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Positron annihilation measurement of the vacancy formation enthalpy in copper. [25 to 1040/sup 0/C]

Description: Doppler-broadening and lifetime data obtained for Cu in the temperature region approx. 25 to 1040/sup 0/C are presented. The experiment utilized a new source-implantation technique. The value of the deduced vacancy formation enthalpy is 1.31 +- 0.05 eV. Since the Doppler-broadening data were the primary source for the determination of the vacancy formation enthalpy, the analysis of these data is discussed. The suitability of introducing divacancies into the analysis is also considered. It is concluded that the measured formation enthalpy is that for monovacancies.
Date: January 1, 1979
Creator: Fluss, M.J.; Smedskjaer, L.C.; Siegel, R.W.; Legnini, D.G. & Chason, M.K.
Partner: UNT Libraries Government Documents Department

Microstructures and phase transformations in interstitial alloys of tantalum

Description: The analysis of microstructures, phases, and possible ordering of interstitial solute atoms is fundamental to an understanding of the properties of metal-interstitial alloys in general. As evidenced by the controversies on phase transformations in the particular system tantalum--carbon, our understanding of this class of alloys is inferior to our knowledge of substitutional metal alloys. An experimental clarification of these controversies in tantalum was made. Using advanced techniques of electron microscopy and ultrahigh vacuum techology, an understanding of the microstructures and phase transformations in dilute interstitial tantalum--carbon alloys is developed. Through a number of control experiments, the role and sources of interstitial contamination in the alloy preparation (and under operating conditions) are revealed. It is demonstrated that all previously published work on the dilute interstitially ordered phase Ta/sub 64/C can be explained consistently in terms of ordering of the interstitial contaminants oxygen and hydrogen, leading to the formation of the phases Ta/sub 12/O and Ta/sub 2/H.
Date: January 1, 1979
Creator: Dahmen, U.
Partner: UNT Libraries Government Documents Department

Syntheses and structural characterization of zirconium-tin and zirconium-lead binary and ternary systems

Description: The binary zirconium-tin system was reinvestigated. The A15 phase appears to be a line phase with a Zr{sub 4}Sn composition. The Zr{sub 5}Sn{sub 3} (Mn{sub 5}Si{sub 3}-type) and Zr{sub 5}Sn{sub 4} (Ti{sub 5}Ga{sub 4}-type) compounds are line phases below 1000{degree}C, the latter being a self-interstitial phase of the former. ZrSn{sub 2} is the tin-richest phase. There is an one-phase region between these phases with partial self-interstitials at high temperatures. The zirconium-lead system behaves similarly: there are an A15 phase with a Zr{sub {approximately}5.8}Pb composition, Zr{sub 5}Pb{sub 3} (Mn{sub 5}Si{sub 3}-type) and Zr{sub 5}Pb{sub 4} (Ti{sub 5}Ga{sub 4-type}) compounds, and a high temperature solid solution between Zr{sub 5}Pb{sub >3.5} and Zr{sub 5}Pb{sub 4} from below 1000{degree}C; however, the ZrSn{sub 2} analogue is not formed. The Mn{sub 5}Si{sub 3}-type phases in these systems can accommodate third elements interstitially to form stoichiometric compounds Zr{sub 5}Sn{sub 3}Z (Z = B, C, N, O, Al, Si, P, S, Cu, Zn, Ga, Ge, and As and Se) and Zr{sub 5}Pb{sub 3}Z (Z = Al, Si, P, S, Fe, Co, Ni, Cu, Zn, Ga, Ge, As, Se, Ag, Cd, In, Sn, Sb and Te) as well as their self-interstitial derivatives. The systems Zr-Sn-T, T = Fe, Co and Ni, did not produce stoichiometric interstitial phases Zr{sub 5}Sn{sub 3}T. Instead, the interstitial phases for these elements are formed only with excess tin that partially occupies the interstitial site together with a T element. Reducing the amount of tin in these systems yields two new phases; Zr{sub 5}Sn{sub 2+x}Fe{sub 1-x} (0 {le} {times} {le} 0.28) (W{sub 5}Si{sub 3}-type) and Zr{sub 6}Sn{sub 2}Fe (Zr{sub 6}Al{sub 2}Co-type) as characterized by X-ray single crystal analyses. A cobalt analogue for the latter was also synthesized.
Date: January 28, 1991
Creator: Kwon, Y.U.
Partner: UNT Libraries Government Documents Department

