Quantum diffusion: effect of defect-localized phonon dynamics (original) (raw)
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The phonon transport in crystals with heavy defects
Physica B: Condensed Matter, 1995
The problem of phonon transport in crystals with heavy defects is studied. A nontriviai behavior of the phonon diffusion coefficient near the quasilocal frequency concerned with the dwell effect is found. Two independent approaches the diagrammatic and kinetic ones-are proposed.
Process of phonon diffusion through crystalline structures
Nauka, bezbednost, policija
Instead of usual approach, applying displacement-displacement Green's functions, the momentum-momentum Green's functions will be used to calculate the diffusion tensor. These functions enter into Kubo's formula defining diffusion properties of the system. Calculation of the diffusion tensor requires solving of the system of difference equations. It is shown that the elements of the diffusion tensor express discrete behaviour of the dispersion law of elementary excitations and, more important-that they are temperature independent.
Adequacy of lattice dynamics for high-temperature point-defect properties
Physical review, 1986
Comparison arith existing Monte Carlo and molecular-dynamics data of novel quasiharmonic lattice-dynamics {LD)calculations for formation and migration of lattice vacancies in rare-gas crystals at melting shows that the effect of residual anharmonirity on atomic diffusion is not large. Inclusion of vibrational contributions to the free energy and pressure ensures, for the first time, thermodynamic consistency bet&veen LD results at constant volume, pressure, and lattice sparing. Lattice-statics predictions are badly in error. Constant-volume defect entropies are negative and surprisingly large.
Quantum Diffusion of Impuritons in the Gas of Phonons in Quantum Mixtures of Helium Isotopes
1998
The system of kinetic equations for distribution functions of impurity excitations in solid 3 He-4 He mixtures in the presence of phonons is solved. The results obtained allows us to calculate the spin diffusion coefficient of 3 He-4 He quantum crystals. The found expression differs from the results of the previous theoretical studies. A comparison of the obtained diffusion coefficient with experimental data makes it possible to determine the numerical values of the energy band width of impurity excitations.
Nanomaterials, 2020
A canonical quantization procedure is applied to the interaction of elastic waves—phonons—with infinitely long dislocations that can oscillate about an equilibrium, straight line, configuration. The interaction is implemented through the well-known Peach–Koehler force. For small dislocation excursions away from the equilibrium position, the quantum theory can be solved to all orders in the coupling constant. We study in detail the quantum excitations of the dislocation line and its interactions with phonons. The consequences for the drag on a dislocation caused by the phonon wind are pointed out. We compute the cross-section for phonons incident on the dislocation lines for an arbitrary angle of incidence. The consequences for thermal transport are explored, and we compare our results, involving a dynamic dislocation, with those of Klemens and Carruthers, involving a static dislocation. In our case, the relaxation time is inversely proportional to frequency, rather than directly pro...
Quantum diffusion in transition metals
Journal of the Less …, 1991
The functions governing the temperature dependence of small-polaron diffusion are calculated by using the phonon dispersion relations with high accuracy for octahedral interstitial sites in copper, palladium, nickel and platinum f.c.c. hosts, as well as for tetrahedral and octahedral sites in tantalum, niobium and vanadium hosts. The current experimental data on the diffusion coefficient for hydrogen in b.c.c. tantalum and niobium, and for positive muons in copper are very well reproduced for all temperature ranges. By comparison with exact calculation, very accurate results are also obtained by using an approximate universal function calculated within the Debye approximation, for which we give a closed analytical formula. This allows manual calculations of the diffusion coefficient for light interstitial impurities in transition metals within the small-polaron model.
Classical Mobility of Highly Mobile Crystal Defects
Physical Review Letters, 2014
Highly mobile crystal defects such as crowdions and prismatic dislocation loops exhibit an anomalous temperature independent mobility unexplained by phonon scattering analysis. Using a projection operator, without recourse to elasticity, we derive analytic expressions for the mobility of highly mobile defects and dislocations which may be efficiently evaluated in molecular dynamics simulation. The theory explains how a temperature-independent mobility arises because defect motion is not an eigenmode of the Hessian, an implicit assumption in all previous treatments.
Lattice Dynamics: Phonon Relaxation
Springer Series in Chemical Physics, 2014
• Frequency of lattice vibration fingerprints the stiffness (Yd) of a peculiarly representative bond in real space in the form of x µ z/d(E/l) 1/2 µ (Yd) 1/2 with involvement of the bond order (z), bond length (d), bond energy (E), and the reduced mass of a dimer. • The process of phonon scattering contributes less to the intrinsic vibration. • Atomic undercoordination softens the optical phonons of nanostructures. • Intergrain interaction results in emerging of the low-frequency phonons whose frequency undergoes blueshift with reduction in solid size. • The D and 2D modes in carbon arise from interaction of a certain atoms with all of its z neighbors; while the G mode in carbon and the E g mode (144 cm-1) in TiO 2 are dominated by dimer interaction only.
An observable for vacancy characterization and diffusion in crystals
The Journal of Chemical Physics, 2013
To locate the position and characterize the dynamics of a vacancy in a crystal, we propose to represent it as the ground state density of a pseudo-quantum probe particle associated to the Hamiltonian which has, for the potential energy, the field generated by the atoms in the sample. In this description, the coefficient of the kinetic energy term is a tunable parameter controlling the density localization in the regions of the relevant minima of the potential energy field. Based on this description, we derive a set of collective variables that we use in rare event simulations to identify some of the vacancy diffusion paths in a 2D crystal. Our simulations reveal that the vacancy migrates according to local and nonlocal mechanisms, the second involving several lattice sites and producing a long range migration. We also observed a vacancy induced crystal reorientation process.