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in subjects: "Cubic Lattices"

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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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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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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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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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Evaluation of anelastic evidence for interstitial solute binding in bcc metals

A Direct Spectrum Analysis (DSA) technique has been applied to key internal friction and elastic after-effect data which are involved in the controversy over the existance of interstitial clustering in the refractory metals. It is found that at relatively high interstitial solute concentrations some of the Snoek peak broadening is due to relaxations that are distinct from the main relaxation. This finding supports the view that interstitial solutes have an interaction that produces clusters of … more

Date: 1985

Creator: Cost, J. R. & Stanley, J. T.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Effective-cluster simulation of polycrystal plasticity

A model is proposed in which each grain, representative of a certain orientation and strength, is embedded in a thin shell of plastic effective medium; this assembly is called an ''effective cluster''. For each grain, the plastic strain increment is chosen such that the yield surface of the effective cluster gives the macroscopic stress. The results differ from uniform-strain theories only in some cases, such as in the compression of f.c.c. polycrystals, where ''grain curling'' occurs.

Date: January 1, 1985

Creator: Kocks, U. F.; Tome, C. & Canova, G. R.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Environmental reactions and their effects on mechanical behavior of metallic materials. Technical progress report, February 1, 1977--January 31, 1978

New results obtained in surface oxide softening of the Group VB refractory metals and mechanical behavior of Nb-H and Nb-D alloys are presented. The results include: (a) experimental verification of a model of surface oxide softening of body-centered cubic metals; (b) determination of a stress-differential effect in surface oxide softening; and (c) characterization of hydrogen and deuterium strengthening in Nb and Nb-O alloys. The second section reviews major contributions in topics on: interst… more

Date: September 30, 1977

Creator: Gibala, R.; Sethi, V. K. & Fournier, R.

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Magnetic Susceptibility and Proton NMR study of TiCr/sub 1/ /sub 8/H/sub x/

The electronic properties of the hexagonal (C-14) and cubic (C-15) allotropes of the TiCr/sub 1/ /sub 8/+/sub 0/ /sub 1//H/sub 2/ system have been examined via magnetic susceptibility and proton NMR studies. The results indicate an increase in N(E/sub F/), the electron density of states at the Fermi level, with increasing H/M for both allotropes; the trend extends into the ..cap alpha..'-hydride phase. The results suggest a basis for thermodynamic anomalies reported for the solution of hydrogen… more

Date: January 1, 1982

Creator: Lynch, J. F.; Johnson, J. R. & Bowman, R. C., Jr.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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First-principles calculation of the magnetic properties of paramagnetic fcc iron

Using the disordered local moment picture of itinerant magnetism, we present calculations of the temperature and volume dependence of the magnetic moment and spin-spin correlations for fcc Fe in the paramagnetic state. These calculations are based on the parameter-free, first principles approach of local spin density functional theory and the coherent potential approximation is used to treat the disorder associated with the random orientation of the local moments.

Date: January 1, 1985

Creator: Johnson, D. D.; Gyorffy, B. L.; Pinski, F. J.; Staunton, J. & Stocks, G. M.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Body-centered cubic ion correlation experiment

The results of an interlaboratory correlation experiment involving eight laboratory sites studying the ion irradiation of molybdenum are presented. The program was comprised of three parts. The first part compared the radiation damage produced in a reference specimen of molybdenum by ions of different masses and different energies. The second part of the program compared measurements on a common micrograph supplied to all participants in the program. The results from all the sites agreed very w… more

Date: April 1, 1977

Creator: Brimhall, J.L. (comp.)

Item Type: Report

Partner: UNT Libraries Government Documents Department

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Cluster expansion of fcc Pd-V intermetallics

A cluster expansion is used to compute fcc ground states from first principles for the Pd-V system. Intermetallic structures are not assumed but derived rigorously by minimizing the configurational energy subject to linear constraints. A large number of concentration-independent interactions are calculated by the method of direct configurational averaging. Agreement with the fcc-based portion of the experimentally-determined Pd-V phase diagram is quite satisfactory. 25 refs., 2 figs.

Date: June 1, 1991

Creator: de Fontaine, D.; Wolverton, C.; Ceder, G. (Lawrence Berkeley Lab., CA (United States)) & Dreysse, H. (Nancy-1 Univ., 54 (France). Lab. de Physique du Solide)

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Energy parameters and crystal field effects in the mixed valence problem: chemically collapsed cerium

Previous neutron scattering studies of the mixed valence state in rare earth systems failed to reveal the presence of crystal electric field (CEF) effects. In cases studied, the characteristic charge fluctuation energies were comparable to the expected CEF energies. A system was designed in which it is possible to systematically vary the charge fluctuation energy E/sub c/ from the regime E/sub c/ approx. ..delta.. to E/sub c/ << ..delta.., where ..delta.. is the characteristic CEF energy. Resul… more

Date: January 1, 1979

Creator: Parks, R.D.; Shapiro, S.M.; Majkrzak, C.F. & Grier, B.H.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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New look at the atomic volumes of the. beta. -form of the transplutonium metals

The atomic volumes of the beta-form of the first four transplutonium metals were evaluated using data for samples prepared by thermal and by pressure treatment. The volumes derived for curium, berkelium, and californium metals quenched from elevated temperatures were found to be consistently larger than those for ''pressure-quenched'' samples, whose volumes were in good agreement with values for the alpha-forms. The cubic lattice parameters from ''pressure-quenched'' samples also provided a mor… more

Date: January 1, 1986

Creator: Haire, R.G.; Benedict, U.; Peterson, J.R.; Dufour, C. & Dabos, S.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Quantitative Prediction of Surface Segregation in Bimetallic Pt-MAlloy Nanoparticles (M=Ni, Re, Mo)

This review addresses the issue of surface segregation inbimetallic alloy nanoparticles, which are relevant to heterogeneouscatalysis, in particular for electro-catalysts of fuel cells. We describeand discuss a theoretical approach to predicting surface segregation insuch nanoparticles by using the Modified Embedded Atom Method and MonteCarlo simulations. In this manner it is possible to systematicallyexplore the behavior of such nanoparticles as a function of componentmetals, composition, and … more

Date: June 20, 2005

Creator: Wang, Guofeng; Van Hove, Michel A.; Ross, Phil N. & Baskes,Michael I.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Photoelectron Diffraction of Magnetic Ultrathin Films: Fe/Cu(001)

The preliminary results of an ongoing investigation of Fe/Cu(001) are presented here. Energy dependent photoelectron diffraction, including the spin-dependent variant using the multiplet split Fe3s state, is being used to investigate the nanoscale structures formed by near-monolayer deposits of Fe onto Cu(001). Core-level photoemission from the Fe3p and Fe3s states has been generated using synchrotron radiation as the tunable excitation source. Tentatively, a comparison of the experimental Fe3p… more

Date: January 3, 1991

Creator: Tobin, J.G. (Lawrence Livermore National Lab., CA (USA)); Wagner, M.K. (Wisconsin Univ., Madison, WI (USA). Dept. of Chemistry); Guo, X.Q. & Tong, S.Y. (Wisconsin Univ., Milwaukee, WI (USA). Dept. of Physics)

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Cracking behavior of cored structures

The effects of compositional gradients, are considered based on a thermodynamic analysis, referred to as the Cahn-Hillard analysis, which describes the degree to which a local surface energy is modified by the presence of a composition gradient. The analysis predicts that both ductile and brittle fracture mechanisms are enhanced by the presence of a composition gradient. Data on stress corrosion cracking and fatigue crack growth in selected FCC alloys are used to illustrate the significance of … more

Date: September 1991

Creator: Wahid, A.; Olson, D.L.; Matlock, D.K. (Colorado School of Mines, Golden, CO (United States). Center for Welding and Joining Research) & Kelly, T.J. (General Electric Aircraft Engines, Evendale, OH (United States))

Item Type: Thesis or Dissertation

Partner: UNT Libraries Government Documents Department

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Structural damage in a self-irradiated zirconolite-based ceramic

The zirconolite phase of SYNROC nuclear waste was fabricated with 5 mol % /sup 238/PuO/sub 2/ substituted for a like amount of ZrO/sub 2/, in order to induce self-irradiation damage. The resulting product exhibited a matrix of monoclinic zirconolite containing approx. 3.8 mol % PuO/sub 2/ along with roughly 20 vol % of the cubic polymorph with approximately twice the PuO/sub 2/ content of the matrix. After a dose of 2.1 x 10/sup 25/ ..cap alpha.. decays/m/sup 3/ at room temperature (800 days' s… more

Date: January 1, 1983

Creator: Clinard, F.W. Jr.; Rohr, D.L. & Roof, R.B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Shock anomaly and s-d transition in high-pressure lanthanum

Linear-muffin-tin orbital calculations of the band structure and pressure-volume isotherms for fcc La, both at zero and finite temperatures. The calculated bulk modulus shows a rapid stiffening in the range from 40 to 50% compression, due to termination of the 6s to 5d electronic transition. When combined with a simple Slater model analysis, these results yield a temperature dependent peak in the lattice Grueneisen parameter. Experimental confirmation of this peak is found in an anomalous stiff… more

Date: July 23, 1981

Creator: McMahan, A.K.; Skriver, H.L. & Johansson, B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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High rate sputter deposition of wear resistant tantalum coatings

The refractory nature and high ductility of body centered cubic (bcc) phase tantalum makes it a suitable material for corrosion- and wear-resistant coatings on surfaces which are subjected to high stresses and harsh chemical and erosive environments. Sputter deposition can produce thick tantalum films but is prone to forming the brittle tetragonal beta phase of this material. Efforts aimed at forming thick bcc phase tantalum coatings in both flat plate and cylindrical geometries by high-rate tr… more

Date: November 1, 1991

Creator: Matson, D. W.; Merz, M. D. & McClanahan, E. D.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Synthesis of the monoclinic yttria by thermal plasma processing

Submicron powders of monoclinic yttria were prepared by thermal plasma processing of commercial yttria powder. The starting yttria powder was vaporized in the hot tail flame of a thermal argon plasma and the resulting vapor was quenched with hydrogen gas to form yttria particles with a 21-nm mean diameter. The synthesis of yttria by oxidizing yttrium carbide in the plasma was also examined. The plasma powders were characterized by powder x-ray diffraction, transmission electron microscopy, and … more

Date: January 1, 1987

Creator: Vogt, G.J.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Alpha decay self-damage in cubic and monoclinic zirconolite

Samples of primarily-monoclinic /sup 238/Pu-doped zirconolite were stored at ambient temperature to allow accumulation of alpha decay self-damage to a dose of 1 x 10/sup 24/ ..cap alpha../m/sup 3/ (equivalent to a SYNROC age of approx. 10/sup 3/y). Bulk swelling reached 2.3 vol% with no tendency toward saturation, a damage response similar to that observed for cubic Pu-doped zirconolite. X-ray volumetric swelling at 4 x 10/sup 24/ ..cap alpha../m/sup 3/ was 1 vol%, considerably less than that f… more

Date: January 1, 1981

Creator: Clinard, F.W. Jr.; Land, C.C.; Peterson, D.E.; Rohr, D.L. & Roof, R.B.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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Barium potassium bismuth oxide: Synthesis and physical properties

A series of compounds Ba/sub 1/minus/x/K/sub x/BiO/sub 3/ have been prepared and characterized over the range of compositions ranging from x = 0.3 to 0.5. A neutron powder diffraction analysis has been carried out for the composition x = 0.4 at room temperature and at 10 K. Examination of the superconducting properties as a function of x indicates superconductivity occurs over a narrow range of compositions close to x = 0.4, with T/sub c/ of 29 K. Specific heat measurements indicate conventiona… more

Date: January 1, 1989

Creator: Ott, K. C.; Hundley, M. F.; Kwei, G. H.; Maley, M. P.; McHenry, M. E.; Peterson, E. J. et al.

Item Type: Article

Partner: UNT Libraries Government Documents Department

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The electronic structure of grain boundaries in Nb

We present first-principles calculations of the electronic structure of Nb grain boundaries. These are the first such calculations for a bcc metal using the real-space multiple-scattering theory (RSMST). Local densities of states near a {Sigma}5 twist grain boundary are compared to those for bulk Nb. 5 refs., 1 fig.

Date: November 1, 1990

Creator: Sowa, E.C.; Gonis, A. (Lawrence Livermore National Lab., CA (USA)) & Zhang, X.G. (Lawrence Berkeley Lab., CA (USA))

Item Type: Article

Partner: UNT Libraries Government Documents Department