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Origin of the pseudogap in high temperature superconductors

Description: Underdoped high temperature superconductors (HTS) exhibit a normal state for energies E > E{sub g} and/or temperatures T > T{sub 0}, and a pseudogap in their electronic spectrum for E < E{sub g} and/or T{sub 0} > T > {Tc}. Strikingly similar behavior occurs in the transition metal dichalcogenides (TMD) 2H-MX{sub 2}, where M = Ta, Nb, and X = S, Se, both in the normal (T > T{sub 0}) and in the incommensurate charge-density wave (T{sub ICDW} > T > T{sub c}) states. Such strikingly similar behavior has also been seen in the organic layered superconductors (OLS) {kappa}-(ET){sub 2}X, where ET is bis(ethylenedithio)tetrathiafulvalene, and X = Cu[N(CN){sub 2}]Br, and Cu(SCN){sub 2}, both in the normal region T > T{sub SDW} > {Tc} and in the spin-density wave region T{sub SDW} > T > T{sub c}. In all three materials classes, the anomalous transport and thermodynamic properties associated with the pseudogap or density-wave regime are completely independent of the applied magnetic field strength, whereas the same properties below {Tc} are all strongly field-dependent. Hence, the authors propose that the pseudogap in the HTS arises from charge- and/or spin-density waves, and not from either superconducting fluctuations or preformed charged quasiparticle pairs.
Date: February 8, 2000
Creator: Klemm, R. A.
Partner: UNT Libraries Government Documents Department

Formation of hollow nanocrystals through the nanoscale kirkendall effect

Description: We demonstrate that hollow nanocrystals can be synthesized through a mechanism analogous to the Kirkendall Effect, in which pores form due to the difference in diffusion rates between two components in a diffusion couple. Cobalt nanocrystals are chosen as a primary example to show that their reaction in solution with oxygen, sulfur or selenium leads to the formation of hollow nanocrystals of the resulting oxide and chalcogenides. This process provides a general route to the synthesis of hollow nanostructures of large numbers of compounds. A simple extension of this process yields platinum-cobalt oxide yolk-shell nanostructures which may serve as nanoscale reactors in catalytic applications.
Date: March 11, 2004
Creator: Yin, Yadong; Rioux, Robert M.; Erdonmez, Can K.; Hughes, Steven; Somorjai, Gabor A. & Alivisatos, A. Paul
Partner: UNT Libraries Government Documents Department

FY 2005 Miniature Spherical Retroreflectors Final Report

Description: Research done by the Infrared Photonics team at Pacific Northwest National Laboratory (PNNL) is focused on developing miniature spherical retroreflectors using the unique optical and material properties of chalcogenide glass to reduce both performance limiting spherical and chromatic aberrations. The optimized optical performance will provide efficient signal retroreflection that enables a broad range of remote detection scenarios for mid-wave infrared (MWIR) and long-wave infrared (LWIR) sensing applications. Miniature spherical retroreflectors can be developed to aid in the detection of signatures of nuclear proliferation or other chemical vapor or radiation signatures. Miniature spherical retroreflectors are not only well suited to traditional bistatic LIDAR methods for chemical plume detection and identification, but could enable remote detection of difficult semi-volatile chemical materials or low level radiation sources.
Date: December 1, 2005
Creator: Anheier, Norman C.; Bernacki, Bruce E.; Johnson, Bradley R.; Riley, Brian J. & Sliger, William A.
Partner: UNT Libraries Government Documents Department

Single Dirac Cone Topological Surface State and Unusual Thermoelectric Property of Compounds from a New Topological Insulator Family

Description: Angle resolved photoemission spectroscopy (ARPES) study on TlBiTe2 and TlBiSe2 from a Thallium-based III-V-VI2 ternary chalcogenides family revealed a single surface Dirac cone at the center of the Brillouin zone for both compounds. For TlBiSe{sub 2}, the large bulk gap ({approx} 200meV) makes it a topological insulator with better mechanical properties than the previous binary 3D topological insualtor family. For TlBiTe{sub 2}, the observed negative bulk gap indicates it as a semi-metal, rather than a narrow gap semi-conductor as conventionally believed; this semi-metality naturally explains its mysteriously small thermoelectric figure of merit comparing to other compounds in the family. Finally, the unique band structures of TlBiTe{sub 2} also suggests it as a candidate for topological superconductors.
Date: August 18, 2011
Creator: Chen, Y
Partner: UNT Libraries Government Documents Department

Summary of Chalcogenide Glass Processing: Wet-Etching and Photolithography

Description: This report describes a study designed to explore the different properties of two different chalcogenide materials, As2S3 and As24S38Se38, when subjected to photolithographic wet-etching techniques. Chalcogenide glasses are made by combining chalcogen elements S, Se, and Te with Group IV and/or V elements. The etchant was selected from the literature and was composed of sodium hydroxide, isopropyl alcohol, and deionized water and the types of chalcogenide glass for study were As2S3 and As24S38Se38. The main goals here were to obtain a single variable etch rate curve of etch depth per time versus NaOH overall solution concentration in M and to see the difference in etch rate between a given etchant when used on the different chalcogenide stoichiometries. Upon completion of these two goals, future studies will begin to explore creating complex, integrated photonic devices via these methods.
Date: December 1, 2006
Creator: Riley, Brian J.; Sundaram, S. K.; Johnson, Bradley R. & Saraf, Laxmikant V.
Partner: UNT Libraries Government Documents Department

Theory of Two-Magnon Raman Scattering in Iron Pnictides and Chalcogenides

Description: Although the parent iron-based pnictides and chalcogenides are itinerant antiferromagnets, the use of local moment picture to understand their magnetic properties is still widespread. We study magnetic Raman scattering from a local moment perspective for various quantum spin models proposed for this new class of superconductors. These models vary greatly in the level of magnetic frustration and show a vastly different two-magnon Raman response. Light scattering by two-magnon excitations thus provides a robust and independent measure of the underlying spin interactions. In accord with other recent experiments, our results indicate that the amount of magnetic frustration in these systems may be small.
Date: August 15, 2011
Creator: Chen, C. C.
Partner: UNT Libraries Government Documents Department

Final Project Report for ER15351 “A Study of New Actinide Zintl Ion Materials”

Description: The structural chemistry of actinide main-group metal materials provides the fundamental basis for the understanding of structural coordination chemistry and the formation of materials with desired or predicted structural features. The main-group metal building blocks, comprising sulfur-group, phosphorous-group, or silicon-group elements, have shown versatility in oxidation state, coordination, and bonding preferences. These building blocks have allowed us to elucidate a series of structures that are unique to the actinide elements, although we can find structural relationships to transition metal and 4f-element materials. In the past year, we investigated controlled metathesis and self-propagating reactions between actinide metal halides and alkali metal salts of main-group metal chalcogenides such as K-P-S salts. Ternary plutonium thiophosphates have resulted from these reactions at low temperature in sealed ampules. we have also focused efforts to examine reactions of Th, U, and Pu halide salts with other alkali metal salts such as Na-Ge-S and Na-Si-Se and copper chloride to identify if self-propagating reactions may be used as a viable reaction to prepare new actinide materials and we prepared a series of U and Th copper chalcogenide materials. Magnetic measurements continued to be a focus of actinide materials prepared in our laboratory. We also contributed to the XANES work at Los Alamos by preparing materials for study and for comparison with environmental samples.
Date: November 12, 2007
Creator: Dorhout, Peter K.
Partner: UNT Libraries Government Documents Department

Synthesis, characterization, and structure of reduced tungsten chalcogenide cluster complexes

Description: Over the previous twenty years, ternary molybdenum chalcogenides of the general formula M{sub x}Mo{sub 6}Y{sub 8} (M = ternary metal cation; Y = chalcogenide), known as Chevrel phases, have been extensively studied. Many of these compounds have been found to have superconductivity, catalytic activity and ionic conductivity. The rich chemistry of the Chevrel phases raises considerable interest in finding the tungsten analogues of these phases. However, no such analogue has ever been synthesized, although the Chevrel phases are usually prepared directly from elements at high temperatures above 1000{degrees}C. The absence of the tungsten analogues may be caused by their thermodynamic instability at such high temperatures. Thus it might be necessary to avoid high-temperature synthetic procedures in order to establish the ternary and binary tungsten chalcogenides. A major focus of the McCarley research group has been on the preparation of M{sub 6}Y{sub 8}L{sub 6} (M = Mo, W; Y = S, Se, Te) cluster complexes as low temperature pathways to the Chevrel phases.
Date: February 1, 1997
Creator: Xiaobing, Xie
Partner: UNT Libraries Government Documents Department

New class of diode-pumped, mid-IR, broadly-tunable lasers based on TM{sup 2+} lons in T{sub d} coordination: Cr{sup 2+}:ZnX (X=S,Se)

Description: A new class of room-temperature, diode-pumped solid state lasers, that are broadly tunable in the mid-infrared spectral region, has been conceptualized and demonstrated. These lasers are based on intra-ion transitions of divalent transition metals placed in substitutional cation sites of tetrahedral symmetry in large bandgap chalcogenide semiconductor crystals. These combinations of laser-ions and host crystals are seen to provide favorable radiative and non-radiative transition processes for the realization of the desired laser performance characteristics. Spectroscopic data for candidate schemes are reviewed and divalent chromium doped zinc chalcogenides are identified as potentially superior laser candidates. Preparation of laser quality Cr{sup 2+}:ZnSe crystals is described and experimental results to date for a diode-pumped laser are given. Remaining laser development issues are discussed briefly.
Date: January 1, 1997
Creator: Krupke, W.F.; Page, R.H.; Schaffers, K.I.; Payne, S.A.; Beach, R.J.; Skidmore, J.A. et al.
Partner: UNT Libraries Government Documents Department

Growth of thin film for waveguide laser: Development of chromium doped Zn chalcogenides as efficient, widely tunable mid-infrared lasers

Description: The incorporation of chromium in wide bandgap semiconductors is becoming a topic of interest in the development of efficient and compact tunable (range of 2--3 {micro}m) solid state mid-infrared lasers operating at room temperature. IN the search for optimized procedures of doping that will raise the chromium concentration to a level of 10{sup 20} ions/cm{sup 3}, the authors have developed a diffusion process in the temperature range of 750--950 C. However, optimization needs to be made during this process to preserve the optical transparency of the doped samples. The experimental data will be discussed in terms of dopant diffusivity, distribution of defects and crystal homogeneity.
Date: September 2, 1998
Creator: Burger, A. & Payne, S.A.
Partner: UNT Libraries Government Documents Department

Electrical and mechanical properties of oxide ceramics. Progress report, July 1978-April 1979

Description: Investigation is described for the electrical and mechanical properties of polycrystalline Al/sub 2/O/sub 3/, both doped and undoped, made from aluminum isopropoxide (so called Al/sub 2/O/sub 3/(II), as opposed to Al/sub 2/O/sub 3/(I) made from sulphate). The material is somewhat purer than Al/sub 2/O/sub 3/(I). Yet the undoped material, just as Al/sub 2/O/sub 3/(I), proved to be acceptor dominated. The electrical conductivity at high temperature (T>1300/sup 0/C) is similar to that of Al/sub 2/O/sub 3/(I), but at lower temperatures there is a contribution with a low activation energy. This contribution is independent of oxygen pressure and grain size and is largely ionic in nature.
Date: January 1, 1979
Creator: Kroeger, F. A.
Partner: UNT Libraries Government Documents Department

Effect of mechanical discontinuities on the strength of polycrystalline aluminum oxide

Description: This study examines the effect of artificially introduced spherical voids on the bend strength of a polycrystPalline brittle solid and compares the results to traditional empirical and phenomenological porosity-strength relationships. No correlation is found between these relationships and the data. The statistical approach by Weibull is examined particularly with regard to the implications to microstructural features. A direct test of Weibull statistics showed deviations from theory, perhaps due to the very small stressed volumes employed. Microstructural evidence suggests that some of the basic assumptions in Weibull's formulation may restrict its use in this and perhaps other systems. Based on the similarity between McClintock's statistical model and the observed microstructural features a failure criterion for systems with randomly distributed flaws is proposed. 25 references.
Date: September 1, 1978
Creator: Wallace, J.S.
Partner: UNT Libraries Government Documents Department

Sintering of polycrystalline ionic conductors:. beta. ''-Al/sub 2/O/sub 3/ and NASICON

Description: The densification kinetics for both ..beta..''-alumina and NASICON are dramatically different. ..beta..''-Alumina sinters by a reactive liquid process whereas NASICON densifies by a solid state method. More importantly, a qualitative examination of particle and agglomerate distributions, phase composition, linear shrinkage analysis, and heating rate effects can result in a concise determination of sintering processes without recourse to more quantitative techniques. Such a simple procedural method should be a basis for any beginning investigative study into the densification mechanism of new multicomponent ceramic materials.
Date: January 1, 1979
Creator: McEntire, B J; Miller, G R & Gordon, R S
Partner: UNT Libraries Government Documents Department

State of the art: alumina ceramics for energy applications

Description: Prominent ceramic raw materials and products manufacturers were surveyed to determine the state of the art for alumina ceramic fabrication. This survey emphasized current capabilities and limitations for fabrication of large, high-density, high-purity, complex shapes. Some directions are suggested for future needs and development.
Date: January 1, 1978
Creator: Hauth, W.E. & Stoddard, S.D.
Partner: UNT Libraries Government Documents Department

Application of controlled interfacial pore structures to kinetic studies in alumina

Description: The application of controlled-geometry interfacial pore structures to fundamental kinetic studies in alumina is described. Results from studies of the morphological stability of high aspect ratio pore channels, crack healing, pore coarsening and pore elimination in sapphire are presented.
Date: April 1, 1988
Creator: Roedel, J. & Glaeser, A.M.
Partner: UNT Libraries Government Documents Department

Study of plutonium oxide leak rates from shipping containers. Quarterly progress report, April 1, 1977--June 30, 1977

Description: The study was initiated in October, 1976. Several tasks are to be undertaken in the study. In combination, they have the end objective of defining the leak rates of plutonium oxide powder from characterized leaks. This is the third quarterly report of this work. Previous reports were issued as BNWL-2260-1 and -2. Progress on each of the tasks is reported. (TFD)
Date: July 1, 1977
Creator: Schwendiman, L.S.; Pobereskin, M.; Mishima, J.; Sutter, S.L.; Madia, W.J.; Schmidt, E.W. et al.
Partner: UNT Libraries Government Documents Department

Study of plutonium oxide leak rates from shipping containers. Quarterly progress report, October 1, 1977--December 31, 1977

Description: The study was initiated in Oct. 1976. Several tasks are to be undertaken. In combination, they have the end objective of defining the leak rates of plutonium oxide from characterized leaks in shipping containers. Research progress is reported on each of the four tasks. (TFD)
Date: January 1, 1978
Creator: Schwendiman, L.C.; Pobereskin, M.; Mishima, J.; Sutter, S.L.; Madia, W.J.; Schmidt, E.W. et al.
Partner: UNT Libraries Government Documents Department

Chemistry calculations relating to AIM

Description: This paper describes some single-cell rf-heating and air chemistry computations that are intended to model the conditions of an AIM experiment, either in a laboratory environment or in the atmosphere. For a pulsed mode of rf-induced ionization using repetitive 120-ns pulses with 1-ms separation we examine the relative amounts of power required to sustain ionization in the second and subsequent pulses compared to the first pulse. We also compare power requirements for sustained ionization at a pressure of 1 Torr (46 km altitude) and at 0.03 Torr (74 km altitude). The power needed in the 0.03-Torr case is substantially less than in the higher-pressure case. We find that at both pressures, using the rf power densities required to sustain ionization the neutral gas is heated very rapidly to temperatures exceeding 5000 K, leading to strong turbulence. We follow the chemical evolution of 55 species of atoms, molecules and ions, and we pay particular attention to the rate of production of N and NO, because of the effects of those species on the concentrations of stratospheric ozone. The N and NO production rates are not sufficient to cause serious concerns about ozone depletion. In the case representing 74 km altitude (P = 0.03 Torr) we find that quite high concentrations of NO will exist in the vicinity of the artificial ionization patch, leading to the possibility of enhanced local D-region ionization caused by the ionization of NO by solar Lyman-alpha. 30 figs.
Date: January 1, 1989
Creator: Zinn, J.; Sutherland, C.D. & Roussel-Dupre', R. (Los Alamos National Lab., NM (USA))
Partner: UNT Libraries Government Documents Department

Chemical flowsheet conditions for preparing urania spheres by internal gelation

Description: Small, ceramic urania spheres can be prepared for use as nuclear fuel by internal chemical gelation of uranyl nitrate solution droplets. Decomposition of hexamethylenetetramine (HMTA) dissolved in the uranyl nitrate solution releases ammonia to precipitate hydrated UO/sub 3/. Previously established flowsheet conditions have been improved and modified at ORNL and have been applied to prepare dense UO/sub 2/ spheres with average diameters of 1200, 300, and 30 ..mu..m.
Date: July 1, 1979
Creator: Haas, P.A.; Begovich, J.M.; Ryon, A.D. & Vavruska, J.S.
Partner: UNT Libraries Government Documents Department

Time dependence of average regional sulfur oxide concentrations

Description: The atmospheric burden of SO/sub 2/ and SO/sub 4/ in a large regional area has been calculated as a function of time during the July 1978 SURE intensive period. A formulism is developed in which a highly parameterized description of deposition and chemical conversion is combined with a realistic emissions inventory and with realistic trajectories as calculated with the BNL long-range air quality model, AIRSOX. Temporal variations in the regional atmospheric burden are calculated as being due to variations in the advection of material through the region, with the pollutant being advected having a characteristic half-life for its formation and decay. The calculated atmospheric burdens are divided by a nominal mixing height to derive an average ground-level concentration. Comparison is made with the corresponding concentrations derived from SURE observations. The regions for which these comparisons have been made are in the Midwest and East and are similar in size (approx. 5 x 10/sup 5/ KM/sup 2/) and location to areas commonly affected by regional sulfate episodes.
Date: March 1, 1980
Creator: Kleinman, L I; Carney, T A & Meyers, R E
Partner: UNT Libraries Government Documents Department