摘要:

The crystal structure of tetragonal YBa2Cu3O7-δ, with δ close to the critical composition for the tetragonal–orthorhombic transition, has been refined. The oxygen deficiency δ = 0·65(10) is accommodated by both the O(1) and O(2) sites which coordinate the ‘square planar’ Cu(1) site. Structural relaxation around the vacancies is indicated by large anisotropic Debye-Waller ellipsoids in the structural layer formed by these atomic sites. The Y, Ba, Cu(2) and O(3) sites are not involved in the relaxation mechanism. On comparing this structure with the δ ≈ 0 and δ ≈ 1 end-members, we find that with decreasing oxygen content of the structure the Cu(2) valence type transforms from square-pyramidal character towards square-planar character. This effect gives the main contribution to the increase of thec0lattice constant with decreasing oxygen content.

ISSN:0950-0839    

DOI:10.1080/09500838808214750

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Oxygen precipitation in heat-treated Czochralski-grown silicon single crystals has been investigated using γ-ray diffraction combined with small-angle neutron scattering and infrared absorption measurements. Diffuse scattering around the diffraction peaks was observed using γ-rays and this is associated with oxygen precipitation in the silicon lattice. The analysis of the diffuse scattering produces an average precipitate size in agreement with small-angle neutron scattering measurements.

ISSN:0950-0839    

DOI:10.1080/09500838808214751

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

The critical particle diameter for the transition from shearing to looping, ⟨d⟩max, during deformation of alloys strengthened by strong ordered coherent precipitates is related to the antiphase boundary (APB) energy on the {111} planes of the precipitate phase. Theoretical analysis of this process pedicts average APB energies of 0·112±0·030 and 0·161±0·024 Jm−2for the δ′ (Al3Li) and γ′ (Ni3Al) phases respectively. The value for the δ′ phase is about 25% lower than those determined by nearly all other methods, while that for the γ′ phase is about 15% higher. The present method of analysis is more reliable than that of a recent theory proposed by Glazer and Morris. However, because ⟨d⟩maxcannot be measured with the same degree of precision as other quantities, it is argued that more accurate APB energies can be extracted from the analysis of other data on precipitation hardening of alloys containing ordered coherent precipitates.

ISSN:0950-0839    

DOI:10.1080/09500838808214752

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

First-principles calculations of the ground-state linear elastic constants for Ni3Al and Pt3Al are presented. It is found that, while the bulk modulus of Pt3Al (B= 292 GPa) is larger than that of Ni3Al (B= 175 GPa), a far smaller shear-anisotropy factor for Pt3Al is predicted (A= 1·3 andA= 2·9 for Pt3Al and Ni3Al respectively). The anomalous (positive) temperature dependence of flow stress in Ni3Al and its absence in Pt3Al are discussed in terms of the present results.

ISSN:0950-0839    

DOI:10.1080/09500838808214753

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

Ag─Cd alloys have been internally oxidized to produce CdO precipitates within the Ag matrix. Electron microscopy studies revealed that the Ag/CdO interfaces are incoherent which can be explained by the presumably weak bonding forces across the interface and the large lattice misfit. A comparison of lattice images recorded experimentally with those simulated by computer, based on different interfacial structure models, shows that an oxygen plane forms the terminating layer on the oxide side, even at interfacial steps. This result is supported by thermodynamic considerations.

ISSN:0950-0839    

DOI:10.1080/09500838808214754

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor

摘要:

A hydrogen plasma introduced during the interrupting interval when alternating two gases affects the properties of a-Si:H/a-Si1-xNx:H superlattices resulting in the creation of fewer interface defects than the superlattices prepared without the hydrogen plasma.

ISSN:0950-0839    

DOI:10.1080/09500838808214755

出版商:Taylor & Francis Group    

年代:1988

数据来源: Taylor