摘要:

The local translational order of the icosahedral quasicrystalline phase in rapidly solidified V41Ni36Si23has been investigated by means of selected-area electron diffraction and high-resolution electron microscopy. Experimental results show that translational order always occurs in the twofold direction and can be observed when the quasicrystal is examined along its fivefold and threefold as well as twofold axes. Sometimes it occurs in two or three coplanar twofold directions simultaneously. In these cases some crystalline islands exist in the icosahedral quasicrystal and this corresponds to the initial stage of transformation from a quasicrystal to the stable crystalline phase.

ISSN:0950-0839    

DOI:10.1080/09500838708225370

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The ability of amorphous metallic alloys to resist irradiation-induced structural changes will depend on the composition of the alloy and the particle fluences used. In this paper we show that a fast neutron fluence of 1020cm−2can induce local crystallization in a refractory NiTi glass. For specimens irradiated with lower fluences, the mode of crystallization of the amorphous matrix is changed from that of a primary process to a eutectic mechanism.

ISSN:0950-0839    

DOI:10.1080/09500838708225371

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

When thin-foil specimens of InSb are heated in the vacuum of an electron microscope, a depletion of Sb takes place because of the preferential evaporation of Sb. This results in the formation of a novel non-stoichiometric (In-rich) solid phase having a cubic structure with a lattice parameter of 5·9 Å, which is about 10% smaller than that of InSb. It has been shown that the twin-orientation relationship exists between the matrix and the non-stoichiometric phase.

ISSN:0950-0839    

DOI:10.1080/09500838708225372

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The computer simulation of lattice-gas models of solids by Monte Carlo methods is significant for the theory of atomic migration and transport in alloys, solid solutions of hydrogen in metals, fast-ion conductors, etc. This paper presents certain exact limiting relations which provide useful checks on such simulations on complex models. These relations specify the way macroscopic transport coefficients and associated quantities (‘correlation factors’) depend upon isotopic ratios and vacancy fraction.

ISSN:0950-0839    

DOI:10.1080/09500838708225373

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Internal friction measurements with a superimposed bias stress have provided evidence for geometrical kink migration on screw dislocations in iron. This intrinsic process causes a relaxation phenomenon in internal friction which has been identified with the occurrence of a subpeak (below 20 K) of the α-peak. The effect of different bias stress has allowed us to evaluate the kink migration energy,Emk≲ 0·001eV.

ISSN:0950-0839    

DOI:10.1080/09500838708225374

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The influence of impurity elements on the strength of neighbouring metal–metal bonds is investigated using a simple tight-binding model. We show that the quantum-mechanical response function of the metal host plays a central role in determining whether the bond is weakened or strengthened. The Messmer–Briant model, which is based on classical concepts of charge flow due to differences in electronegativity, is not applicable to metals because of their perfect screening. Recent experiments on impurity core level and isomer shifts should not be taken as a direct measure of neighbouring metal–metal bond decohesion.

ISSN:0950-0839    

DOI:10.1080/09500838708225375

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

An analytical WKB approximation of the numerical results of Rösneret al.(1984) for the hydrogen ground-state wavefunctions at megatesla fields is used to solve the percolation problem for transport involving donors in direct-gap semiconductors. We show that the transport coefficients thus obtained account for the magnetoresistance data in GaAs, to an accuracy comparable with previous theoretical work.

ISSN:0950-0839    

DOI:10.1080/09500838708225376

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

A high-resolution X-ray scattering experiment has been performed on quasicrystalline (T2) and crystalline (R) phases of AlCuLi alloys. Peak widths determined from the diffraction profile of the R phase are found to scale with momentum transferG, similar to the strain-broadening effect seen in conventional crystals with small unit cells. A narrowing of peak widths on annealing is also observed. On the other hand, diffraction peak widths in I-phase samples obtained by rapid solidification are found to scale with phason momentumG1, similar to that observed in large faceted crystals. Thermal annealing of the I phase is found to have no effect on peak widths. Our findings are discussed in the light of models for crystals and quasicrystals.

ISSN:0950-0839    

DOI:10.1080/09500838708225377

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

Based on experimental results of transient photoresponse and photo-induced reversible echanges for the same a-Si : H pin structure, a model is proposed for the Staebler–Wronski effect, by which reversible changes of the photo-induced dangling-bond density can be interpreted. We show that the origin of the effect is a space-charge redistribution caused by the corresponding reversible changes of internal electric fields in a-Si : H. A discussion is given of the reversible transitions described by T+3+ T−3⇌2T03during illumination and annealing, respectively.

ISSN:0950-0839    

DOI:10.1080/09500838708225378

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor

摘要:

The effect of Fe impurity on the superconductivity of Y1Ba2Cu3O9−xhas been investigated by X-ray diffraction, electrical resistance and magnetic susceptibility measurements. The results show thatTcand the diamagnetic susceptibility decrease with increasing Fe content. The specimens with O·35wt.% Fe show no superconductivity at liquid nitrogen temperatures, which corresponds to a change in the intensities of three dominent X-ray diffraction peaks. The crystal structure of the Y1Ba2Cu3O9−xphase changes from being orthorhombic to a tetragonal perovskite with increasing Fe content.

ISSN:0950-0839    

DOI:10.1080/09500838708225379

出版商:Taylor & Francis Group    

年代:1987

数据来源: Taylor