摘要:

Using a recently developed specimen-preparation technique to examine heteroepitactic growth in ceramics, the early development of grain orientation in thin YBa2Cu3O7-δfilms prepared by pulsed-laser ablation can be determined. The technique involves deposition directly on to a specially prepared electron-transparent substrate. The films are examined during the early stages of growth by transmission electron microscopy. Three different orientations corresponding to different alignments of thecaxis of the YBa2Cu3O7-delta; unit cell with the MgO substrate could be determined from the particle morphology in the image, but were not detected by selected-area diffraction due to their small size.

ISSN:0950-0839    

DOI:10.1080/09500839008203742

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Aluminium nitride polycrystals have been irradiated to fluences up to 5·2 × 1024neutrons m-2(E > 1·0 MeV) in a thermal-fast mixed reactor, the JMTR. Dislocations induced by the neutron irradiation were studied by high-resolution electron microscopy coupled with a multi-slice simulation. Very small interstitial loops, a few nanometres in diameter, lying on the (0001) plane of AIN were observed directly for the specimens irradiated to fluences higher than 2·4 × 1024neutrons m-2, and it was determined that those loops have a Burgers vector of (c/2)[0001]. The dilation of thecaxis by neutron irradiation was greater than that of theaaxis, and this anisotropy of the lattice dilation is ascribed to the formation of interstitial loops lying on the basal plane.

ISSN:0950-0839    

DOI:10.1080/09500839008203743

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Résumé

ISSN:0950-0839    

DOI:10.1080/09500839008203744

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The icosahedral structure of A170Pd20Mn10and A165Cu20Fe15quasicrystals in rapidly solidified and annealed states has been examined by electron and X-ray diffraction techniques. Broadening and distortion of the diffraction peaks due to atomic disordering were observed in rapidly solidified A165Cu20Fe15, but were not observed in rapidly solidified A170Pd20Mn10. The rapidly solidified A170Pd20Mn10quasicrystal has a highly ordered atomic arrangement which is nearly the same as that for an Al65Cu20Fe15quasicrystal annealed at a temperature just below the melting point. On the basis of the thermodynamical data, it is presumed that a strong chemical order(bonding) between Pd and Al or Mn prevents the A170Pd20Mn10quasicrystal from generating atomic disordering and phason strains during rapid solidification.

ISSN:0950-0839    

DOI:10.1080/09500839008203745

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

One of the original structural studies on Langmuir-Blodgett (LB) multilayers of 22-tricosenoic acid using the technique of reflection high-energy electron diffraction was performed by Peterson and Russell (1984,Phil. Mag.A,49, 463). In their paper, four distinct structural arrangements of the long-chain fatty acid were identified, where the arrangement adopted by a particular sample was found to depend on the substrate and deposition conditions. The identification of the C2H4subcells in each of these arrangements was made on the basis of a number of assumptions, some of which have subsequently been shown to be erroneous. In particular, the identification of a triclinic subcell appears to be in error and diffraction patterns to which triclinic subcells have been assigned may be re-interpreted as arising from close-packed structures with monoclinic or orthorhombic subcell arrangements.

ISSN:0950-0839    

DOI:10.1080/09500839008203746

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A unified superionic diffusion theory of the photoinduced and the thermally activated dark diffusion of silver in chalcogenide glasses is presented. The theory is based on the proposition that the activation energy for the diffusion of silver in the glasses consists of the following two components: (a) an activation energy for the ionization of deep donor-like interstitial silver impurities, which can be supplied either thermally or through the impurity-induced absorption of photons, and (b) a small, superionic thermal activation energy for the ambipolar diffusion of the ionized impurities. A model for the interfacial reaction through which the initially physically adsorbed silver gains entry into the glasses is also proposed. It is argued that the superionicity which is proposed to underlie photodoping differs in fundamental ways from superionicity encountered in the well known prototype silver superionic conductors, namely, α-Ag2S and α-AgI.

ISSN:0950-0839    

DOI:10.1080/09500839008203747

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

According to the analytic expressions for the spin-lattice coupling coefficients G11and G44in cubic symmetry for d8ions derived from a uniform method based on the relations between the coefficientsG11and the stress dependence of zero-field splitting, the coefficients G11and G44for Ni2+ions on KMgF3and KZnF3crystals have been calculated by using two adjustable parameters (the average covalency) reduction factorNand ligand dipolep) obtained from electron paramagnetic resonance and optical absorption spectra. The absolute values of the calculated results are in agreement with the data obtained from spin-lattice relaxation experiments, and the signs of these coefficients are predicted to be positive from the theoretical calculation.

ISSN:0950-0839    

DOI:10.1080/09500839008203748

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This Letter demonstrates that there is a good correlation between the thermal equilibrium temperatureTEand the optical gapEoptfor undoped hydrogenated amorphous silicon (a-Si: H) and a-Si-based alloys:TE, is proportional toEoptfor both wide-bandgap a-Si-based alloys, such as a-Si1–xCx: H and a-Si1–xNx: H, and narrow-bandgap a-Si1–xCx: H alloys. It is also found that the relaxation process of all thermally-induced metastable changes in these alloys follows a stretched exponential form.

ISSN:0950-0839    

DOI:10.1080/09500839008203749

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor