摘要:

X-ray section topography using synchrotron radiation has been applied to the examination of large (up to about 2 cm thickness) uncut crystals of two important organic nonlinear optical materials, (−)2-(α-methylbenzylamino)-5-nitropyridine (MBA-NP) and urea. The resulting topographs contain well defined images of dislocations, growth sector boundaries, growth striations and inclusions. Initial observations relating to the growth behaviour of the crystals are discussed in terms of the nature and distribution of the growth defects revealed.

ISSN:0950-0839    

DOI:10.1080/09500839008203732

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The effects of magnetic annealing on recrystallization and grain-boundary character distribution (GBCD), the type and frequency of grain boundaries, have been studied in iron-9 mol% cobalt alloy polycrystals in the range of magnetic field strength up to 04 MA m−1(5kOe). It was found that magnetic annealing retards recrystallization and affects the GBCD, particularly the frequency of low-angle boundaries in recrystallized polycrystals of the alloy. The frequency of low-angle boundaries increases with increasing strength of the magnetic field, exceeding the value predicted for a random polycrystal.

ISSN:0950-0839    

DOI:10.1080/09500839008203733

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

It has been shown that the disclination dipole description of a grain boundary is equivalent to the surface dislocation model in the limit of low angular misorientations. Neither model is compatible with the classical formulation of Burgers, which is shown to be incomplete. For larger angles, on the other hand, the situation becomes more complex, and the surface dislocation approach is seen to be the most desirable.

ISSN:0950-0839    

DOI:10.1080/09500839008203734

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This Letter presents a new model to account for the mechanism of enrichment of Sb on cavity surfaces grown in heat-treated zones of low-alloyed ferritic steels. The model, based on the energetic balance between the change of the atomic free energy of an impurity atom that leaves a cavity inner surface and the elastic energy needed to accommodate the impurity atom in the crystal lattice, accounts well for the experimental Sb enrichment factors. The enrichment factors were measured as a function of the cavity radii by means a high-resolution Auger microprobe. The grain-boundary cavity surfaces were obtained, by fracturing in ultra-high vacuum a 1/2Cr1/2Mo1/4V steel sample, heat-treated at 800K for 9 × 104h.

ISSN:0950-0839    

DOI:10.1080/09500839008203735

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

This paper contrasts recent discussions of the theory of strengthening by coherent precipitates. The most important difference is in the assumed condition at maximum hardness. In one treatment, the maximum hardness is reached when dislocations first begin to loop precipitates, and is hence controlled by the largest particles in the precipitate size distribution. In the other treatment, the maximum hardness occurs when precipitates of average size are looped, and is hence controlled by the average precipitate size. More general theories of hardening by distributions of particles of different strength support the former treatment, but are incomplete. The experimental data is ambiguous. Experiments are needed to resolve the issue.

ISSN:0950-0839    

DOI:10.1080/09500839008203736

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Starting with a model of real-space bosons as proposed by the present author, by Micnaset al.and others, with bosons the main current carriers aboveTc, an explanation is proposed for the very small entropy at the transition observed by Loramet al., much less thankBIn 2 per carrier. This involves the assumption, made previously, that the bosons move in an impurity band, and takes into account their mutual repulsion and the existence of Anderson localized states in the band.

ISSN:0950-0839    

DOI:10.1080/09500839008203737

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A defect structure produced by fast-neutron irradiation of YBa2Cu3O7–xhas been investigated using transmission electron microscopy. Correlations with changes in bulk properties are suggested.

ISSN:0950-0839    

DOI:10.1080/09500839008203738

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

A new approach high-resolution electron microscopy combined with computer-imaging techniques is used to delineate the distorted atomic configurations that underlie the tweed structure in Y-Ba-Cu-O oxides. It appears that the quasi-periodic shear displacements along [110] anddirections are directly responsible for both the tweed contrast observed under the two-beam condition and the streaking in diffraction. The modulation is associated with the presence of off-stoichiometric oxygen occurring either when the trivalent elements substitute for Cu in the chain site or when oxygen is removed from YBa2Cu3O7.

ISSN:0950-0839    

DOI:10.1080/09500839008203739

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

Hole transport has been investigated in films of solid solutions of N,N′-diphenyl-N,N′-bis(3-methylphenyl)-[1,1′-biphenyl]-4,4′-diamine (TPD) in bisphenol A polycarbonate and polystyrene. Rather than being ‘inert’ as previously assumed, the binder plays a major role in influencing the rate of charge exchange between molecules. It is found that the absolute values of the drift mobilities, their electric-field dependence and the activation energies are strong functions of the binder polymer employed to cast the films. At equivalent low molecular concentrations, the hole mobility in films of molecular dispersions in polystyrene is two orders of magnitude higher than that observed in dispersions in polycarbonate, on which most investigations reported in the literature have been carried out. The increased mobility of dispersions in polystyrene is directly related to the reduction in the activation energies.

ISSN:0950-0839    

DOI:10.1080/09500839008203740

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor

摘要:

The anisotropy of the threshold energy for atom displacement,Ed, in Au and Ag at 473 K has been determined. Whereas in Ag, minima ofEdare found close to the ⟨100⟩, ⟨110⟩ and ⟨210⟩ directions (Ed= 13–18eV), atom displacement in Au requires least energy near ⟨100⟩ (15–19eV). So far Au is the only f.c.c. metal exhibiting a distinctly lowerEdin the ⟨100⟩ than in the ⟨110⟩ direction. This is discussed in terms of the atomic processes controlling the propagation of replacement collision sequences.

ISSN:0950-0839    

DOI:10.1080/09500839008203741

出版商:Taylor & Francis Group    

年代:1990

数据来源: Taylor