494 research outputs found
Mechanism for liquid phase epitaxial growth of nonequilibrium compositions producing a coherent interface
Journal ArticleA model is presented for growth by so-called composition pulling, wherein an epitaxial deposit grows coherently but with a composition different from that which would be in bulk equilibrium with the liquid phase from which growth occurs. The breakdown of coherent growth occurs when a dislocation nucleates at a ledge at the growing solid-liquid interface. An expression for the critical condition for breakdown is presented
Anisotropic elastic fields of twist boundaries
Relations for linear anisotropic elastic fields of parallel arrays of dislocations are developed. These fields are used to compute the displacement fields of twist boundaries composed of a square grid of screw dislocations. For gold, the results are shown to agree to first order with fields deduced from X-ray diffraction studies and from atomistic simulations for twist boundaries in gold.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/30031/1/0000399.pd
Image forces on screw dislocations in multilayer structures
Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26533/1/0000072.pd
Hydrogen adsorption at dislocations and cracks in Fe
Solute adsorption to dislocations and cracks is considered in both the Boltzmann and Fermi-Dirac models. Explicit sums are developed for the integral amount of solute adsorbed in the defect fields. Examples of the use of the method are presented for the case of hydrogen in iron and compared with earlier results. The similarity of the condensed atmosphere of hydrogen to hydride precipitation is noted and its relevancy to hydrogen embrittlement models is discussed.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/22483/1/0000024.pd
Melting as a String-Mediated Phase Transition
We present a theory of the melting of elemental solids as a
dislocation-mediated phase transition. We model dislocations near melt as
non-interacting closed strings on a lattice. In this framework we derive simple
expressions for the melting temperature and latent heat of fusion that depend
on the dislocation density at melt. We use experimental data for more than half
the elements in the Periodic Table to determine the dislocation density from
both relations. Melting temperatures yield a dislocation density of (0.61\pm
0.20) b^{-2}, in good agreement with the density obtained from latent heats,
(0.66\pm 0.11) b^{-2}, where b is the length of the smallest
perfect-dislocation Burgers vector. Melting corresponds to the situation where,
on average, half of the atoms are within a dislocation core.Comment: 18 pages, LaTeX, 3 eps figures, to appear in Phys. Rev.
Dislocations and the critical endpoint of the melting line of vortex line lattices
We develop a theory for dislocation-mediated structural transitions in the
vortex lattice which allows for a unified description of phase transitions
between the three phases, the elastic vortex glass, the amorphous vortex glass,
and the vortex liquid, in terms of a free energy functional for the dislocation
density. The origin of a critical endpoint of the melting line at high magnetic
fields, which has been recently observed experimentally, is explained.Comment: 4 pages, 1 figur
Glide and Superclimb of Dislocations in Solid He
Glide and climb of quantum dislocations under finite external stress,
variation of chemical potential and bias (geometrical slanting) in Peierls
potential are studied by Monte Carlo simulations of the effective string model.
We treat on unified ground quantum effects at finite temperatures . Climb at
low is assisted by superflow along dislocation core -- {\it superclimb}.
Above some critical stress avalanche-type creation of kinks is found. It is
characterized by hysteretic behavior at low . At finite biases gliding
dislocation remains rough even at lowest -- the behavior opposite to
non-slanted dislocations. In contrast to glide, superclimb is characterized by
quantum smooth state at low temperatures even for finite bias. In some
intermediate -range giant values of the compressibility as well as
non-Luttinger type behavior of the core superfluid are observed.Comment: Updated version submitted to JLTP as QFS2010 proceedings; 11 pages, 6
figure
Effect of electron irradiation on vortex dynamics in YBa_2Cu_3O_{7-x} single crystals
We report on drastic change of vortex dynamics with increase of quenched
disorder: for rather weak disorder we found a single vortex creep regime, which
we attribute to a Bragg-glass phase, while for enhanced disorder we found an
increase of both the depinning current and activation energy with magnetic
field, which we attribute to entangled vortex phase. We also found that
introduction of additional defects always increases the depinning current, but
it increases activation energy only for elastic vortex creep, while it
decreases activation energy for plastic vortex creep.Comment: 4 pages, 3 figures, submited to Phys. Rev.
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