摘要:

The temperature dependence of the high-temperature superconductor surface resistance is calculated on the basis of the bipolaron Bose condensation model. The correlation between the theoretical results and experimental data is discussed. Several constituents of the residual resistance are described.

ISSN:0950-0839    

DOI:10.1080/09500839208207539

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

We present the first computer simulations of the Hall effect for a realistic model of a solid, namely amorphous silicon, and succeed in verifying the anomalous change in sign of the Hall coefficient as the Fermi energy is moved from the valence band to the conduction band in accordance with the observations of LeComber, Jones and Spear in 1977. A model for this behaviour is proposed based on previous computations of the spectral function and a theory of gap formation.

ISSN:0950-0839    

DOI:10.1080/09500839208207540

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The deformation behaviour of two-phase (γ + α2) titanium aluminide was investigated by high-resolution transmission electron microscopy. Specimens were deformed in compression at room temperature well beyond the yield point. The α2-Ti3Al lamellae within the γ-TiAl matrix were observed to deform by shearing when intersected by twins. In addition to dislocation slip, plastic deformation in γ-TiAl was found to proceed by (a/6)<112] twinning partial dislocations, as revealed by the steps on twin interfaces, and by the creation of a three-plane (9R) deformation-induced structure parallel to pre-existing twin interfaces. Formation of the 9R structure is due to an antitwinning operation on every third plane. The core structure of (a/6)<112] twinning partial dislocation steps appears narrow compared with similar (a/6)<112] partial dislocations associated with growth ledges at the γ-α2interface. These observations and deformation mechanisms are discussed in terms of the structure of γ-α2and twin interfaces.

ISSN:0950-0839    

DOI:10.1080/09500839208207541

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Cd(S, Se) nanocrystals were developed in silicate glass by heat treatments and were characterized by high-resolution transmission electron microscopy. They are crystallized in the hexagonal structure of wurtzite type. Their average size increases with increasing heat-treatment time from 5 to 13 nm at 700°C and from 5 to 10 nm at 675°C. The crystal morphology depends on the size. Below a critical size sc, the shape is close to either a sphere or a hexagonal prism with nearly equivalent dimensions in every direction. Above sc, the crystallites definitely adopt a prismatic habit, growing longer in the direction of the c axis. The critical size depends on the temperature of the heat treatment: At 700°C,scis about 10nm and, at 675°C, it is around 6–7 nm. The basal faces of the prism present an asymmetry, indicating different growth rates in opposite directions of the c axis, in relation to the polarity of the wurtzite structure.

ISSN:0950-0839    

DOI:10.1080/09500839208207542

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

High-pressure resistivity measurements have been performed on Ge7·5AsxTe92·5-x. (x = 20, 40, 45, 50 and 55) and Ge10AsxTe90-x(x= 15, 20, 35, 40, 45 and 50) glasses. The glasses show reversible metallization behaviour under pressure. The pressure derivative of the logarithm of the resistivity of the glasses is a minimum at glass compositions corresponding to the average coordination number ⟨r⟩ = 2·60. This behaviour is interpreted on the basis of the existence of a critical composition in glasses with a layered structure.

ISSN:0950-0839    

DOI:10.1080/09500839208207543

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

A critical test has been presented to establish the nature of the kinetic pathways for the decomposition of Fe–12 at.% Si alloy below the metastable tricritical point. The results, based on the measurements of saturation magnetization, establish that a congruent ordering from B2→ D03precedes the development of a B2 + D03two-phase field, consistent with the predictions in 1976 of Allen and Cahn.

ISSN:0950-0839    

DOI:10.1080/09500839208207544

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

Local dynamics of the lattice is taken into consideration to modify the original Einstein model of lattice dynamics, and the modified Einstein model is tested by evaluating the thermodynamic properties of crystalline KBr. Specifically, the thermal expansion, thermal expansion coefficient and specific heat at constant volume have been evaluated as functions of temperature at atmospheric pressure for crystalline KBr using a realistic potential of the formA1R−9+A2R−6±A3R−1, and normal-mode frequencies obtained from local dynamics of two particles allowed to oscillate in a static potential field due to all the rest of particles, assumed at rest in their mean positions. The temperature dependence of these thermodynamic functions is examined in comparison with the available experimental data, and reasonable agreement is observed.

ISSN:0950-0839    

DOI:10.1080/09500839208207545

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

In a longitudinal magnetic field, oscillations of ellipticity have been found for the propagation of shear ultrasound along the tetragonal axis in superpure indium. A suggested interpretation is based on a theory of magnetoacoustic geometric oscillations taking into account the frequency dispersion.

ISSN:0950-0839    

DOI:10.1080/09500839208207546

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

The precipitates which develop during annealing in a Co–Ni–Cr–Nb superalloy are faulted. The nature of these faults has been investigated using high-resolution electron microscopy. The precipitates have an hexagonal ordered structure and several types of stacking fault can theoretically be present. Only one type of fault is observed which corresponds to the less energetical fault.

ISSN:0950-0839    

DOI:10.1080/09500839208207547

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor

摘要:

This Letter presents the first clear demonstration of a grain-boundary dislocation generation mechanism in ice. The dislocations generated as semihexa-gonal loops were observed to glide on the basal plane.

ISSN:0950-0839    

DOI:10.1080/09500839208207548

出版商:Taylor & Francis Group    

年代:1992

数据来源: Taylor