摘要:

The infrared properties of icosahedral phases of AI-Mn and AI64Cu22Fe14are studied. In principle, the observed overall spectral shapes of the optical conductivities of both samples correspond to the low density of states at Fermi level and/or to the localization tendency of states. The observed anomalies (shoulders and bumps) in the conductivities are discussed in terms of interband transitions and phonons. We observed good qualitative agreement between our results and the predictions of the theory of compartmentalization which was suggested to describe the electronic properties of quasicrystals and rational approximants.

ISSN:0950-0839    

DOI:10.1080/09500839308241267

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

{103}⟨331⟩ slip is found to be activated in MoSi2single crystals by deformation along [001] in uniaxial compression at 1000°C. The {103} slip plane has been determined by slip trace analysis. Observations by transmission electron microscopy reveal the presence of screw dislocations with a Burgers vector of ½⟨331⟩. However, ½⟨331⟩ dislocations of mixed character lying along the ⟨ 010 ⟩ direction are observed to have decomposed into two other perfect dislocations by the energetically favourable reaction

ISSN:0950-0839    

DOI:10.1080/09500839308241268

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

Misfit dislocations in Cd1−xMnxTe/CdTe(001) epitaxial structures with low mismatch (0·3%) are compared for cases where the deposit is in tension and in compression. Where the deposit was in tension, misfit dislocations were parallel to interfacial ⟨ 110 ⟩ directions and were either 60° dislocations with ½⟨ 110 ⟩ Burgers vectors inclined to the interface or were 90° dislocations with ⅙⟨ 112 ⟩ Burgers vectors bounding intrinsic stacking faults. When the deposit was in compression, misfit dislocations had ½⟨ 110 ⟩ Burgers vectors inclined to the interface but lay predominantly in ⟨ 100 ⟩ directions. These observations are explained by a model where the forces acting on the individual Shockley partials of a dissociated ½⟨ 110 ⟩ dislocation tend to widen and narrow the stacking fault for the tension and compression cases respectively. It is argued that the tendency of the dislocation to become undissociated when the deposit is in compression allows alternative slip planes to operate and that ⟨ 100 ⟩ segments of dislocation are generated by a multiple cross-slip mechanism rather than {110} glide, as previously suggested by Bonar, Hull, Walker and Malik. Evidence for the operation of the multiple cross-slip mechanism in a ZnTe/Cd1−xMnxTe structure with a high mismatch (5·6%) is also presented and the results compared with those for the lower-mismatch structures.

ISSN:0950-0839    

DOI:10.1080/09500839308241269

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The identity of dislocations which contribute to plastic deformation of polycrystalline MoSi2when compressed at 1400°C has been determined using transmission electron microscopy. It has been confirmed that dislocations with Burgers vectors lying parallel to ⟨ 100 ⟩ and ⟨ 111 ⟩ are activated in response to the applied stress. In addition, the deformation microstructure is characterized by the presence of networks containing dislocations with Burgers vectors parallel to ⟨ 100], ⟨ 110] and ⟨ 111 ⟩. It has been shown that dislocations with Burgers vectors lying parallel to ⟨ 111 ⟩ are dissociated. A simple explanation has been developed to account for the occurrence of dissociation of particular dislocations, and on the basis of this model the dissociation is represented by

ISSN:0950-0839    

DOI:10.1080/09500839308241270

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

An analytical treatment of quasi-equilibrium carrier transport in disordered materials at moderate electric fields is presented. The transport equation derived has the form of a conventional Fokker-Plank equation with drift, diffusion and field-assisted diffusion terms. General formulae are obtained for drift mobility as well as for the coefficients of conventional and field-assisted diffusion. The temperature dependences of these quantities are considered for different energy distributions of localized states.

ISSN:0950-0839    

DOI:10.1080/09500839308241271

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

摘要:

The formation range and thermal stability of the icosahedral phase produced by melt spinning were investigated in ternary Al‒Cu‒Ru alloys by X-ray diffraction and transmission electron microscopy. The stable face-centred icosahedral (FCI) phase is formed in a wide region where the condition for the valence electron-to-atom ratioe/a≈1·75is satisfied. Shifts of diffraction peaks to larger angles were observed during an annealing study of the melt-spun Al64Cu23Ru13sample. The decrease in the quasilattice constant is considered to result from atomic ordering in the FCI phase. A new type of stable approximant (1/0 cubic type) was found to exist near the composition Al71Cu7Ru22. This structure has been determined to be simple cubic with a lattice constanta= 7·7 Å. The H3U structure is proposed for this approximant.

ISSN:0950-0839    

DOI:10.1080/09500839308241272

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor

ISSN:0950-0839    

DOI:10.1080/09500839308241273

出版商:Taylor & Francis Group    

年代:1993

数据来源: Taylor