摘要:

YBa2Cu3O7-δ shows a canvas microstructure, quite similar to a tweed microstructure, which has been interpreted within the framework of the theory of elasticity.

ISSN:0950-0839    

DOI:10.1080/09500839208229271

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The kinetics of the secondary and tertiary oxygen ordering in non-stoichiometric YBa2Cu3O6+δ are studied by the computer simulation method. The effect of long-range interactions between O atoms, the Coulomb repulsion and the strain-induced interaction, on the kinetics is investigated in terms of the crystal lattice site diffusion theory. A previous computer simulation by Semenovskaya and Khachaturyan in 1991 predicted the formation of (110) twins of the primary O(I) ordered phase. It is shown in the present work that the nanoscale O(I) twins strongly effect the path of the secondary and tertiary ordering reactions. Secondary ordering within the twins results in the formation of the metastable 2a0× 2a0phase prior to the occurrence of the stable 2a0×a0(or O(II)) ordered phase. Twin boundaries also promote the appearance of the tertiary ordered O’ phase with 2√2a0× 2√2a0× 3a0unit cell.

ISSN:0950-0839    

DOI:10.1080/09500839208229272

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A closed-form expression for the recombination function in steady-state illuminated hydrogenated amorphous silicon (a-Si: H) is given for the case that recombination occurs mainly via the dangling-bond states. Based on the three charge conditions (positive, neutral or negative) for the dangling bonds, the three corresponding occupation functions are derived; an expression for the recombination functionRDBis thereby obtained. The latter differs considerably from the commonly used Shockley-Read and Hall function RSRH. As an illustration, the limiting carrier in an a-Si: H p-i-n solar cell under reverse voltage is shown to be either one with a longer drift length, using KSRH, or one with a shorter drift length, usingRDB. Therefore one can conclude that the use of the proper recombination function is critical for a discussion of the relevant physical parameters involved in the description of p-i-n devices. Interpretation for ambipolar diffusion length and photoconductivity are also mentioned as cases where the use of the appropriate occupation and recombination functions are of decisive importance.

ISSN:0950-0839    

DOI:10.1080/09500839208229273

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Current transients due to evolution of metastable corrosion pits on stainless steel in chloride solution are shown to be preceded by sharp current spikes. These current spikes are measured in the picoampere regime and represent microscopically violent nucleation events. Not all nucleation events survive to produce metastable pits: many die through repassivation immediately after nucleation.

ISSN:0950-0839    

DOI:10.1080/09500839208229274

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Small-angle tilt boundaries and small-angle twist boundaries are familiar features of crystalline microstructures but small-angle shear boundaries are much less well known. Shear boundaries may be composed of cross-grids of either edge or screw dislocations. This paper reports some observations of shear boundaries on {111} planes in tetragonal TiAl which consist only of screw dislocations. In the electron microscope, shear boundaries look very similar to twist boundaries but they differ in that their two sets of dislocations have the same sign whereas twist boundaries have two sets with opposite signs. Asymmetric shear boundaries, composed of two sets of dislocations with different spacings, can be described as a superposition of a symmetric shear boundary and a twist boundary. An extreme case is a simple shear boundary which has just one set of screw dislocations.

ISSN:0950-0839    

DOI:10.1080/09500839208229275

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In the L12long-range-ordered structure, superlattice dislocation form complicated configurations and barriers. Kear–Wilsdorf (KW) barriers are screw superlattice dislocations which are totally dissociated on cube planes. The driving force for their formation is the elastic repulsion of the superlattice partials constituting the screw superlattice dislocation, balanced by a lower antiphase boundary energy on cube {001} planes compared with that on octahedral {111} planes. The striking result of this letter is the observation of screw superlattice dislocations partly dissociated on cube and octahedral planes. We call them incomplete KW barriers. Their Occurrence provides evidence that the KW barriers are products formed during deformation and not a consequence of unloading after deformation or artefacts due to specimen preparation.

ISSN:0950-0839    

DOI:10.1080/09500839208229276

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The theoretical modelling of the temperature-dependent metastable dangling-bond density in undoped hydrogenated amorphous silicon (a-Si: H) is critically reviewed. It is shown that thermal broadening of the band tails provides the main contribution to the observed increase in the deep-defect density in a-Si: H with increasing temperature. The possible structural origins of this phenomenon are briefly discussed.

ISSN:0950-0839    

DOI:10.1080/09500839208229277

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A part of the Al–Cu–Co alloy system, including the region of the decagonal phase, was studied by scanning electron microscopy, energy-dispersive X-ray analysis and X-ray diffractometry. The decagonal phase in the Al–Cu–Co system was found to behave as a stable phase in the temperature range 550–1000°C. Its compositional region depended strongly on temperature. In a wide range of alloy compositions the decagonal phase produced at higher temperatures became supersaturated at lower temperatures. The formation of (Al, Cu)13Co4in an aged supersaturated single-decagonal-phase sample was observed.

ISSN:0950-0839    

DOI:10.1080/09500839208229278

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In a recent letter by Zoli in 1991 it was claimed that the difference between the quasiharmonic values for the atomic mean square displacement and the anharmonic values is, in f.c.c. metals, up to 91%. This result arises from inaccurate calculations of the harmonic and quasiharmonic values. Properly calculated, the quasiharmonic values deviate by only about 10% from the anharmonic values.

ISSN:0950-0839    

DOI:10.1080/09500839208229279

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor