Good Crystallinity (good + crystallinity)

Distribution by Scientific Domains

Selected Abstracts

Preparation of LiMn2O4 powders via spray pyrolysis and fluidized bed hybrid system

AICHE JOURNAL, Issue 7 2006
Izumi Taniguchi
Abstract A novel technique has been developed to directly produce fine ceramic powders from liquid solution using a spray pyrolysis and fluidized bed hybrid system. Using this technique, the preparation of lithium manganese oxides LiMn2O4, which are the most promising cathode materials for lithium-ion batteries, has been carried out for various superficial gas velocities U0 = 0.30-0.91 m/s, static bed heights Ls = 50-150 mm, and medium particle sizes dpm,g = 294-498 ,m. The resulting powders had spherical nanostructured particles that comprised primary particles with a few tens of nanometer in size, and they exhibited a pure cubic spinel structure without any impurities in the XRD patterns. Moreover, the as-prepared powders showed better crystallinity and smaller specific surface area than those by conventional spray pyrolysis. The effects of process parameters on powder properties, such as specific surface area and crystallinity, were investigated for a wide range of superficial gas velocities and static bed heights. An as-prepared sample was used as cathode active materials for lithium-ion batteries and the cell performance has been investigated. Test experiments in the electrochemical cell Li/1M LiClO4 in PC/LiMn2O4 demonstrated that the sample prepared by the present technique was superior to that by the conventional spray pyrolysis and solid-state reaction method. 2006 American Institute of Chemical Engineers AIChE J, 2006 [source]

Direct Synthesis of New Zircon-Type ZrGeO4 and Zr(Ge,Si)O4 Solid Solutions

Masanori Hirano
A new phase of ZrGeO4 was hydrothermally synthesized from a mixture of ZrOCl2 solution and GeO2 powder at 240C. X-ray diffractometry patterns of synthesized ZrGeO4 particles, which had better crystallinity than ZrSiO4 particles prepared by the same process from ZrOCl2 and tetraethoxysilane, could be indexed for a zircon-type tetragonal structure, having a0= 0.6694(0) and c0= 0.6265(7) nm. The c/a ratio of synthesized ZrGeO4 (0.9360) was larger than that of ZrSiO4 (0.9054). Solid solutions with zircon-type structure over the whole composition range in the ZrGeO4 -ZiSiO4 system were also directly synthesized through the same solution route. The secondary particle size of zircon-type Zr(Ge,Si)O4 solid solutions decreased, and its morphology gradually changed from octahedron-like to blood-red cell-like with decreased GeO2 content. [source]

Copolyesters of hydroxyphenylalkanoic acids: synthesis and thermal properties of poly{(4-oxybenzoate)- co -[8-(3-oxyphenyl)octanoate]} and poly{(3-bromo-4-oxybenzoate)- co -[8-(3-oxyphenyl)octanoate]}

Shiney Abraham
Abstract Copolyesters of 8-(3-hydroxyphenyl)octanoic acid (HPOA), a monomer with kink and flexible segment derived from cardanol, and 4-hydroxybenzoic acid (HBA) or its brominated derivative, 3-bromo-4-hydroxybenzoic acid (BrHBA), were synthesized by acidolysis melt polycondensation of the in situ generated acetoxyderivative in the presence of magnesium acetate as catalyst by a one-pot method and characterized. The formation of the copolyester was confirmed by elemental analysis, FTIR and 1H NMR spectroscopy. These polymers were highly insoluble in most solvents except highly polar solvents, such as trifluoroacetic acid. The inherent viscosities of the soluble polymers were in the range of 0.8,1.1,dlg,1. The thermal and phase behaviour of the copolyesters were studied by DSC and polarized light microscopy. Poly{(4-oxybenzoate)- co -[8-(3-oxyphenyl)octanoate]} with 50 mole% of HPOA showed a birefringent melt with opalescence and a worm-like texture of a nematic phase. The effect of bromine substitution in the analogue poly{(3-bromo-4-oxybenzoate)- co -[8-(3-oxyphenyl)octanoate]} was evident when it showed a lower transition with minimum 45% Br-HBA at 225,C showing enhanced melt processability. These copolymers, with hydrolytically degradable aliphatic carbonyl group and better crystallinity compared to poly(hydroxyalkanoate)s, are interesting in possible biomedical applications. 2002 Society of Chemical Industry [source]

Nanocrystalline transparent SnO2 -ZnO films fabricated at lower substrate temperature using a low-cost and simplified spray technique

K. Ravichandran
Abstract Nanocrystalline and transparent conducting SnO2 - ZnO films were fabricated by employing an inexpensive, simplified spray technique using a perfume atomizer at relatively low substrate temperature (3605 C) compared with conventional spray method. The structural studies reveal that the SnO2 -ZnO films are polycrystalline in nature with preferential orientation along the (101) plane. The dislocation density is very low (1.481015lines/m2), indicating the good crystallinity of the films. The crystallite size of the films was found to be in the range of 26,34 nm. The optical transmittance in the visible range and the optical band gap are 85% and 3.6 eV respectively. The sheet resistance increases from 8.74 k,/, to 32.4 k,/, as the zinc concentration increases from 0 to 40 at.%. The films were found to have desirable figure of merit (1.6310,2 (,/,),1), low temperature coefficient of resistance (,1.191/K) and good thermal stability. This simplified spray technique may be considered as a promising alternative to conventional spray for the massive production of economic SnO2 - ZnO films for solar cells, sensors and opto-electronic applications. ( 2010 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Effect of AlN doping on the growth morphology of SiC

N. B. Singh
Abstract AlN doped SiC films were deposited on on-axis Si-face 4H-SiC (0001) substrates by the physical vapor transport (PVT) method. Thick film in the range of 20 ,m range was grown and morphology was characterized. Films were grown by physical vapor deposition (PVD) in a vertical geometry in the nitrogen atmosphere. We observed that nucleation occurred in the form of discs and growth occurred in hexagonal geometry. The X-ray studies showed (001) orientation and full width of half maxima (FWHM) was less than 0.1 indicating good crystallinity. We also observed that film deposited on the carbon crucible had long needles with anisotropic growth very similar to that of pure AlN. Some of the needles grew up to sizes of 200 ,m in length and 40 to 50 ,m in width. It is clear that annealing of SiC-AlN powder or high temperature physical vapor deposition produces similar crystal structure for producing AlN-SiC solid solution. SEM studies indicated that facetted hexagons grew on the top of each other and coarsened and merged to form cm size grains on the substrate. ( 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim) [source]

Highly Crystalline, Idiomorphic Na2Ti6O13 Whiskers Grown from a NaCl Flux at a Relatively Low Temperature

Katsuya Teshima
Abstract Well-developed, highly crystalline Na2Ti6O13 whiskers were successfully grown by cooling a NaCl flux at a relatively low temperature of 700 C. The obtained Na2Ti6O13 whiskers were colorless and transparent. The whiskers grown at 700 C were single phase and exhibit the lowest sizes of up to about 3.5 ,m,,0.1 ,m. From the results of SEM, XRD, and TEM, it was confirmed that the Na2Ti6O13 whiskers have very good crystallinity and elongated in the [lang]010[rang] directions. Furthermore, the whiskers exhibited good photocatalytic activity under ultraviolet light irradiation. It is reasonable to suppose that NaCl can be adequately used to synthesize high quality and well-developed titanate whiskers in an environmentally friendly process of crystal growth. [source]

The effect of oxygen on interface microstructure evolution in CdS/CdTe solar cells

D.S. Albin
Microstructural changes at the CdS/CdTe solar cell interface where close-spaced sublimation (CSS) is used as the growth technique to deposit the p -type CdTe absorber layer are studied by systematic layer characterization at various stages during heterojunction growth. CdS layers grown by both chemical bath deposition (CBD) and CSS provide a basis for determining the effects of CdS crystallinity, grain size, and oxygen content on the subsequent CdTe layer. As-grown CBD CdS films exhibit small grains and variations in optical properties attributed to film impurities. In contrast, CSS yields CdS films with good crystallinity, larger grains, and nearly ideal optical properties. The hexagonal nature of CSS-grown CdS is seen to nucleate hexagonal CdTe during the initial stages of CdTe film growth. Cubic CdS deposited by CBD in contrast promotes cubic CdTe nucleation. Oxygen anneals in the latter case can aid hexagonal CdTe nucleation. Auger electron spectroscopy (AES) and transmission electron microscopy (TEM) of the CdS/CdTe interface show CdS-dependent differences in interdiffusion at the interface. This interdiffusion appears to be determined by the oxygen level in the CdS. When low-oxygen-containing CSS CdS films are used, sulfur diffusion is substantial, leading to significant consumption of the CdS layer. When these same films are annealed in oxygen, the consumption is reduced. Te diffusion into the CdS layer is also observed to decrease with oxygen anneals. Optical modeling shows that Te alloying with the CdS layer can greatly reduce the short-circuit current of CdS/CdTe devices. Copyright 2002 John Wiley & Sons, Ltd. [source]