摘要:

The orientation-phase-space-averaged excess volume associated with grain boundaries in nanocrystalline Pd has been deduced from a rule-of-mixtures analysis of density and thermal expansion coefficient measurements. The atomic density is found to fluctuate along the grain-boundary core with an amplitude that could be reduced by low-temperature annealing of the sample. The scaling relation between resistivity and crystallite size changes significantly below approximately 7nm, suggesting that, in this limit, the intrinsic nature of a grain boundary becomes coupled to its spatial extent.

ISSN:0950-0839    

DOI:10.1080/09500839508241616

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

In a study of decagonal quasicrystals and crystalline approximants in the Al-rich binary Al-Co alloy, a new monoclinic crystalline phase has been found in an alloy with a composition of Al11Co4after slow solidification from the melt. The crystal structure of this Al11Co4approximant (with a stoichiometric composition A173.24CO26.75) has been determined by single-crystal X-ray analysis. It has a monoclinic lattice witha= 2.4661(5)nm,b= 0.4056(9) nm,c= 0–7569(2)nm, β = 107.88(3)[ddot], a space group ofP2, 52 atoms in one unit cell and a density of 4.26 Mg m−3. A final R factor of 0.088 has been achieved for 718 reflections. The structure can be viewed as an alternate stacking of flat and puckered layers along its b axis and can be characterized as a two-dimensional period arrangement of pentagonal atomic columns. It has a close structural relationship to both the Al13Co4and the Al13Os4phases. The structures of Al-Co and Al-Cu-Co decagonal quasicrystals with space groups P105/mmc and P10m2 respectively, are discussed on the basis of these crystalline structures.

ISSN:0950-0839    

DOI:10.1080/09500839508241617

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Dislocations in quasicrystals can be observed by conventional diffraction contrast transmission electron microscopy. Within the framework of kinematical theory, the extinction conditions for dislocations are derived in the case of two-dimensional quasicrystals. Analogously to the case of icosahedral quasicrystals, one also expects the existence of a so-called weak-extinction condition, that is the dislocation can be in and out of contrast for collinear vectors. The theory is presented in detail for the case of decagonal quasicrystals and the experimental results are discussed.

ISSN:0950-0839    

DOI:10.1080/09500839508241618

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

Experiments have revealed evidence for grain-boundary sliding and across-column cracking in columnar fresh-water ice loaded under uniaxial compression at −10[ddot]C (Th= 0.96) at strain rates of 10−4and 10−6s−1.

ISSN:0950-0839    

DOI:10.1080/09500839508241619

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

It is found that a new type of defect structure on the {001}-type plane is formed in germanium by deuteron bombardment. High-resolution electron microscopy observation revealed that the defect is of interstitial type with a double period of the {001} plane in the {110} projection. The structure is formally constructed by connecting two {100} 2 × 1 surfaces, rotated by 90[ddot] to each other, in which no dangling bond is involved.

ISSN:0950-0839    

DOI:10.1080/09500839508241620

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The observation of a direct phase transformation from haematite α-Fe2O3(antiferromagnetic) to maghemite γ-Fe2O3(ferrimagnetic) by the mechanical action of grinding is reported. A simple grinding process is used; it is characterized by the presence of a shearing component exerted on the α-Fe2O3particles. All crystallographic and magnetic measurements show existence of a phase transformation a - γ. The interpretation is based on a mechanism using two crystallographic concepts: the orientation relationship between the two phases, and movement of the oxygen planes due to a periodic shearing sequence. The results are also consistent with the phenomena related to the inverse transformation γ → α.

ISSN:0950-0839    

DOI:10.1080/09500839508241621

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

A variety of α-silicon nitride crystals has been examined by transmission electron microscopy. Vacancy clusters have been established to be a common feature of all forms of α-silicon nitride. Clarification of the origin of the vacancies may help to resolve the structural uncertainty of α-silicon nitride.

ISSN:0950-0839    

DOI:10.1080/09500839508241622

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

The kinetics of the reversible light-induced changes of the optical and transport properties at room temperature of sputtered amorphous As2Se3films are presented. It is observed that the evolution of the absorption edge shift (photodarkening effect) of the metastable defect creation process and of the photocurrent decay upon exposure to an intense light take place on completely different time scales. These results show that a hierarchy exists in the appearance of the metastable phenomena. It is concluded that various structural changes probably take place during exposure, with different characteristic times, affecting the optical and the transport properties differently.

ISSN:0950-0839    

DOI:10.1080/09500839508241623

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We propose a new two-electron band theory approach to treat correlated f-electron systems. This involves: first, an exact two-body treatment of the local correlations for a ‘solid-state atom’,i.e.non-spherical local environment of a cerium (or other pertinent) nucleus; then, turning on the interactions giving extended two-electron states (bands). This approach treats the hybridization and exchange Coulomb interaction effects within this two-body treatment on an equal footing. Without invoking the concept of Kondo resonance, it provides a non-magnetic singlet state competing, side by side with other, magnetic states. It explains the wide diversity in f magnetism and the heavy fermion phenomenology, including the specific heat and susceptibility, and most significant, provides an absolute prediction of the Wilson ratio, reproducing the experimental scale and trend in change of the Wilson (low-temperature susceptibility to specific heat) ratio on going from non-magnetic to magnetic heavy fermion materials.

ISSN:0950-0839    

DOI:10.1080/09500839508241624

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor

摘要:

We show that the random-phase model for the electronic wavefunctions gives very reasonable agreement with recent computations of the conductivity for amorphous Si. Furthermore the model also yields the double-sign anomaly in the Hall coefficient observed experimentally, which we have also confirmed by computer simulation. In addition we provide a simple explanation of a computer experiment performed by Weaire and Hobbs in 1993 in which amorphous Si behaves very much like crystalline Si. We argue that this result is not in contradiction with the Hall anomaly.

ISSN:0950-0839    

DOI:10.1080/09500839508241625

出版商:Taylor & Francis Group    

年代:1995

数据来源: Taylor