Electro- and thermotransport of carbon in iron-nickel alloys

Description: Results of studies on the electrotransport, thermotransport and chemical diffusion of carbon in ..gamma..-phase iron - 32.5 wt % nickel alloys are described. The transport parameters, Z, Q and D were measured as a fucntion of temperature and carbon concentration and values for the activation energies for diffusion and electrotransport were obtained. The solubility limit of carbon in ..gamma..-Fe-32.5 wt % Ni for the temperature range 850 to 1200/sup 0/C and the electrical resistivity versus temperature for carbon concentrations of 0.0, 0.1, 0.2, 0.5 and 0.86 wt % C between 25 and 1350/sup 0/C were determined. An anomalously large mass transport effect observed in two-phase alloy during thermotransport experiments was investigated for the Fe-Ni-C system.
Date: March 1, 1980
Creator: Okafor, I.C.I.
Partner: UNT Libraries Government Documents Department

Frank loop formation in irradiated metals in response to applied and internal stresses

Description: The Frank loop and dislocation microstructures developed in three face-centered cubic alloys during fast reactor irradiation have been examined to determine the influence of applied and internally-generated stress on loop evolution. It is shown that anisotropic stresses generate a corresponding anisotropy of Frank loop populations on the four close-packed planes. The loop populations thus represent a microstructural record of the irradiation creep processes in action. The ease of interpreting this record depends on the relative magnitudes of external and internal stresses. Metals with low irradiation creep rates which also undergo concurrent and substantial phase changes during irradiation are subject to large and indeterminate levels of internally-generated stress which render the microstructural record uninterpretable with respect to the applied stress state. When the internally-generated stresses are small in comparison to the externally-applied stresses, a clear record of the SIPA (Stress-Induced-Preferential-Absorption) growth mechanism of irradiation creep is imprinted at low neutron fluences in the density and sizes of loops present on each set of close-packed planes. This record fades at higher fluences when the continued anisotropic formation, growth and unfaulting of Frank loops generates a corresponding anisotropy in the resultant free dislocation network, a process which alters the competition of sinks for point defects.
Date: April 1, 1980
Creator: Gelles, D.S.; Garner, F.A. & Brager, H.R.
Partner: UNT Libraries Government Documents Department

Frank loop unfaulting mechanism in fcc metals during neutron irradiation

Description: The unfaulting mechanism whereby sessile Frank dislocation loops evolve into a complex tangle of glissile dislocations during irradiation of face centered cubic metals is not well understood. It is presumed that such loops grow by absorption of point defects until interactions develop which provide sufficient impetus for nucleation of an unfaulting event. The loops then become glissile, interact and form a dislocation network. An alternate mechanism which has been observed to occur in an austenitic precipitation-strengthened commercial alloy irradiated in the EBR-II fast reactor. The mechanism requires an interaction between the sessile a/3 <111> Frank loop and a moving glissile a/2 <110> perfect dislocation. An unfaulting a/6 <112> dislocation is created which, as it moves, eliminates the Frank loop and leaves only a perfect dislocation with the original a/2 <110> Burgers vector. This process is demonstrated. This alternate mechanism can have significant impact on the development of the dislocation microstructure in a metal undergoing irradiation creep. This impact will be discussed in relation to relevant irradiation creep models.
Date: May 1, 1980
Creator: Gelles, D.S.
Partner: UNT Libraries Government Documents Department

Ordered structures in YBa/sub 2/Cu/sub 3/O/sub 7-y/, La/sub 2-x/Sr/sub x/CuO/sub 4-par. delta/ and related perovskites

Description: Electron microscopy and electron diffraction studies have been performed on the superconducting oxides YBa/sub 2/Cu/sub 3/O/sub 7-y/, GdBa/sub 2/Cu/sub 3/O/sub 7-y/ and La/sub 2-x/Sr/sub x/CuO/sub 4-par. delta/ as well as the related perovskites La/sub 2/CuO/sub 4/, Eu/sub 2/CuO/sub 4/ and Gd/sub 2/CuO/sub 4/. Extra reflections are commonly observed in all the cases. For example, in the 123 compounds, in situ heating leads to transformations from orthorhombic to tetragonal with a loss of twin structure; on cooling the oxygen vacancies re-order in the basal plane to give 1/3(100)* or 1/4(110)* diffraction spots. In tetragonal Eu/sub 2/CuO/sub 4/ and Gd/sub 2/CuO/sub 4/, the (001) diffraction patterns often have extra spots at 1/2(110)* or at 1/4(110)* positions. Extra spots are also observed in La/sub 2/CuO/sub 4/ (orthorhombic) but this is probably due to the space group being primitive rather than centered. These observations are discussed in terms of the ordering of oxygen vacancies in the Cu-O planes of the various perovskite structures. 6 figs.
Date: January 1, 1988
Creator: Mitchell, T.E.; Roy, T.; Fisk, Z. & Smith, J.L.
Partner: UNT Libraries Government Documents Department

Diffusion of hydrogen and its isotopes in BCC metals

Description: It has been suggested that light interstitials in metals diffuse in much the same manner as do self-trapped electronic carriers (small polarons) in semiconductors and insulators. The motion is assumed to occur via a succession of phonon-assisted quantum-mechanical tunneling events. Such interstitial jumps were modeled formally by adopting Holstein's non-adiabatic approach to small-polaron hopping motion. It is the purpose of the present work to transcend this theory and explicitly calculate the diffusion constant for models of the interatomic interactions associated with an interstitial in a metal. With this procedure the conditions under which quantum-mechanical tunneling is the predominant mode of light interstitial transport in metals was investigated. In situations characterized by inerstitial tunneling motion the validity of simplifying assumptions of the formal theory were examined. It was found that there are meaningful examples of light interstitial diffusion which do not correspond to tunneling through a barrier. In those instances where tunneling motion does prevail, the influence of excited states of the interstitial wells, the breakdown of the Condon approximation, and the predominance of adiabatic hopping qualitatively affect the hopping rate. The occurrence of these situations reflects fundamental physical differences between an electron tunneling between the relatively deep potential wells of an insulator and an atom moving between interstitial positions in a metal. The magnitudes, temperature dependences and isotope dependences of the calculated diffusion constants are consistent with existing diffusion data on bcc metals.
Date: January 1, 1979
Creator: Emin, D.; Baskes, M.I. & Wilson, W.D.
Partner: UNT Libraries Government Documents Department

Diffuse x-ray scattering studies of n and e/sup -/-irradiated Ni and dilute Ni alloys

Description: Pure Ni and dilute NiSi and NiGe alloys were irradiated at 6 K with either fast neutrons or 3 MeV electrons. The resulting defect structures were studied using diffuse x-ray scattering methods after different annealing treatments. For both types of irradiation of pure Ni, large interstitial and vacancy dislocation loops developed on annealing. In contrast, interstitial agglomerates in a NiSi/sub .01/ alloy contained no more than approx. =10 interstitials, and few vacancy loops were observed. Complete recovery was observed at lower temperatures in the alloy. Similar results were found for NiGe/sub .01/, although larger interstitial clusters were observed. The results are discussed within the model for the trapping reactions developed previously to explain the results of e/sup -/ irradiation of these same alloys.
Date: August 1, 1986
Creator: Averback, R.S. & Ehrhart, P.
Partner: UNT Libraries Government Documents Department

Radiation effects and micromechanics of SiC/SiC composites

Description: The basic displacement damage process in SiC has been fully explored, and the mechanisms identified. Major modifications have been made to the theory of damage dosimetry in Fusion, Fission and Ion Simulation studies of Sic. For the first time, calculations of displacements per atoms in SiC can be made in any irradiation environment. Applications to irradiations in fusion first wall neutron spectra (ARIES and PROMETHEUS) as well as in fission spectra (HIFIR and FFTF) are given. Nucleation of helium-filled cavities in SiC was studied, using concepts of stability theory to determine the size of the critical nucleus under continuous generation of helium and displacement damage. It is predicted that a bimodal distribution of cavity sizes is likely to occur in heavily irradiated SiC. A study of the chemical compatibility of SiC composite structures with fusion reactor coolants at high-temperatures was undertaken. It was shown that SiC itself is chemically very stable in helium coolants in the temperature range 500--1000[degree]C. However, current fiber/matrix interfaces, such as C and BN are not. The fracture mechanics of high-temperature matrix cracks with bridging fibers is now in progress. A fundamentally unique approach to study the propagation and interaction of cracks in a composite was initiated. The main focus of our research during the following period will be : (1) Theory and experiments for the micro-mechanics of high-temperature failure; and (2) Analysis of radiation damage and microstructure evolution.
Date: January 1, 1992
Creator: Ghoniem, N.M.
Partner: UNT Libraries Government Documents Department

Annealing behavior and selected applications of ion-implanted alloys

Description: Thermally activated processes cause ion-implanted metals to evolve from the initial state toward thermodynamic equilibrium. The degree of equilibration is strongly dependent upon temperature and is considered for three temperature regimes which are distinguished by the varying mobilities of interstitial and substitutional atoms. In addition, perturbations resulting from the irradiation environment are discussed. Examples are given of the use of implanted and annealed alloys in studies of diffusion, phase diagrams, and solute trapping.
Date: June 1, 1978
Creator: Myers, S.M.
Partner: UNT Libraries Government Documents Department

Solid state, surface and catalytic properties of oxides. Progress report, October 1, 1979-October 31, 1980

Description: Fundamental studies on oxide catalysts have been conducted with emphasis on the investigation of the properties of anion and cation vacancies on an oxide surface, on the characterization of an adsorbed oxygen species on an oxide, and on the determination of surface cation densities in solid oxide solutions. An automically well ordered surface of ZnO has been successfully prepared on which a high density of sites resembling those of the anion vacancy is present. Such a surface adsorbs oxygen and methanol more strongly, yet carbon dioxide more weakly than a stoichiometric nonpolar surface. From the kinetics of adsorption and desorption, evidence of an atomic adsorption of oxygen on iron oxide has been observed. The adsorption of this species is activated, and its desorption follows a bimolecular rate law. Attempts are being made to obtain the activation energies of adsorption and desorption, and the saturation coverage of the species. Its reaction with hydrocarbons will be studied later. The surface cation densities of Fe and Cr on a series of solid solutions of Fe/sub 2/O/sub 3/-Cr/sub 2/O/sub 3/ were determined. It was found that Fe was enriched on the surface at low Fe contents, but depleted from the surface at high Fe contents. The surface Cr on air treated samples is Cr(VI). Calculation on the surface cation densities of oxide solid solutions of cubic structure was performed using a pairwise potential, and a statistical model for the surface layer. For dilute bulk solutions, the larger cation is found to be enriched on the surface.
Date: October 1, 1980
Creator: Kung, H.H.
Partner: UNT Libraries Government Documents Department

Positron lifetime measurements as a non-destructive technique to monitor fatigue damage. Final report, January 1, 1971--June 30, 1978. [Electrons, vacancies]

Description: Positron studies were applied successfully to cyclic fatigue in steel and copper and have shown a capability to nondestructively detect fatigue softening and fatigue hardening. In the case of elastic high cycle fatigue in initially soft steel the fatigue hardening is identified with point defects. For cyclic plastic range, high cycle fatigue cyclic hardening and softening are correlated with changes in dislocation substructure. Positron measurements during the pulse annealing of copper single crystals following electron irradiation at 77/sup 0/K have revealed the formation of multi-vacancy complexes which constitute the precursors of radiation induced voids. Positron studies have been applied to hydrogen embrittlement in 4340 steel and more recently in nickel. The technique can non-destructively detect hydrogen embrittlement and gage its extent. U.S. Patent No. 4064438 was issued on this basis.
Date: June 1, 1978
Creator: Byrne, J.G.
Partner: UNT Libraries Government Documents Department

Multiple sectioning and perforation techniques for TEM sub-surface studies. [4 MeV Ni/sup +2/ ions]

Description: Techniques for preparing multiple electron transparent regions at several depth levels below the surface of a metal disk specimen are described. These techniques are relatively rapid and find application in many areas involving surface studies. Examples are shown of multiple thin areas produced at intervals of approximately 200 nm below the original surface of a stainless steel bombarded with 4 MeV Ni/sup +2/ ions for void swelling studies.
Date: January 1, 1978
Creator: Lee, E.H. & Rowcliffe, A.F.
Partner: UNT Libraries Government Documents Department

Oxygen diffusion in hypostoichiometric uranium dioxide

Description: The tracer oxygen diffusivity in UO/sub 2-x/ has been measured along the lower two phase boundary. The diffusion couple consisted of two matched hypostoichiometric uranium dioxide wafers, one enriched with /sup 18/O and the other normal. Results showed much higher diffusion coefficients than those of stoichiometric UO/sub 2/. This directly proved that the major defect species in UO/sub 2-x/ is the anion vacancy. Activation energy of anion vacancy migration was measured to be 11.7 +- 3.0 kcal/mole. A diffusion model established for UO/sub 2/ and UO/sub 2+-x/ showed that in stoichiometric UO/sub 2/ both interstitials and vacancies contribute significantly to oxygen diffusion and neither can be neglected; at 1400/sup 0/C their contributions are about equal. This model was extended to nearly stoichiometric UO/sub 2+-x/ to predict oxygen diffusion coefficients in these stoichiometry ranges. Also deduced from the model were the Frenkel defect energy and entropy of 85.6 +- 9.2 kcal/mole and 18.2 +- 7.3 eu, respectively. The contribution of Frenkel disorder to the excess enthalpy of UO/sub 2/ was evaluated. Calculation showed that Frenkel disorder accounts for 87% of the excess enthalpy at 3000/sup 0/K. A simple two band model for electronic excitation, with a band gap of 2.0 ev and effective electron mass of 7.6 m/sub e/, accounted for the remainder of the excess enthalpy.
Date: December 1, 1980
Creator: Kim, K.C.
Partner: UNT Libraries Government Documents Department

High-temperature Moessbauer study of /sup 57/Fe interstitials in Chevrel phases

Description: Moessbauer measurements have been made at /sup 57/Fe nuclei in the Chevrel phase compound Fe/sub 0/ /sub 05/SnMo/sub 6/S/sub 8/ from 300 to 1100K and Fe/sub 0/ /sub 05/HoMo/sub 6/S/sub 8/ from 80 to 673K. Iron atoms are found to be in two electronic states which are attributed to Fe monomers and dimers in Cu-II-like crystallographic sites. No evidence of diffusive broadening is observed to 1100K for Fe atoms in the Fe/sub 05/SnMo/sub 6/S/sub 8/ compound. The iron atoms are apparently in deep interstitial traps bound to S and Sn atoms. Thermal cycling experiments indicate that phase decomposition is occurring at temperatures of about 400C for the Ho compound and 800C for the Sn compound.
Date: January 1, 1980
Creator: Stafford, B.L.; Karlov, T.F.; Kimball, C.W. & Fradin, F.Y.
Partner: UNT Libraries Government Documents Department

Study of the anisotropy of the threshold energy in copper using in-situ electrical resistivity measurements in the HVEM

Description: In the past, electrical-resistivity measurements and high voltage electron microscopy-(HVEM) have been used separately to investigate the anisotropy of the threshold energy for Frenkel-pair production. Electrical resistivity, measured in a conventional electron accelerator, has been used to observe small changes in the concentration of isolated Frenekel pairs at low temperatures, while HVEM experiments have focussed on the observation of measurable changes in visible defect clusters, primarily at elevated temperatures. However, quantitative comparison of the threshold energies obtained with the two techniques has proved difficult. As a first step toward resolving this dilemma, the threshold-energy surface for copper was determined by in-situ electrical-resistivity measurements below 10 K in the HVEM. By combining the advantages of both techniques, this approach allowed a precise and detailed study of the anisotropy of the threshold energy for Frenkel-pair production.
Date: January 1, 1980
Creator: King, W.E.; Merkle, K.L. & Meshii, M.
Partner: UNT Libraries Government Documents Department

