摘要:

Heavy‐metal oxide glasses might arbitrarily be defined as those containing over 50 cation percent of bismuth and lead which participate in the glass structure as network formers. Glass systems based on these heavy‐metal oxides in silicates, borates, phosphates, germanates, and ferrites are surveyed. Gallate systems are emphasized since they have a unique ability to form stable glasses while maintaining key properties, such as the best infrared transmission and the highest nonlinear optical susceptibilities and diamagnetic Verdet constants for oxide glas

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05581.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A model has been developed for creep due to viscous flow in a material containing a non‐Newtonian, amorphous grain boundary phase. The model describes the process whereby glass is squeezed out from between grain boundary layers in compression, and flows toward grain boundary layers under tension. A pseudo steady state, in which the creep rate is constant, is seen at small strains. However, beyond a critical strain, the strain rate starts to decrease rapidly, and no creep is possible once adjacent grains come into contact. The maximum possible strain is twice as large in tension as in compression. This leads to a form of anisotropy which may explain the shift in neutral axis which occurs during flexural cree

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05582.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Amorphous films in the system AlPO4–TiO2were prepared by an rf‐sputtering method, and their physical properties, such as density, refractive index, and thermal expansion coefficient, and the infrared absorption spectra were measured. The thermal expansion coefficient increased linearly with increasing TiO2content. The results of the molar refractivity and the infrared absorption spectra indicated that the coordination number of titanium ions in these films is higher than that in SiO2–TiO2glasses with a negative thermal expansion, in which Ti4+ions are tetrahedrally coordinated. In order to confirm the coordination state of the titanium ions in these amorphous films, titaniumK‐band emission spectra were obtained by X‐ray emission spectroscopy, revealing sixfold coordination. The higher coordination state of Ti4+was considered to account for these amorphous films not exhibiting negative thermal expansion, as in the SiO2

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05583.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

An ongoing challenge for future developments in high‐performance ceramic multilayer capacitors and integrated ceramics is to reduce the internal electrode cost and thickness without sacrificing yield or reliability. Key to these developments is a thorough understanding of the interactions which occur between flux‐sintered dielectrics and low‐cost, Ag/Pd electrodes. In this paper we present results on the pahse equilibria of Ag/Pd electrode systems with Bi2O3and PbO fluxes. The conditions under which the bismuth reaction occurs and reactions in the Pd–PbO system are reported. Results show that the equilibrium phases which form depend strongly upon the Ag/Pd ratio and temperature. These phases include PdBi2O4, Pd(Bi), PdPbO2, Pd(Pb), and PbPd3. The PdBi2O4and PdPbO2phases decompose when PdO destabilizes, resulting in a series of reactions which result in oxygen evolution and partial melting of components. The exact phase relations of the Ag/Pd–Bi2O3–O2(air) system and Ag/Pd–PbO–O2(air) system have been established for the first time and are discussed in terms of their impact on multilayer, cof

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05584.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Sodium aluminosilicate (NAS) glass surfaces with compositions containing approximately 63% SiO2and Al/Na ratios,R, of 0.25R2.0 were simulated using the molecular dynamics technique with a multibody interaction potential. There were changes to the surface structure and composition in comparison to bulk NAS glasses. The changes included an increased concentration of sodium and oxygen and the formation of nonbridging oxygen at the outermost surfaces, although the increases were smaller with increased Al concentration. In addition, the formation of small‐membered rings and three‐coordinated aluminum occurred in the subsurface regions. These changes were accompanied by a change in the ratio of Al/Na in the region extending to 4 Å below the sur

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05585.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Si3N4/SiC composites are ceramic materials that exhibit excellent performance for high‐temperature applications. Prepared from an ultrafine amorphous Si‐C‐N powder, sintered materials are constituted mainly of aβ‐Si3N4matrix with SiC inclusions and have a very small grain size (less than 1 μm). Such a microstructure is propitious for superplastic forming. Superplasticity has been studied in tension, from 1550° to 1650°C, under nitrogen atmosphere. Elongations over 100% have been achieved. In many cases, at the highest temperatures and slowest strain rates, materials are damaged by different processes, including microcracking, cavitation, and chemical decomposition. A map of the most suitable (strain‐rate/temperature) domain has been established. It allows the prevention of any structural alteration by selecting carefully the testing conditions. Since specimens suffered considerable strain‐induced hardening, sources for this phenomenon are examined. Although the experiments have involved high temperature and extensive strain, neither static nor dynamic grain growth has occurred. Crystallization of the amorphous grain‐boundary phase, which is reported in most cases, may be invoked. However, based on microstructural observations, it is not the unique origin f

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05586.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

A simple test to predict linear shrinkage of tape‐cast green sheets as a function of time was developed. Shrinkage was found to correlate inversely with the amount of organic phase bound to ceramic particle surfaces. The test was developed for alumina green tapes with acrylic binder. The correlation was found to be independent of the medium used for the two slurry systems evaluated, water and toluene/ethanol. Treatments developed to dimensionally stabilize green sheets reduced shrinkage after 35 days of aging to less than 0.15%. Stabilization treatments involved heating and/or polymer swelling which facilitated the binding of organic phase to alumina particles, causing the tape to be in a more relaxed stat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05587.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

Using a linear voltage ramp method, ultraslow dielectric relaxation processes of La‐doped BaTiO3boundary layer (BL) capacitors are measured at room temperature. For the electric polarization model of a double‐layer dielectric, a procedure to calculate the electrical parameters of grain and grain boundary has been developed. Calculated results suggest that there is a shell on the surface of the grain. TEM images of the BL capacitor also show a lot of microregions with minor structural modifications. Relaxation times are estimated from the equivalent circuit and are in agreement with fitted resu

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05588.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The influence of the initial grain morphology on the anomalous grain growth in donor‐doped barium titanate has been studied. The results show that powders with aspherically shaped grains exhibit a much lower critical donor‐dopant concentration, inhibiting anomalous grain growth during sintering, than powders with equisized spherically shaped grains and a similar, or even a lower, initial specific surface a

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05589.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

The superconducting properties of a solid‐solution region in the Ba‐Y‐Gd‐Cu‐O system were investigated as a function of composition. Phase relations, the peritectic decomposition temperature, the superconducting onset temperature (Tc), and the transport current density (Jc) were measured. The highestTcandJcare observed along the line between the stoichiometric Ba2YCu3O6+xand Ba2GdCu3O6+xcom

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1992.tb05590.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY