摘要:

The sol–gel process has been applied to the preparation of small‐sized CdTe‐doped silica glasses. Gels synthesized by the hydrolysis of a complex solution of Si(OC2H5)4, Cd(CH3COO)2· 2H2O, and Te were heated from 350° to 600°C in a H2─N2atmosphere to form fine cubic CdTe crystals. The size of CdTe crystals, determined from the line broadening of X‐ray diffraction pattern, increases from 4 to 9 nm in diameter with increasing heat‐treatment temperature. The optical absorption edge shifts to the higher‐energy side as the size of the CdTe crystals decreases. This phenomenon is interpreted in terms of a quantum confinement effect of electron and hole in the Cd

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05471.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

X‐ray diffraction studies have been used to follow the formation of Al4SiC4from Al4C3and SiC and the role played by impurity oxygen. The phase Al2OC forms in the early stages of reaction and reacts with SiC at ≈ 1700°C to produce Al4SiC4plus a small amount of an aluminosilicate liquid. This liquid dissociates at higher temperatures, the resulting evolution of gases hindering complete densification. Higher densities are obtained on hot‐pr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05472.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The structure of mullite was refined by the Rietveld method, and a new method for the estimation of chemical composition of mullite was proposed. Mullites were synthesized by firing the starting materials prepared by sol–gel and spray pyrolysis methods at various temperatures. Linear correlations were recongnized between the chemical composition of mullite analyzed with the Rietveld method and the lengths ofaandbaxes, but a small anomaly was found in the variation of thecaxis. It was found to be caused by a difference in thecaxis of pseudotetragonal mullite and that of orthorhombic mullite. A good correlation was found between the chemical composition of mullite and the intensity ratio of (I220/I111). This is a much more convenient method for estimating the chemical composition of mullite than Cameron's method, which uses a lattice constan

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05473.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Metal‐doped superconductor thick films Bi1.6Pb0.4M0.1Ca2‐Sr2Cu3Ox(M = V, Nb, Mo, In, Sn, Sb, and W) were prepared using a melt–solidification procedure. The optimum heat‐treatment temperatureToptwas observed in all the films with different dopants;Toptwas related to the temperature at which a partial melting of the films occurred as determined by differential thermal analysis. The dopants in the melt‐solidified films lower the partial melting temperature and thus lowerToptfor the formation of the 11

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05474.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A complex perovskite of Sr(CuxZn1‐x)1/2W1/2O3(SCZW) is synthesized by a new combination of wet and dry processess. Mixed oxides containing Cu2+and Zn2+(CZ) are prepared by the wet process (coprecipitate method). SCZW is obtained by the dry process (mixed‐oxide method) from a mixture of CZ, SrCO3, and WO3. SCZW has practically no compositional, unlike solid solutions prepared by the conventional dry method. The wet–dry process method is useful because the wet process is applied to only B‐site cations having the same

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05475.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Silicon carbide (SiC) containing He atoms expands by annealing above ∼ 1300°C, owing to the formation and growth of He bubbles. An external compressive stress applied during annealing retards expansion in the stress direction, while promoting it in the lateral directions. It is proposed that He atoms in the bubbles on grain boundaries perpendicular to the compression axis are transported to the bubbles on boundaries parallel to the stress axis. The transport of He accompanies changes in the volumes of the bubbles to maintain equal pressure in all the bubbles. The volume changes of the bubbles are caused by the flow of SiC‐constituting atoms from or to the boundaries where the volume‐changing bubbles exist. This process results in a jacking action which alters the thickness of boundary atom layers. It produces macroscopic strains. The plausibility of the proposed process is examined on the basis of ener

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05476.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Cubic boron nitride (c‐BN) was synthesized by the decomposition of Mg3BN3under high pressure and high temperature. The minimum pressure forc‐BN synthesis was 4 GPa, which was 1 GPa lower than that of the conventional catalytic process. The decomposition of Mg3BN3was observed only when H2O was added. Therefore, the reaction was as follows: Mg3BN3+ 3H2O = 3MgO +c‐BN + 2NH3. Thec‐BN crystals obtained were tetrahedron in shape and about 10μm in

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05477.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Titanium nitride ultrafine powders were synthesized by an active plasma‐metal reaction method. Gas desorption measurements were conducted to estimate the surface chemistry of the powders after exposure to air and storage at room temperature. H2O, H2, CO2, CO, and NH3gases were mainly evolved. These gases were considered to be formed by the surface reaction of adsorbed gases on surface oxide of the powders and decomposition of hydroxide‐like or ammonialike compounds, which might be produced during a slow oxidation treatment and stor

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05478.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A SiAlON ceramic with yttria as a sintering aid has been fabricated and subjected to a 1‐h heat treatment at 1150°C. Microstructural characterization by analytical electron microscopy and diffraction analysis indicates that the residual intergranular phase crystallizes into a metastable hexagonal phase (Y2SiAlO5N) and mullite. The mullite appears as a characteristically shaped precipitate forming with a definite orientation relationship on the (1010) facets of SiAlON grains. The absence of a residual amorphous film between the precipitate and the SiAlON indicates that the precipitation occurred in a heterogeneous manner on the surface of the SiAl

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05479.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Transmission electron microscopy clearly demonstrates two types of grain boundaries in a shock‐consolidated diamond compact consisting of fine particles: one is thick (40 nm) and irregular, whereas the other is thin (less than a few nanometers) and straight. The former is formed during the first compression (21 GPa) while the latter is formed after passage of the first shock‐wave front. Numerical calculations describing thermal diffusion support the proposed mechanism under a multiple‐compression pr

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05480.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY