/zirconium acetate as a precursor followed by calcinating and sintering to decompose the polymer and turn the metal salt (zirconium acetate) into the metal oxide. Characterization of the nanofibers, including polymer thermal decomposition, chemical and crystal structure, phase transformations, and fiber morphology were investigated by simultaneous thermal analysis (STA), thermomechanical analysis (TMA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), and field emission scanning electron microscopy (FESEM). The results showed that the polymer decomposition started at 250°C and zirconia nanofibers with different phases (tetragonal and monoclinic) were obtained by the calcination of the precursor nanofibers at various temperatures between 500°C and 1100°C. The initially crystallized zirconia phase, which formed at 500°C, was tetragonal and with increasing calcination temperature, zirconia nanofibers with increasing amount of monoclinic phase were formed. Consequently, at 1100°C, the tetragonal phase disappeared and was transformed to the monoclinic phase of the zirconia completely. Increasing the calcination temperature caused the fiber average diameter decrease and grain growth took place due to the removal of the polymer and organic groups; neighboring grains sintered to each other and formed fibers with a high aspect ratio. At 1100°C the grains size was about the same as the fiber diameter. 相似文献
49.
Angelica Garzon‐Fontecha Harvi A. Castillo Mario Curiel Ana Gabriela Montao‐Figueroa Manuel A. Quevedo‐Lopez Leonel Cota‐Araiza Wencel De La Cruz 《Surface and interface analysis : SIA》2021,53(1):68-75
Tin oxide (SnOx) has been widely used for the fabrication of transparent and flexible devices because of its excellent optical and electronic properties. In this work, we established a methodology for the synthesis of SnOx thin films with p‐type and n‐type tunable conductivity by direct currecnt (DC) magnetron sputtering. The SnOx thin films changed from p‐type to n‐type by increasing the relative oxygen partial pressure (ppO2) from 4.8% to 18.5% and by varying the working pressure between 1.8 and 2.5 mTorr. The SnOx thin films were annealed at 160°C, 180°C, and 200°C for 30 min to promote the formation of the desired crystalline structures. At the annealing temperature of 180°C in air ambient, the SnOx thin films showed a tetragonal structure with Sn traces. Having found the optimal conditions, we deposited both types of SnOx thin films with the same tetragonal structure and similar chemical stoichiometry. Also, the conditions to obtain thin films with the highest mobility values for p‐type (1.10 cm2/Vs) and n‐type (22.20 cm2/Vs) were used for fabricating the device. Finally, the implementation of a SnOx‐based p–n diode was demonstrated using transparent SnOx thin films developed in this work, illustrating their potential use in transparent electronics. 相似文献
50.
以钛酸四丁酯和硝酸钡为主要原料,采用微波辅助草酸盐沉淀法制备了纯度高、结晶度较好的四方相钛酸钡纳米粉体.分别采用X射线衍射分析(XRD)、扫描电子显微镜(SEM)和透射电子显微镜(TEM)对钛酸钡纳米粉体的结构、粒径及形貌进行表征.结果表明,在钡/钛摩尔比为1,微波温度80 ℃、微波时间30 min,煅烧温度700 ℃,煅烧时间1 h,通过添加表面活性剂OP-10,制备出粒径在50 nm左右且四方度为1.0069的钛酸钡纳米粉体,其中微波合成温度及合成时间对钛酸钡纳米粉体的四方度的影响较大. 相似文献