Electronic structure studies of YBa[sub 2]Cu[sub 3]O[sub x](6. 2 [le] x [le] 6. 9) using angle resolved photoemission

Description: Using high resolution angle resolved photoemission, the electronic structure of YBa[sub 2]Cu[sub 3]O[sub x] is examined when oxygen stoichiometries are varied in the range 6.2 [le] [times] [le] 6.9. Detailed measurements of the Fermi surface for YBa[sub 2]Cu[sub 3]O[sub 6.9] are presented and are compared with predictions of band theory. In the metallic region of the phase diagram, changes in the Fermi surfaces are measured as a function of oxygen stoichiometry. The electronic structure is monitored as the oxide changes from a metal to a semiconductor with additional oxygen depletion. For intermediate stoichiometries, effects of oxygen vacancy ordering are considered. Unusual resonant effects observed at several photon energies are examined as oxygen content is varied.
Date: November 1, 1992
Creator: Veal, B.W.; Liu, Rong; Paulikas, A.P.; Koelling, D.D.; Downey, J.W. (Argonne National Lab., IL (United States)); Shi, Hao (Argonne National Lab., IL (United States) Missouri Univ., Kansas City, MO (United States). Dept. of Physics) et al.
Partner: UNT Libraries Government Documents Department

Self-diffusion of Er and Hf inpure and HfO/sub 2/-doped polycrystalline Er/sub 2/O/sub 3/. [Hf-175 and Er-169]

Description: Using a tracer technique, self-diffusion of Er and Hf was measured over the approximate temperature interval of 1600 to 1970/sup 0/C in pure and HfO/sub 2/-doped polycryatalline Er/sub 2/O/sub 3/. Up to about 10 m/o HfO/sub 2/ dopant level, the Er self-diffusion coefficients followed a relationship based on cation vacancies. Above 10 m/o HfO/sub 2/, deviation from this relationship occurred, apparently due to clustering of cation vacancies and oxygen interstitials around the dopant hafnia ion. The activation energy for the self-diffusion of Er in pure Er/sub 2/O/sub 3/ was 82.2 Kcal/mole and increased with the HfO/sub 2/ dopant level present. Self-diffusion of Hf was measured in pure Er/sub 2/O/sub 3/ having two impurity levels, and a separation of the grain boundary. The volume diffusion of Hf showed both extrinsic and intrinsic behavior with the transition temperature increasing with the impurity level present in Er/sub 2/O/sub 3/. The activation energy for Hf volume diffusion in the intrinsic region was high, i.e. 235 -+ 9.5 Kcal/mole. The grain boundary diffusion was apparently extrinsic over the entire temperature interval Very low Hf self diffusion rates were found in both pure and HfO/sub 2/ doped Er/sub 2/O/sub 3/ compositions. Despite a clustering effect, the HfO/sub 2/ dopant increased the Hf volume diffusion coefficients.
Date: January 1, 1979
Creator: Scheidecker, R.W.
Partner: UNT Libraries Government Documents Department

Positron annihilation in solid and liquid Ni

Description: New techniques have been developed for the study of metals via positron annihilation which provide for the in-situ melting of the samples and subsequent measurements via Doppler broadening of positron-annihilation radiation. Here we report these metods currently in use at our laboratory; ion implantation of /sup 58/Co and the use of Al/sub 2/O/sub 3/ crucibles for in-situ melting followed by the decomposition of the Doppler-broadened spectrum into a parabolic and a Gaussian component. Our earliest results obtained for pure Ni in the polycrystalline solid and in the liquid state are compared. An interesting similarity is reported for the distributions of the high-momentum (Gaussian) component for positrons annihilating in vacancies at high temperatures and those annihilating in liquid Ni.
Date: March 1, 1982
Creator: Fluss, M.J.; Smedskjaer, L.C.; Chakraborty, B. & Chason, M.K.
Partner: UNT Libraries Government Documents Department

