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in subjects: "Crystal Lattices"

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Rigid muffin-tin approximation for the electron-phonon interaction in transition metals

Progress in calculating the electron-phonon parameters of transition metals has been based on either the rigid muffin-tin approximation (RMTA) or the fitted modified tight-binding approximation (FMTBA). The RMTA has been shown to be remarkably accurate for average electron-phonon properties, but there are indications that RMTA matrix elements may be too small at low momentum transfer. An attempt is made to demonstrate these assertions concerning the accuracy of RMTA and the numerous electron-ph… more

Date: January 1, 1980

Creator: Butler, W. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Theory of ordering transformations in metals and minerals

This dissertation presents an investigation of ordering in FCC based systems using the pair potential approximation in the ground state and mean field limits. The theoretical approach is used to explain the occurrence of observed equilibrium phases and characteristics of thermodynamic instabilities, in particular, spinodal ordering and decomposition. It is shown that the stability of non-integer domain sizes in long period superstructures such as Al{sub 3}Ti and Ag{sub 3}Mg may result from the … more

Date: July 1, 1991

Creator: Lindsey, Timothy Francis

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

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Devil's staircase and order without periodicity in classical condensed matter

The existence of incommensurate structures proves that crystal ordering is not always the most stable one for nonquantum matter. Some properties of structures which are obtained by minimizing a free energy are investigated in the Frenkel Kontorova and related models. It is shown that an incommensurate structure can be either quasi-sinusoidal with a phason mode or built out of a sequence of equidistant defects (discommensurations) which are locked to the lattice by the Peierls force. In that sit… more

Date: January 1, 1982

Creator: Aubry, S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Microscopic theory of charges density wave instability in NbSe/sub 2/

The microscopic theory of Sinha and Harmon for electronically driven lattice instabilities is used to explain the ''Kohn-like'' anomalies in the ..sigma../sub 1/ phonon branch and the observed incommensurate superlattice Bragg peak in 2H-NbSe/sub 2/, characteristic of the charge density wave at low temperatures in the neutron scattering experiments of Moncton et al. In accordance with the APW and LCAO band-structure calculations of Mattheiss of 2H-NbSe/sub 2/, the presence o… more

Date: January 1, 1977

Creator: Das, S G; Sinha, S K & Wakabayashi, N

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Existence of fcc TiCr/sub 1/ /sub 8/H/sub 5/ /sub 3/

Originally an orthorhombic structure was assigned to the non-stoichiometric hydride TiCr/sub 1/ /sub 8/H/sub 3/ /sub 6/. Recent neutron and x-ray diffraction data indicated, however, that an alternate interpretation was possible, i.e. the solid consists of two hydride phases, an ..cap alpha..' Laves phase having a composition of TiCr/sub 1/ /sub 8/H/sub 2/ /sub 8/ and an fcc phase with a much higher hydrogen content. This proved to be the case and it has been determined that the high concentrat… more

Date: February 1, 1982

Creator: Johnson, J. R.; Reilly, J. J.; Reidinger, F.; Corliss, L. M. & Hastings, J. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Electronic and structural properties of metallic microclusters

The first part of this thesis presents a first-order pseudopotential calculation at T=O of the total energy of small sodium clusters of size N<800. The calculation is based on a local-pseudopotential scheme and local-density correlation and exchange. A temperature-size (T-N) phase-diagram is then derived using the T=O results and Lindemann's criterion for melting. The phase-diagram contains three regions of stability: (1) a liquid (jellium) phase at temperatures above the melting line T{sub M}(… more

Date: April 1, 1992

Creator: Maiti, A.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Low lying defect mode in CaF/sub 2/:Y/sup 3 +/. [Measurements to 6. 5 kbars at 4. 2/sup 0/K]

No Description Available.

Date: February 1, 1975

Creator: Campbell, J. A.; Schiff, E. A. & Sievers, A. J.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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High strain rate deformation in FCC metals and alloys

The effect of strain rate, and particularly of high strain rates, on deformation mechanisms in materials is of fundamental interest to those who model and analyze dynamic loading. In many materials the strain rate sensitivity is known to increase dramatically when the strain rate is raised above approx.10/sup 3/ s/sup -1/. This increase has been interpreted previously as a transmission in deformation mechanism from thermal activation control at low strain rate to dislocation drag control at hig… more

Date: January 1, 1985

Creator: Follansbee, P.S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Correlation theory applied to the static and dynamic properties of EuO and EuS

The paramagnetic scattering was recently measured for EuO. It was found that spin-wave-like excitations develop for wave vectors approaching the zone boundary. The spectrum was found to be well described by damped harmonic oscillators (also called the two-pole-approximation). This approximation was used previously in the correlation theory primarily to calculate static properties. Selfconsistent dynamic and static calculations have been performed for EuO, which is an ideal Heisenberg magnet wit… more

Date: October 1, 1981

Creator: Lindgard, P.A.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Vibrational relaxation and energy transfer of matrix isolated HCl and DCl

Vibrational kinetic and spectroscopic studies have been performed on matrix-isolated HCl and DCl between 9 and 20 K. Vibrational relaxation rates for v = 2 and v = 1 were measured by a tunable infrared laser-induced, time-resolved fluorescence technique. In an Ar matrix, vibrational decay times are faster than radiative and it is found that HCl relaxes about 35 times more rapidly than CCl, in spite of the fact that HCl must transfer more energy to the lattice than DCl. This result is explained … more

Date: December 1, 1977

Creator: Wiesenfeld, J.M.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Scattering of phonons by dislocations

By 1950, an explicit effort had been launched to use lattice thermal conductivity measurements in the investigation of defect structures in solids. This technique has been highly successful, especially when combined with the measurements of other properties such as optical absorption. One exception has been the study of dislocations. Although dislocations have a profound effect on the phonon thermal conductivity, the mechanisms of the phonon-dislocation interaction are poorly understood. The mo… more

Date: January 1, 1979

Creator: Anderson, A. C.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Mossbauer effect and neutron diffraction study of the anomalous lattice behavior of U/sub 6/Fe

Neutron diffraction and /sup 57/Fe Moessbauer effect measurements have been made on the exchange-enhanced superconductor U/sub 6/Fe. The neutron diffraction results indicate a pronounced anisotropy in the thermal expansion of the unit cell and an anomalous temperature dependence for the c-axis component of the total Debye-Waller factor of Fe below 100K. The Moessbauer effect measurements show non-Debye behavior in the mean-squared displacement of Fe, with phonon hardening occurring below 100K. … more

Date: June 1, 1985

Creator: Vaishnava, P. P.; Dwight, A. E.; Kimball, C. W.; Jorgensen, J. D. & Fradin, F. Y.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Interactions between small-polaronic particles in solids

When a light particle in a solid composed of relatively heavy atoms is associated with substantial displacements of the equilibrium positions of the atoms immediately surrounding it, the composite entity may be regarded as being small polaronic. Many instances of self-trapping of electronic charge carriers, excitons and light atoms such as hydrogen are known. A significant contribution to the interaction between such particles results from interference between their atomic displacement patterns… more

Date: January 1, 1980

Creator: Emin, D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Studies of the strain-dependent properties of A15 filamentary conductors at Brookhaven National Laboratory

Work at BNL pertaining to the strain response of filamentary bronze-processed superconductors is reviewed. This work includes the intrinsic strain dependence of the critical properties of A15 structure compounds, the nature of the initial internal strain state of composite conductors, and the interplay between these residual strains and applied strains which governs the response of the conductor to external strain. Some factors which can enhance the strain tolerances of filamentary conductors a… more

Date: January 1, 1980

Creator: Luhman, T & Welch, D O

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Study of radiation damage in metals by positron annihilation. [Neutron irradiation]

Positron annihilation is a sensitive technique for probing defects in metals and it has recently been shown to be a valuable tool for the study of radiation damage. After an introduction to the three basic experimental methods (angular correlation, Doppler broadening, and lifetime measurements), the interaction of positrons with lattice defects is reviewed. Results for the annealing of damage after low temperature irradiation are used to show that positron annihilation has provided new informat… more

Date: January 1, 1977

Creator: Gauster, W.B

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Pion Condensation in a Field Theory Consistent with Bulk Properties of Nuclear Matter

No Description Available.

Date: May 1, 1980

Creator: Banerjee, B.; Glendenning, N.K. & Gyulassy, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Theory of the temperature dependence of positron bulk lifetimes-implications for vacancy formation enthalpy measurements via positron experiments

Temperature dependent effects, which may have a bearing on determinations of vacancy formation enthalpies in metals by positron annihilation, have been observed in certain metals. These effects have been observed to occur both at temperatures below those at which positron annihilation is most sensitive to equilibrium vacancies and at temperatures well within the vacancy-sensitive region. The effect of thermal lattice displacements on positron lifetimes in metals was investigated to help underst… more

Date: February 1, 1977

Creator: Tam, S.W.; Sinha, S.K. & Siegel, R.W.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Crystal defect studies using x-ray diffuse scattering

Microscopic lattice defects such as point (single atom) defects, dislocation loops, and solute precipitates are characterized by local electronic density changes at the defect sites and by distortions of the lattice structure surrounding the defects. The effect of these interruptions of the crystal lattice on the scattering of x-rays is considered in this paper, and examples are presented of the use of the diffuse scattering to study the defects. X-ray studies of self-interstitials in electron … more

Date: January 1, 1980

Creator: Larson, B. C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Some non-linear physics in crystallographic structures

A summary of studies on simple but strongly nonlinear crystallographic models that make use of some methods in stochasticity is presented. Two one-dimensional models are described; one has been studied to understand some aspects of the nonlinear dynamics in crystals when close to the transition temperature, the other is for commensurability and incommensurability problems. Periodic orbits and the dynamics of a one-dimensional coupled double-well chain are considered, along with lattice locking … more

Date: October 1, 1977

Creator: Aubry, S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Structure of ordered alloys

Recent progress in studying ordered alloys by lattice fringe imaging is reviewed. Firstly the optimum experimental conditions for producing images suitable for interpretation are outlined. Secondly lattice and conventional imaging are compared and the advantages of the former for obtaining atomic level detail and compositional estimates are described. Finally some important results from this program are discussed, particularly the evidence for a microdomain model of short-range order and the fi… more

Date: August 1, 1977

Creator: Sinclair, R. & Thomas, G.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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A15 multifilamentary superconductors by the infiltration process

The inherent brittleness of the A15 compounds, and the requirement for a filamentary morphology, led to a heavy reliance on a powder approach for the preparation of superconducting tapes and wires. The quench-age technique, a non-powder process, was employed for the niobium-aluminum system, following the special features of the equilibrium phase diagram. The powder approach proved particularly effective for binaries, such as Nb-Sn, and for the ternaries Nb(Al,Ge) and Nb(Al,Si). Two variations o… more

Date: May 1, 1980

Creator: Pickus, M.R.; Holthuis, J.T. & Rosen, M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Applications of pulsed neutron powder diffraction to actinide elements. [Pu-Al]

We have been using the technique of pulsed neutron powder diffraction to study several problems in the physics and chemistry of the actinide elements. In these elements one often encounters very complex structures resulting from polymorphic transformations presumably induced by the presence of 5f-electrons. For example, at least five distinct structures of plutonium metal are found between room temperature and its melting point of 640/sup 0/C, and two of the structures are monoclinc. The determ… more

Date: November 1, 1987

Creator: Lawson, A. C.; Richardson, J. W.; Mueller, M. H.; Lander, G. H.; Goldstone, J. A.; Williams, A. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Electronic structure of nonstoichiometric cubic hydrides

Using the supercell approach we have calculated the electronic structure of Y/sub 4/H/sub 8/, Y/sub 4/H/sub 9/, Y/sub 4/H/sub 11/, and Y/sub 4/H/sub 12/ as prototypic of nonstoichiometric cubic di- and trihydrides. The nature of the interaction between the yttrium and the octahedral and tetrahedral hydrogens is shown by the relative amount of charge contained in the crystal spheres. Each added hydrogen lowers one band which was already partially filled. The charge on both the octahedral and tet… more

Date: January 1, 1980

Creator: Switendick, A.C.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Lattice expansion as a measure of surface segregation and solubility of hydrogen in. cap alpha. -FeTiH/sub x/

The lattice expansion of ..cap alpha..-FeTiH/sub x/ was found to be anomalously small as a function of hydrogen content. The apparent partial molar volume of hydrogen, anti V/sub H/, was 0.1 +- 0.1 cc/g atom (FeTiH/sub <0.03/), a value much lower than the accepted range of 2.2 to 1.4 cc/g atom previously reported for hydrogen-metal solutions. The behavior is attributed to preferential occupation by hydrogen of Ti rich sites produced by surface segregation effects which are known to occur in act… more

Date: January 1, 1980

Creator: Reilly, J. J.; Johnson, J. R.; Reidinger, F.; Lynch, J. F.; Tanaka, J. & Wiswall, R. H.

Item Type: Article

Partner: UNT Libraries Government Documents Department