Peierls stresses (τP) of dislocations of 66 slip systems in 52 crystals were estimated from experimental data either by direct extrapolation of the critical resolved shear stress (τc) vs. temperature ...curve to absolute zero temperature, or from the T0 value at which the temperature dependence of τc vanishes, based on the kink-pair formation enthalpy, which is a function of τP, described by the line tension model of the dislocation. The normalized τP/G (G is the shear modulus) values are distributed over four orders of magnitude, but τP/G values for a group of crystals with the same crystal structure are within an order of magnitude, indicating a homologous nature of τP in crystals. In order to compare the results with the Peierls–Nabarro (P–N) formula generalized to any dislocation character, log(τP/G) values were correlated with crystal parameters. In this generalized P–N plot, most of the plots deviate downwards from the Huntington relation (a revised, original P–N relation) and the results of the discretized P–N models of Ohsawa et al. (Ohsawa K, Koizumi H, Kirchner HOK, Suzuki T. Philos Mag A 1994;69:171), with the deviation becoming larger at large h/δ value, where h is the lattice spacing of the glide plane, and δ is the period of the lattice in the direction of the dislocation glide. In the plot, there is a tendency that the stronger the covalent character, the higher the τP/G value, reflecting the general tendency of the normalized theoretical shear strength of crystals.
Optical and electrical properties of fresh dislocations in GaN bulk crystals deformed plastically at elevated temperatures were reviewed. A dislocation band model was proposed. The fresh dislocations ...of (a/3) 12¯10-type edge dislocations on the (101¯0) prismatic plane induced several photoluminescence peaks at around 1.8, 1.9 and 2.4eV, which implies the formation of radiative recombination centers of the dislocations. Simultaneously, near-band-edge (3.48eV) photoluminescence intensity decreased remarkably for a high-density of non-radiative recombination centers originating in deformation-induced abundant Ga-vacancy related clusters. The intensity variation of yellow luminescence with plastic deformation and subsequent annealing did not relate to the native property of dislocations. Variation of optical absorption dependent on the strain in plastically deformed GaN was understood in a model of the Franz–Keldysh effect by the electric fields associated with charged dislocations (~5.8e/nm). Scanning spreading resistance microscopic images showed many spots with high conductivity around the induced dislocations, showing electrical conduction along dislocations according to the Frenkel–Poole mechanism.
•Optical and electrical properties of fresh dislocations GaN were reviewed.•Their radiative recombination character and band-structure were derived.•Dislocation charges were estimated in the Franz-Keldysh model.•Dislocation conduction by the Frenkel-Poole mechanism was found.
Phonon-phason coupling in decagonal quasicrystals has been discussed in terms of phonon strains induced in crystal approximants. Elastically, decagonal quasicrystals can be classified into two groups ...having different symmetries in the coupling constant tensor; one has only one independent coupling constant, K
4
, and the other has two such constants, K
4
and K
5
. It has been shown that the orthorhombic and monoclinic approximants formed in various alloy systems can be interpreted as resulting from the two different types of decagonal quasicrystals and that a slight distortion in the unit cell of the monoclinic phases is attributable to the effect of one of the coupling constants, K
5
. Phonon strains induced in monoclinic approximants of the Al-Co system have been calculated from their lattice constants and the coupling constants K
4
and K
5
have been evaluated.
We have fabricated photonic quasicrystal lasers with a Penrose lattice that does not possess translational symmetry but has long-range order, and observed coherent lasing action due to the optical ...feedback from quasiperiodicity, exhibiting a variety of 10-fold-symmetric lasing spot patterns. The lattice constant dependence of lasing frequencies and spot patterns show complicated features very different from photonic crystal/random lasers, and we have quantitatively explained them by considering their reciprocal lattice. Unique diversity of their reciprocal lattice opens up new possibilities for the form of lasers.
Precise X-ray diffraction measurements have revealed that phonon (conventional) strain is introduced at the phase transition from an icosahedral quasicrystal to its orthorhombic crystal approximant ...in a Mg-Ga-Al-Zn alloy. From the magnitude of the measured phonon strain, the phonon-phason coupling constant has been evaluated. This constant is approximately −0.03μ (μ: shear modulus) and it is in good agreement with the result of a theoretical calculation reported previously (W.-J. Zhu and C.L. Henley, Europhys. Lett. 46 748 (1999)). This is the first study that experimentally evaluates the phonon-phason coupling constant in any existing quasicrystalline phase.
Dislocations in quasicrystals Edagawa, K
Materials science & engineering. A, Structural materials : properties, microstructure and processing,
07/2001, Letnik:
309
Journal Article
Recenzirano
Quasicrystals have additional elastic degrees of freedom not found in conventional crystals, which are termed phason degrees of freedom. Dislocations in quasicrystals are special in that they are ...inevitably accompanied by the phason strain in addition to the conventional elastic strain. Characteristic features of such quasicrystalline dislocations and plastic properties of quasicrystals are reviewed. Deformation mechanisms in quasicrystals by dislocation motion are discussed.
Experimental evidence is presented which indicates that the total heat capacity in the Al
63
Cu
25
Fe
12
icosahedral phase contains a contribution associated with inconstancy of the charge carrier ...concentration. The contribution has an oscillating temperature dependence and is supposedly traceable to two Schottky-like heat anomalies.
In order to rationalize the homologous nature of the Peierls stress reported in a previous paper (Y. Kamimura et al., Acta Mater. 61 (2013) 294–309), we have calculated numerically the Peierls ...stresses via the Peierls-Nabarro model (P-N model) of the planar core dislocation, using calculated ab-initio γ-surface for a variety of crystals: fcc metals, bcc metals, NaCl type crystals, CsCl type ionic crystals and various tetrahedrally coordinated crystals. The obtained γ-surfaces for the same group of crystals are found to have similar shape and height when normalized by materials parameters, indicating homologous nature. Except for some very soft crystals (τPexp/G ≪ 1 × 10−4), the calculated Peierls stresses for majority of crystals (τPexp/G > 1 × 10−4) are shown, for the first time, to have a correlation with experimental ones reflecting the homologous nature of the γ-surface, although the former are generally larger than the latter by half an order on the average, with an exception of bcc metal in which the strain field of the controlling screw dislocation is known to be non-planar. For very soft crystals, the calculated Peierls stresses are orders of magnitude larger than experimental ones; possible origins of this large discrepancy are discussed.
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