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Positron-annihilation 2D-ACAR studies of disordered and defected alloys

Description: Theoretical and experimental progess in connection with 2D-ACAR positron annihilation studies of ordered, disordered, and defected alloys is discussed. We present, in particular, some of the recent developments concerning the electronic structure of disordered alloys, and the work in the area of annihilation from positrons trapped at vacancy-type defects in metals and alloys. The electronic structure and properties of a number of compounds are also discussed briefly; we comment specifically on … more
Date: September 1, 1987
Creator: Bansil, A.; Prasad, R.; Smedskjaer, L. C.; Benedek, R. & Mijnarends, P. E.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Ferromagnetism in tetragonally distorted LaCoO3 thin films

Description: Thin films of epitaxial LaCoO{sub 3} were synthesized on SrTiO{sub 3} and (La, Sr)(Al, Ta)O{sub 3} substrates varying the oxygen background pressure in order to evaluate the impact of epitaxial growth as well as oxygen vacancies on the long range magnetic order. The epitaxial constraints from the substrate impose a tetragonal distortion compared to the bulk form. X-ray absorption and x-ray magnetic circular dichroism measurements confirmed that the ferromagnetism arises from the Co ions and per… more
Date: September 17, 2008
Creator: Mehta, Virat Vasav; Liberati, Marco; Wong, Franklin J.; Chopdekar, Rajesh Vilas; Arenholz, Elke & Suzuki, Yuri
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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MOLECULAR DYNAMICS SIMULATIONS OF DISPLACEMENT CASCADES IN MOLYBDENUM

Description: Molecular dynamics calculations have been employed to simulate displacement cascades in neutron irradiated Mo. A total of 90 simulations were conducted for PKA energies between 1 and 40 keV and temperatures from 298 to 923K. The results suggest very little effect of temperature on final defect count and configuration, but do display a temperature effect on peak defect generation prior to cascade collapse. Cascade efficiency, relative to the NRT model, is computed to lie between 1/4 and 1/3 in a… more
Date: September 8, 2003
Creator: Smith, Richard Whiting
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Atomic-defect mechanisms for diffusion in refractory bcc metals

Description: Despite a number of recent investigations into the nature and properties of equilibrium atomic defects in the refractory bcc metals, the mechanisms responsible for the high-temperature mass transport in these materials are not clear. The observed strong high-temperature enhancement in self-diffusion appears to be unexplainable in terms of divacancies, but might result from the presence of small equilibrium concentrations of highly-mobile self-interstitials. Recent vacancy formation measurements… more
Date: September 1, 1986
Creator: Siegel, R. W.; Mundy, J. N. & Smedskjaer, L. C.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Electronic structure of metals and semiconductors: bulk, surface, and interface properties

Description: A theoretical study of the electronic structure of various metals and semiconductors is presented with the emphasis on understanding the properties of these materials when they are subjected to extreme conditions and in various different configurations. Among the bulk systems studied, the properties of cesium under high pressure are discussed in terms of the electronic structure calculated at various cell volumes using the pseudopotential method. Local fields or umklapp processes in semiconduct… more
Date: September 1, 1976
Creator: Louie, S. G. S.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Divacancy-hydrogen complexes in dislocation-free high-purity germanium. [Annealing, Hall effect, steady-state concentration energy dependence]

Description: A defect center with a single acceptor level at E/sub v/ + 0.08 eV appears in H/sub 2/-grown dislocation-free high-purity germanium. Its concentration changes reversibly upon annealing up to 650 K. By means of Hall-effect and conductivity measurements over a large temperature range the temperature dependence of the steady-state concentration between 450 and 720 K as well as the transients following changes in temperature were determined. The observed acceptor level is attributed to the divacanc… more
Date: September 1, 1976
Creator: Haller, E. E.; Hubbard, G. S.; Hansen, W. L. & Seeger, A.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Influence of point defects on grain boundary motion.

Description: This work addresses the influence of point defects, in particular vacancies, on the motion of grain boundaries. If there is a non-equilibrium concentration of point defects in the vicinity of an interface, such as due to displacement cascades in a radiation environment, motion of the interface to sweep up the defects will lower the energy and provide a driving force for interface motion. Molecular dynamics simulations are employed to examine the process for the case of excess vacancy concentrat… more
Date: September 1, 2010
Creator: Foiles, Stephen Martin
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Development of Nanoscale Ceramics for Advanced Power Applications

Description: Bulk structures of unstabilized ZrO{sub 2-x}, with x in the range of 0 {<=} x {<=} 0.44, at ambient pressure have been found to exist in three different structures. (monoclinic, tetragonal and cubic.). At ambient temperature and elevated pressures above 3.5 GPa, unstabilized zirconia at these same compositions is found as a fourth phase, the orthorhombic phase. Work done in this project has demonstrated that nanoscale zirconia particles containing the orthorhombic phase in addition to amo… more
Date: September 30, 1999
Creator: Leffler, Miriam & Helble, Joseph
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Density-functional-theory results for Ga and As vacancies in GaAs obtained using the Socorro code.

Description: The Socorro code has been used to obtain density-functional theory results for the Ga vacancy (V{sub Ga}) and the As vacancy (V{sub As}) in GaAs. Calculations were performed in a nominal 216-atom simulation cell using the local-density approximation for exchange and correlation. The results from these calculations include: (1) the charge states, the atomic configurations of stable and metastable states, (2) energy levels in the gap, and (3) activation energies for migration. Seven charge states… more
Date: September 1, 2009
Creator: Wright, Alan Francis
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Layered manganese oxide intergrowth electrodes for rechargeable lithium batteries: Part 1-substitution with Co or Ni

Description: Lithium manganese oxides substituted with nickel or cobalt were characterized electrochemically in lithium cell configurations. The compounds studied were either single-phase layered structures with either primarily O2 or O3 stacking arrangements, or O2/O3 intergrowths, prepared from P2, P3 and P2/P3 sodium-containing precursors, respectively. The stacking arrangements are extremely sensitive to the Na/T. M. (T. M. = transition metal) ratios and the level of substitution. Phase diagrams showing… more
Date: September 8, 2004
Creator: Dolle, Mickael; Patoux, Sebastien & Doeff, Marca M.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Review of the thermal conductivity of nuclear graphite under HTGR conditions

Description: Experimental data on the thermal conductivity of needle-coke and isotropic graphites irradiated between 500 and 1600 deg C are reviewed. Irradiation reduces the room-temperature thermal conductivity; as the fluence increases, the rate of reduction declines and the conductivity approaches a saturation level which increases as the irradiation temperature increases. Eventually, when irradiation-induced expansion starts, the conductivity again decreases. The time constant for approach to saturation… more
Date: September 1, 1973
Creator: Price, R.J.
Item Type: Refine your search to only Report
Partner: UNT Libraries Government Documents Department
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Contacts for high-resistivity (Cd,Mn)Te crystals

Description: Semi-insulating (Cd,Mn)Te crystals offer a material that may compete well with the commonly used (Cd,Zn)Te crystals for manufacturing large-area X- and gamma-ray detectors. The Bridgman growth method yields good quality, high-resistivity (10{sup 9} - 10{sup 10} {Omega} {center_dot} cm) crystals of (Cd,Mn)Te:V. Doping the as-grown crystals with the compensating agent vanadium ({approx} 10{sup 16} cm{sup -3}) ensures their high resistivity; thereafter, annealing them in cadmium vapors reduces the… more
Date: September 9, 2010
Creator: Witkowska-Baran, M.; James, R.; Mycielski, A.; Kochanowska, D.; Szadkowski, A. J.; Jakiela, R. et al.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Carrier localization in gallium nitride

Description: In wide bandgap GaN, a large number of interesting and important scientific questions remain to be answered. For example, the large free electron concentration reaching 10{sup 19} to 10{sup 20} cm{sup - 3} in nominally undoped material are ascribed to intrinsic defects because no chemical impurity has been found at such high concentrations. According to theoretical models, a nitrogen vacancy acts as a donor but its formation energy is very large in n-type materials, making this suggestion contr… more
Date: September 1, 1996
Creator: Wetzel, C.; Walukiewicz, W. & Haller, E.E.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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Layered manganites : magnetic structure at extreme doping levels.

Description: We report powder neutron diffraction results on the crystal and magnetic structures of the bilayer Ruddlesden-Popper phase Sr{sub 3}Mn{sub 2}O{sub 7{minus}{delta}} ({delta} = 0.0, 0.45) and correlate these structures with their magnetic and transport properties. The {delta} = 0.45 compound contains a large number of oxygen vacancies that are disordered in the MnO{sub 2} planes. As a result of this disordered vacancy structure, Sr{sub 3}Mn{sub 2}O{sub 6.55} is a nonmagnetic insulator. Sr{sub 3}M… more
Date: September 11, 1998
Creator: Mitchell, J. F.
Item Type: Refine your search to only Article
Partner: UNT Libraries Government Documents Department
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