Photoluminescence and structural characterization of MeV erbium implanted silica glass

Description: Suprasil glass (amorphous SiO{sub 2}) has been implanted with 2.9 MeV Er ions at fluences of 3.4 {times} 10{sup 15} and 3.4 {times} 10{sup 16} ions/cm{sup 2}. Photoluminescence spectra of implanted samples show a clear luminescent transition around {lambda} = 1.54 {mu}m, corresponding to an intra-4f transition of Er{sup 3+}. Fluorescence decay times are in the range 1--8 ms., depending on implantation fluence and annealing treatment. UV absorption and IR reflection spectroscopy are employed to characterize beam-induced defects in the silica network. The results indicate that defects in the silica network play an important role in the energy transfer processes in the Er:silica system. 15 refs., 3 figs.
Date: January 1, 1990
Creator: Polman, A.; Jacobson, D.C.; Lidgard, A.; Poate, J.M. (AT and T Bell Labs., Murray Hill, NJ (USA)) & Arnold, G.W. (Sandia National Labs., Albuquerque, NM (USA))
Partner: UNT Libraries Government Documents Department

Diffusion studies in amorphous NiZr alloys

Description: Tracer impurity and self diffusion measurements have been made on amorphous (a-) NiZr alloys using radioactive tracer, Secondary Ion Mass Spectrometry and Rutherford backscattering techniques. The temperature dependence of diffusion in a-NiZr can be represented in the form D = D/sub 0/exp(-Q/kT), with no structural relaxation effects being observed. The mobility of an atom in a-NiZr increased dramatically with decreasing atomic radius of the diffusing atom and also with decreasing Ni content for Ni concentrations below approx. =40 at. %. These diffusion characteristics in a-NiZr are remarkably similar to those in ..cap alpha..-Zr and ..cap alpha..-Ti. These mechanisms assume that Zr and Ti provide a close packed structure, either crystalline or amorphous, through which small atoms diffuse by an interstitial mechanism and large atoms diffuse by a vacancy mechanism. 12 refs., 2 figs., 2 tabs.
Date: June 1, 1987
Creator: Hahn, H.; Averback, R.S.; Hoshino, K. & Rothman, S.J.
Partner: UNT Libraries Government Documents Department

PAC spectroscopy of electronic ceramics

Description: Dilute indium dopants in cerium oxides and YBa{sub 2}Cu{sub 3}O{sub x} have been studied by{sup 111}In/Cd Perturbed Angular Correlation (PAC) spectroscopy. By controlling oxygen vacancy concentration in the cerium oxides through doping or high-temperature vacuum annealing, we have found that indium always forms a defect complex unless the sample is doped to reduce greatly the oxygen vacancy concentration. Three different vacancy-associated complexes are found with concentrations that depend on doping and oxygen stoichiometry. Another defect complex occurs in samples having negligible vacancy concentration. At low temperatures, evidence is found of interaction with an electronic hole trapped by {sup 111}Cd after the radioactive decay of the {sup 111}In parent. In YBa{sub 2}Cu{sub 3}O{sub x} the indium substitutes preferentially at the Y site but has measurable probability of substitution in at least one of the two copper sites. A symmetry change near 650 {degree}C is consistent with the well-documented orthorhombic/tetragonal transition for samples in air or oxygen.
Date: January 1, 1991
Creator: Gardner, J.A.; Wang, Ruiping; Schwenker, R. (Oregon Univ., Eugene, OR (United States). Dept. of Physics); Evenson, W.E. (Brigham Young Univ., Provo, UT (United States). Dept. of Physics and Astronomy); Rasera, R.L. (Maryland Univ., Catonsville, MD (United States). Dept. of Physics) & Sommers, J.A. (Teledyne-Wah Chang, Albany, OR (United States))
Partner: UNT Libraries Government Documents Department