摘要:

Optical and DTA measurements of a single crystal of LiNbO3pulled from the congruent melt indicate a radial composition gradient leading to a Li‐rich surface. From Tcmeasurements it is concluded that the surface is ≥0.15 mol% Li2O richer than the bulk composition. The skin thickness is ≤1 mm and is generally removed prior to device preparation; however, some possible sources of concern are discussed for subsequent high‐temperature pro

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06392.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Several experiments were conducted to investigate the formation mechanisms of the magnetoplumbite phase in La3+‐doped CaO 6Fe2O3. It is shown that the CaO·2Fe2O3phase plays a crucial role in forming the magnetoplumbite phase. The formation mechanisms are proposed and verifi

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06393.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Hardness was measured as a function of temperature (20° to 1000°C) for several Al2O3ceramics, including single‐crystal sapphire and polycrystalline aluminas containing different amounts of second phase. Hardness decreased steadily with increasing temperature for all materials tested, in accordance with a semiempirical relation of the form H=H0(1 – T/T0). This behavior conformed with a thermally activated slip process, limited by Peierls stresses. At lower temperatures, the hardness values for debased aluminas were less (smaller H0) than for the pure materials, consistent with a reduction in shear modulus resulting from the “soft” phase. However, at higher temperatures the hardness values for all the aluminas converged (identical T0, i.e., material‐invariant activation energy). The latter behavior indicated that the temperature dependence of the indentation deformation was controlled predominantly by the Al2

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06394.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Decomposition of Mg(OH)2at 300° to 400°C yields MgO crystals with often unequal edge lengths which, from counting of crystal planes in high‐resolution transmission electron micrographs, range from 0.8 to 2.4 nm, in agreement with conclusions of Moodie and Warble. Optical diffractograms and electron diffraction patterns yield concordant results. An origin for discordant X‐ray diffraction estimates of particle size for MgO produced from Mg(OH)2in the same temperature range is sugg

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06395.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The experimental performance of the Shelyubskii method has been improved and applied to studying the change in glass homogeneity of the system Li2O‐SiO2caused by phase separation. Binodal temperatures obtained by this method are in good agreement with literature data obtained by an alternative method. The Shelyubskii method is capable of monitoring changes in glass homogeneity from a change in refractive index of the material with an accuracy of Δn×1

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06396.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A metastable modification of Y2TeO6crystallizes at 770°C to 870°C at a heating rate of 10°C·min−1in air from an amorphous material prepared by the simultaneous hydrolysis of yttrium and tellurium alkoxides. It has a tetragonal unit cell with a=1.0428 nm and c=1.7524 nm. The tetragonal‐to‐hexagonal phase transformation occurs at 920° to 960°C. Hexagonal Y2TeO6decomposes into Y6TeO12and TeO3↑ at 1220° to 1320°C; only Y6TeO12is obtained as the decomposition product. Both modifications of Y2TeO6are built up by octahe

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06397.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

The densification behavior of Al2O3‐MgO (0.1 wt%) has been studied in O2and N2atmospheres. Powder compacts have been sintered at 1600°C for 0.5 to 8 h. For some specimens the sintering atmosphere has been changed after 30 min of sintering. Irrespective of sintering atmosphere, sintered densities are approximately the same up to 99% relative density, implying that the capillary pressure effect dominates the atmosphere effect for most of the densification stage. During extended sintering treatment the density of specimens sintered in O2becomes higher than that in N2. When the sintering atmosphere is changed from O2to N2, enhanced densification results, and vice versa. Such an effect of sintering atmosphere is explained by the diffusiveness of gases entrapped in pores, as well as by oxygen potential differences inside and outside of the specimen. Differences in grain growth rate in various atmospheres are discussed on the basis of different densification rat

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06398.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

Structural changes of 2.5‐mol%‐Y2O3‐stabilized tetragonal ZrO2polycrystal fractured surfaces, as well as ground, polished, and annealed surfaces, were studied by X‐ray diffraction. Much greater intensity of the (200) tetragonal peak than (002) was found on the thin surface layer of the ground specimen, but not on the fracture surface. The intensity changes were discussed in relation to the toughening me

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06399.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

A recently reported method has been used to propagate stable mixed mode I‐mode III cracks in thin slices of single‐crystal α‐quartz (low quartz, SiO2) and single‐crystal rutile (TiO2). A bond‐counting technique has been developed and used to isolate planes of weakness in the crystalline structures of both crystals. Good correlation has been obtained with observed crack planes. Mode III component (KIII) versus crack velocity (v) relations for specified mode I contributions have thus been determined form{1010} fracture in basal (0001) slabs and for {a+c} fracture inm{1010} slabs of α‐quartz and also for (110) fracture in basal (001) and (101) fracture in (010) sl

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06400.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY

摘要:

This communication demonstrates an application for computer simulation techniques to determine the energies of perfect surfaces and of defects near those surfaces. The work presented here will concentrate on Cr2O3, determining the perfect surface energies of five low‐index planes and the vacancy formation energies as a function of distance from the two lowest‐energy pla

ISSN:0002-7820    

DOI:10.1111/j.1151-2916.1988.tb06401.x

出版商:Blackwell Publishing Ltd    

年代:1988

数据来源: WILEY