摘要:

The calculated defect chemistry of La2CuO4, Nd2CuO4, and Pr2CuO4shows why the former material exhibits (super) conductivity apparently only via holes and the latter two materials only via defect electrons

ISSN:0950-0839    

DOI:10.1080/09500838908206455

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

On the basis of a simple geometrical analysis, exact formulae for the average misorientation angle of random tilt boundaries in the structural unit and disclination models are obtained. Two important consequences following from these formulae are considered: the relation between the Burgers vector of grain boundary dislocations and the geometrical parameters of short-period areas composing the random boundary, and an exact expression for the Burgers vector of a dislocation equivalent to a disclination dipole with given strength and structure of the related boundary

ISSN:0950-0839    

DOI:10.1080/09500838908206456

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A rapidly solidified Al65Cu20Fe15icosahedral alloy has been studied by extended X-ray absorption he structure above the Cu and Fe K absorption edges. The local order has been determined around Cu and Fe atoms and compared with results obtained previously in other icosahedral alloys

ISSN:0950-0839    

DOI:10.1080/09500838908206457

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Al65Ru15Cu20icosahedral quasicrystals, which were prepared by conventional melting and melt-quenching methods, have been examined by electron and X-ray diffraction. Superlattice reflections interpreted by face-centred six-dimensional hypercubic lattices, which are observed in the conventionally solidified quasicrystal, are considerably weaker or non-existent in the rapidly solidified material. The weak superlattice reflections become stronger upon annealing at 750°C for 30min. The result shows that atomic ordering is suppressed by rapid cooling and the disordered quasicrystal produced transforms to the ordered one at about 750°C

ISSN:0950-0839    

DOI:10.1080/09500838908206458

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

We have established a simple icosahedral to face-centred icosahedral ordering transformation in Al–Mn quasicrystals. This result strongly supports the view that the recently discovered face-centred icosahedral quasicrystal in ternary Al–Cu–Fe and related alloys represents a long-range superstructure of simple icosahedral quasicrystals

ISSN:0950-0839    

DOI:10.1080/09500838908206459

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

For superconducting Nb3Sn the critical current, or pinning force, density as a function of grain size and applied magnetic field data are shown to be in general agreement with computations based on flux-line-lattice shear, activated by Frank-Read source dislocations. The formalism predicts an optimum effective grain size and maximum critical current density which can be sustained at a given applied magnetic field. Neutron irradiation effects are also consistent with predicted results

ISSN:0950-0839    

DOI:10.1080/09500838908206460

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

Diffusion of Mn-54 in pure aluminium between 917 and 843 K has been measured by the serial-sectioning technique. The penetration plots were fitted by the same general solution of the diffusion equation used by us earlier for iron diffusion in aluminium. In this solution the surface flux controlled by a surface barrier (characterizing the dissolution of tracer atoms from the intermetallic phases formed in the near surface layer) is also included. Our results can be expressed asD= (8·+6·8−3·3) × 10−4exp[(−1·96 ± 0·04)eV/kT] m2s−1, and are in reasonable agreement with the most recent results of Fujikawa and Hirano. However, our activation energy, as expected from the surface barrier effects is lower by 0·29 eV

ISSN:0950-0839    

DOI:10.1080/09500838908206461

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

A novel method for determining the concentration and distribution across sites of substitutional impurities in crystals is described, as an alternative to the usual ratio method of atom location by the channelling enhanced microanalysis (ALCHEMI) technique. The integrated X-ray counts for emission from impurity and host atom species under strong zone-axis diffraction conditions are analysed using standard multivariate statistical procedures. This enables both the total concentration and the fractional site occupancy of the impurity species to be determined, together with quantitative estimates of the uncertainties in these quantities. This method of analysis is illustrated through the determination of the site occupancy of Fe in a Cr2MnO4spinel. Advantages of this technique include reduced sensitivity both to the effects of delocalization and to the effects of experimental errors compared with standard ALCHEMI analyses.

ISSN:0950-0839    

DOI:10.1080/09500838908206462

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor

摘要:

The effects of 1 MeV electron irradiation on crystalline Ge/Al or Si/Al bilayer specimens at 10 K have been studiedin situby high-voltage electron microscopy. It is demonstrated that a crystalline-to-amorphous (c-to-a) transition takes place at the interface of a Ge/Al bilayer specimen only if the Ge layer faces the incident beam, while amorphization occurs in a Si/Al bilayer specimen regardless of the incident beam's direction with respect to the bilayer specimen. Diffuse rings in selected-area diffraction patterns first appear at a fluence of about 3 × 1023cm−2(about 30, 19 or 18 displacements per atom in Ge, Si or Al respectively), and the amorphous volume fraction increases with increasing fluence. These results can be understood in terms of a simple recoil-implantation mechanism.

ISSN:0950-0839    

DOI:10.1080/09500838908206463

出版商:Taylor & Francis Group    

年代:1989

数据来源: Taylor