摘要:

Differential scanning calorimetry performed on specimens of polycrystalline NiSb, quenched from 750 and 800°C, has revealed only one annealing stage at about 280°C. The activation energy (Ea=1·15 eV) and the order of reaction for this stage (m= 1) have been determined by a kinetic analysis. These results are discussed and it is suggested that the stage is due to the annealing of Ni quenched-in monovacancies.

ISSN:0950-0839    

DOI:10.1080/09500839208207517

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Positron lifetime measurements in He-implanted Ni and Ni-Ti alloys containing dilute concentrations of Ti, during isochronal annealing, are reported. In the initial annealing stage of Ni-Ti alloys, only a single lifetime ranging from 160 to 180ps is observed, in contrast with the two lifetimes seen in pure Ni. This indicates saturation positron trapping at helium-bound Ti-vacancy complexes, formed in high concentrations. Lattice statics calculations of the He binding energy at various defect complexes in Ni-containing Ti give credence to the above interpretation. Above 800 K, two lifetimes are resolved in Ni-Ti alloys, where the longer lifetime τ2increases with a sharp reduction in its intensity. This is indicative of He bubble growth. The bubble radiusrBand bubble concentrationCBare obtained from an analysis of positron lifetime parameters. These results indicate that, for a given annealing temperature,rBis smaller by a factor of two andCBhigher by nearly an order of magnitude in Ni-Ti than the corresponding values in pure Ni. This is explained as due to significant retardation of bubble growth on the addition of Ti to Ni, where the Ti impurities cause an impediment to bubble migration and coalescence.

ISSN:0950-0839    

DOI:10.1080/09500839208207518

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Several repeat units and repeat schemes for the Al-Cu-Co decagonal phase and its crystalline approximants are proposed. An inherent strain is introduced into the structure through repetition of these units. The transition from the crystalline to the quasicrystalline state appears to be due to an increase in twinning, which reduces this strain.

ISSN:0950-0839    

DOI:10.1080/09500839208207519

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The temperature dependence of Si(111) surface structures has been studied. Reflection electron diffraction intensities have been measured for Si(111) clean surfaces as a function of temperature. Diffraction intensities change at 830,1110 and 1410 K, corresponding to a low-temperature 7 × 7 phase↔a high-temperature 7 × 7, 7 × 7 ↔ 1 × 1 phase transition, and a surface order-disorder transition respectively. These temperatures are equivalent to 0·49(≈ 3/6)Tm, 0·66(≈ 4/6)Tm, and 0·84(≈ 5/6)Tmrespectively, whereTmis the melting temperature of bulk Si on the absolute temperature scale. The significance of these temperatures is discussed in relation to the crystal surface sites, for example kinks, ledges and terraces.

ISSN:0950-0839    

DOI:10.1080/09500839208207520

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This work presents a direct simulation of the processes of electron-phonon interaction which follow the formation of an excited electron gas such as that produced by high-energy implants. The simulation method is of the molecular dynamics type and is based on a quantum-mechanical representation. The calculations indicate the conditions under which lattice disorder or melting take place.

ISSN:0950-0839    

DOI:10.1080/09500839208207521

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

While extrinsic photoeffects in chemically vapour-deposited thin films of diamond can originate from impurity-controlled photogeneration and photoinjection of carriers from contiguous metal electrodes, it is important, and yet difficult, to differentiate between these two distinctive processes. Detailed studies and results are described, involving the use of non-absorbing water-based electrodes which allow a clear distinction between these two mechanisms to be made. In addition, the near-infrared-visible photoeffect in diamond thin films, as in single-crystal diamond, is associated with the photoionization of unionized acceptors based on its observed quenching in nitrogen-doped compensated films.

ISSN:0950-0839    

DOI:10.1080/09500839208207522

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The Bitter pattern technique has been used in order to decorate the magnetic structures, exhibited by a single crystal of the high-Tcsuperconductor YBa2(Cu, Au)3O7-δat 4·2 K as a function of the applied magnetic field in a ‘field-cooling’ condition. The decoration reproducibility of some structural faults, under different magnetic fields, has been examined. The two-dimensional lattice of magnetic flux lines, rectangular at low fields, has been found to evolve towards a hexagonal symmetry at elevated magnetic fields; the variation in the average Wigner—Seitz cell area, relative to a magnetic flux line quantum, appears to be inversely proportional to the applied magnetic fields.

ISSN:0950-0839    

DOI:10.1080/09500839208207523

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor