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The concept of quasi-particles forms the theoretical basis of our microscopic understanding of emergent phenomena associated with quantum mechanical many-body interactions. However, quasi-particle theory in disordered materials has proven difficult, resulting in the predominance of mean-field solutions. Here we report first-principles phonon calculations and inelastic x-ray and neutron scattering measurements on equiatomic alloys (NiCo, NiFe, AgPd, and NiFeCo) with force constant dominant disorder - confronting a key 50-year-old assumption in the Hamiltonian of all mean-field quasi-particle solutions for off-diagonal disorder. Our results have revealed the presence of a large, and heretofore unrecognized, impact of local chemical environments on the distribution of the species-pair-resolved force constant disorder that can dominate phonon scattering. This discovery not only identifies a critical analysis issue that has broad implications for other elementary excitations such as magnons and skyrmions in magnetic alloys, but also provides an important tool for the design of materials with ultra-low thermal conductivity., Comment: 25 pages, 6 figures

This investigation experimentally determines the as-irradiated crystal axes dimensional change of the common polytypes of SiC considered for nuclear application. Single crystal α-SiC (6H), β-SiC (3C), CVD β-SiC, and single crystal Si have been neutron irradiated near 60 °C from 2 × 1023 to 2 × 1026 n/m2 (E > 0.1 MeV), or about 0.02–20 dpa, in order to study the effect of irradiation on bulk swelling and strain along independent crystalline axes. Single crystal, powder diffractometry and density measurement have been carried out. For all neutron doses where the samples remained crystalline all SiC materials demonstrated equivalent swelling behavior. Moreover the 6H–SiC expanded isotropically. The magnitude of the swelling followed a ∼0.77 power law against dose consistent with a microstructure evolution driven by single interstitial (carbon) mobility. Extraordinarily large ∼7.8% volume expansion in SiC was observed prior to amorphization. Above ∼0.9 × 1025 n/m2 (E > 0.1 MeV) all SiC materials became amorphous with an identical swelling: a 11.7% volume expansion, lowering the density to 2.84 g/cm3. The as-amorphized density was the same at the 2 × 1025 and 2 × 1026 n/m2 (E > 0.1 MeV) dose levels.

The nature of defect clusters in Ni and Ni 50 Co 50 (NiCo) irradiated at room temperature with 2–16 MeV Ni ions is studied using asymptotic diffuse X-ray scattering and transmission electron microscopy (TEM). Analysis of the scattering data provides separate size distributions for vacancy and interstitial type defect clusters, showing that both types of defect clusters have smaller sizes and higher densities in NiCo than in Ni. Diffuse scattering results show good quantitative agreement with TEM size distributions for cluster sizes greater than 2 nm in diameter, but we find that TEM under represents the number of defect clusters ≤ 2 nm, which comprise the majority of vacancy clusters in NiCo. Interstitial dislocation loops and stacking fault tetrahedra are identified by TEM. Comparison of diffuse scattering lineshapes to those calculated for dislocation loops and SFTs indicates that most of the vacancy clusters are SFTs.

X-ray microcomputed tomography (μCT) was applied in characterizing the internal structures of a number of irradiated materials, including carbon-carbon fibre composites, nuclear-grade graphite and tristructural isotropic-coated fuel particles. Local cracks in carbon-carbon fibre composites associated with their synthesis process were observed with μCT without any destructive sample preparation. Pore analysis of graphite samples was performed quantitatively, and qualitative analysis of pore distribution was accomplished. It was also shown that high-resolution μCT can be used to probe internal layer defects of tristructural isotropic-coated fuel particles to elucidate the resulting high release of radioisotopes. Layer defects of sizes ranging from 1 to 5 μm and up could be isolated by tomography. As an added advantage, μCT could also be used to identify regions with high densities of radioisotopes to determine the proper plane and orientation of particle mounting for further analytical characterization, such as materialographic sectioning followed by optical and electron microscopy. In fully ceramic matrix fuel forms, despite the highly absorbing matrix, characterization of tristructural isotropic-coated particles embedded in a silicon carbide matrix was accomplished using μCT and related advanced image analysis techniques.

Phase competition underlies many remarkable and technologically important phenomena in transition metal oxides. Vanadium dioxide (VO2) exhibits a first-order metal-insulator transition (MIT) near room temperature, where conductivity is suppressed and the lattice changes from tetragonal to monoclinic on cooling. Ongoing attempts to explain this coupled structural and electronic transition begin with two alternative starting points: a Peierls MIT driven by instabilities in electron-lattice dynamics and a Mott MIT where strong electron-electron correlations drive charge localization. A key missing piece of the VO2 puzzle is the role of lattice vibrations. Moreover, a comprehensive thermodynamic treatment must integrate both entropic and energetic aspects of the transition. Here we report that the entropy driving the MIT in VO2 is dominated by strongly anharmonic phonons rather than electronic contributions, and provide a direct determination of phonon dispersions. Our ab initio calculations identify softer bonding in the tetragonal phase, relative to the monoclinic phase, as the origin of the large vibrational entropy stabilizing the metallic rutile phase. They further reveal how a balance between higher entropy in the metal and orbital-driven lower energy in the insulator fully describes the thermodynamic forces controlling the MIT. Our study illustrates the critical role of anharmonic lattice dynamics in metal oxide phase competition, and provides guidance for the predictive design of new materials.

The development of ultra-brilliant synchrotron X-ray sources enables characterization methods that are particularly important for nuclear materials. Here we discuss emerging synchrotron methods with unprecedented signal-to-noise, spatial and time resolution. Microprobe methods are discussed that extend virtually any X-ray characterization measurement to ultra-small sample volumes. This ability is critical to resolve heterogeneities in nuclear materials and for studies on volumes with vastly lower activity than are needed for traditional X-ray characterization. Specific methods discussed include microdiffraction for the characterization of local crystal structure and micro-spectroscopy techniques that allow for characterization of elemental distributions with sensitivity for daughter products, oxidation states and diffusion through buffer layers. Opportunities are also discussed that exploit the high brilliance and pulsed nature of synchrotron radiation to reduce backgrounds from sample radiation and to study materials dynamics.

The austenitisation (α→γ) transformation in a 1005 C–Mn steel is monitored in real time at continuous heating rates between 1 and 10°C s−1 using in situ synchrotron X-ray diffraction and validated using dilatometry. Experimental validation is provided for austenitisation models that predict that the austenitisation transformation proceeds through multiple mechanisms. At temperatures below the A1 transformation temperature, the starting microstructure undergoes recovery and recrystallisation to relieve stress imparted during the initial thermomechanical processing of the steel. The austenitisation transformation follows, beginning at the A1 temperature, with the initial transformation proceeding as the pearlite in the microstructure is dissolved and high carbon concentration austenite is formed. Since the carbon is localised near the original pearlite colonies, there is a pronounced heating rate dependent delay before the remaining low C ferrite grains begin to transform. The transformation reaches...

Ag nanoink sintering kinetics and subsequent melting is studied using in situ synchrotron-based X-ray diffraction. Direct observations of Ag nanoink sintering on Cu demonstrate its potential for materials joining since the Ag nanoink sinters at low temperatures but melts at high-temperatures. Results show low expansion coefficient of sintered Ag, nonlinear expansion as Ag densifies and interdiffuses with Cu above 500 °C, remelting consistent with bulk Ag, and eutectic reaction with Cu. The results demonstrate the usefulness of Ag nanoink as a high-temperature bonding medium.

The pyrochlore Lanthanum Zirconium Oxide, La2Zr2O7 (LZO), has been developed as a potential replacement barrier layer in the standard RABiTS three-layer architecture of physical vapor deposited CeO2 cap/YSZ barrier/Y2O3 seed on Ni–5%W metal tape. The main focus of this research is to ascertain whether: (i) we can further improve the barrier properties of LZO; (ii) we can modify the LZO cation ratio and still achieve a high level of performance; and (iii) it is possible to reduce the number of buffer layers. We report a systematic investigation of the LZO film growth with varying compositions of La:Zr ratio in the La2O3–ZrO2 system. Using a metal–organic deposition (MOD) process, we have grown smooth, crack-free, epitaxial thin films of LaxZr1−xOy (x = 0.2–0.6) on standard Y2O3 buffered Ni–5W substrates in short lengths. Detailed XRD studies indicate that a single epitaxial LZO phase with only (0 0 1) texture can be achieved in a broad compositional range of x = 0.2–0.6 in LaxZr1−xOy. Both CeO2 cap layers and MOD–YBCO films were grown epitaxially on these modified LZO barriers. High critical currents per unit width, Ic of 274–292 A/cm at 77 K and self-field were achieved for MOD–YBCO films grown on LaxZr1−xOy (x = 0.4–0.6) films. These results indicate that LZO films can be grown with a broad compositional range and still support high performance YBCO coated conductors. In addition, epitaxial MOD LaxZr1−xOy (x = 0.25) films were grown directly on biaxially textured Ni–3W substrates. About 3 μm thick YBCO films grown on a single MOD–LZO buffered Ni–3W substrates using pulsed laser deposition show a critical current density, Jc, of 0.55 MA/cm2 (Ic of 169 A/cm) at 77 K and 0.01 T. This work holds promise for a route for producing simplified buffer architecture for RABiTS based YBCO coated conductors.

Difficult nucleation of β-Sn during solidification of tin and tin-based lead-free solder alloys can result in high degrees of undercooling of the liquid prior to solidification. The undercooling can produce solder joints with large grains, anisotropic behavior, and undesirable mechanical properties. This paper describes our examination of the amount of undercooling of tin on both graphite (non-wetting) and copper (wetting) surfaces using in situ x-ray diffraction. The microstructure was further characterized by optical microscopy, scanning electron microscopy, and electron backscattering diffraction imaging microscopy. Undercoolings as high as 61°C were observed for Sn solidified on graphite, while lower undercoolings, up to 30°C, were observed for Sn solidified on copper. The microstructure of the high purity Sn sample solidified on graphite showed very few grains in the cross-section, while the commercially pure Sn sample solidified with only one grain and was twinned. Tin solidified on copper contained significant amounts of copper in the tin, intermetallic phase formation at the interface, and a eutectic microstructure.

Single-crystal diffuse X-ray microdiffraction was used to characterize radiation-induced defects in individual grains of a polycrystalline proton-irradiated Fe foil., Single-crystal diffuse X-ray scattering was used to characterize radiation-induced defects in individual grains of a polycrystalline proton-irradiated Fe foil. The grains were probed with an intense 1 µm X-ray beam to demonstrate that both polycrystalline and micrometer-scale samples can be studied with single-crystal-like signal-to-noise. Scattering was measured with an X-ray-sensitive area detector, which measures intensity over a surface in reciprocal space. By scanning the X-ray energy, the intensity was measured over reciprocal-space volumes. Since the sample is not rotated, the real-space scattering volume does not change. Methods to minimize experimental artifacts arising from the use of an area detector are described.

The effect of alloying elements on the mechanical properties and weldability of wrought gamma prime strengthened nickel based superalloys is well known. An understanding of the basic guidelines concerning alloying additions has led to the invention and development of HAYNES 282 alloy for applications in aircraft and land based gas turbines and other high performance high temperature environments. The alloy combines exceptional high temperature properties with good weldability and fabricability. At high temperatures (∼900°>C), the alloy is stronger in creep strength than Waspaloy alloy (UNS N07001) and it approaches the creep strength of R-41 alloy (UNS N07041). Because the alloy has better thermal stability, fabricability and weldability than Waspaloy and R-41 alloys, it is currently being considered as a candidate universal consumable for welding/repair welding of gamma prime strengthened nickel based superalloys and it is also being considered as a suitable replacement for applications where R-4...

We have developed a simplified buffer layer architecture for the rolling-assisted biaxially textured substrates (RABiTS) template approach. The overall purpose of this research is to enable potentially a low-cost, high throughput and high yield manufacturing processes for buffer fabrication and to gain fundamental understanding of the growth of buffer layers for RABiTS templates. This understanding is critical to the development of a reliable, robust, and long-length manufacturing process for second generation wires. In this study, efforts are being made to either reduce the number of vacuum deposited layers or to replace one or more of these vacuum deposited layers with a solution based layer. We have chosen Gd2O3 - ZrO2 system as a potential barrier layer for this study. We have deposited epitaxial Gadolinia Stabilized Zirconia (GSZ) (Zr1-xGdxOy; x = 0-1) films on 30-nm thick e-beam evaporated Y2O3 seeded Ni-W (3 at. %) (Ni-3W) substrates using a metal-organic decomposition (MOD) process. Detailed X-ray studies indicated that all of the MOD-GSZ layers were cube textured and both in-plane and out-of-plane lattice parameters increases linearly with increasing the Gd content. We have also developed process conditions for reactively sputter deposited epitaxial Gd2Zr2O7 (Gadolinium Zirconium Oxide (GZO); Zr1-xGdxOy (x = 0.5)) films on the e-beam evaporated Y2O3/Ni - 3W substrates. YBCO films with a critical current density Jc of 2.14 times 106 A / cm2 and 1.4 times 106 A / cm2 at 77 K and self-field were grown on the newly developed architectures of Gd2Zr2O7/Y2O3/Ni - 3W and Zr1-xGdxOy (x = 0.2)/Y2O3/Ni - 3W substrates, respectively using a pulsed laser deposition (PLD) process. This work promises a route for producing cost-effective simplified buffer architectures for the RABiTS-based YBCO coated conductors.

Synchrotron radiation was used to directly observe the transformation of ferrite, austenite and sigma phases during heating and cooling of 2205 duplex stainless steel. Sigma formed during the initial stages of heating, dissolved as the temperature was increased, and reformed on cooling. The dissolution temperature of sigma was measured to be 985 ± 2.8 °C at a heating rate of 0.25 °C/s, and the kinetics of sigma formation at 850 °C was determined to be slower after dissolving at 1000 °C than before.

Two different types of defect structures have been identified to be responsible for the enhanced pinning in metal organic deposited YBCO films. Rare earth additions result in the formation of nanodots in the YBCO matrix, which form uncorrelated pinning centers, increasing pinning in all magnetic field orientations. 124-type intergrowths, which form as laminar structures parallel to the ab-plane, are responsible for the large current enhancement when the magnetic field is oriented in the ab-plane. TEM studies showed that the intergrowths emanate from cuprous containing secondary phase particles, whose density is partially controlled by the rare earth doping level. Critical process parameters have been identified to control this phase formation, and therefore, control the f 24 intergrowth formation. This work has shown that through process control and proper conductor design, either by adjusting the composition or by multiple coatings of different functional layers, the desired angular dependence can be achieved.

The formation and growth of sigma (σ) phase in 2205 duplex stainless steel (DSS) was observed and measured in real time using synchrotron radiation during 10 hour isothermal heat treatments at temperatures between 700 °C and 850 °C. Sigma formed in near-equilibrium quantities during the isothermal holds, starting from a microstructure which contained a balanced mixture of metastable ferrite and austenite. In-situ synchrotron diffraction continuously monitored the transformation, and these results were compared to those predicted by thermodynamic calculations. The data were further analyzed using a modified Johnson–Mehl–Avrami–Kolmogrov (JMAK) approach to determine kinetic parameters for sigma formation over this temperature range. The initial JMAK exponent, n, at low fractions of sigma was found to be approximately 7.0; however, toward the end of the transformation, n decreased to values of approximately 0.75. The change in the JMAK exponent was attributed to a change in the transformation mechanism from discontinuous precipitation with increasing nucleation rate, to growth of the existing sigma phase after nucleation site saturation occurred. Because of this change in mechanism, it was not possible to determine reliable values for the activation energy and pre-exponential terms for the JMAK equation. While cooling back to room temperature, the partial transformation of austenite resulted in a substantial increase in the ferrite content, but sigma retained its high-temperature value to room temperature.

Yttria stabilized zirconia (YSZ) is one of the inert matrix candidates selected for investigation as host matrix for minor actinide (MA) transmutation. The structural properties of (Zr0.84, Y0.16)O1.92 beads prepared by a sol–gel method for MA infiltration, are characterized as calcined (850 °C) and sintered (1,600 °C) beads. The calcined YSZ beads are fine-grained and homogenous over the entire sphere and are surrounded by a uniform outer layer of approximately 30 μm thickness. After sintering at 1,600 °C, the beads are compacted to 51% of their initial volume and exhibit a granular structure. The thermal expansion is nearly linear for the calcined material, but shows a parabolic behavior for the sintered (1,400 °C) beads. In addition, the thermal expansion of calcined material is 20–25% less than after sintering. During heating up to 1,400 °C, two processes can be distinguished. The first occurs between 900 and 1,000 °C and is related to an increase in unit cell order. The second process involves grain-growth of the less crystalline calcined material between 1,100 and 1,300 °C. These results have implications for preparation of YSZ and its use as an inert MA transmutation matix.

In situ x-ray diffraction was performed while annealing thin film Au∕Cu binary diffusion couples to directly observe diffusion at elevated temperatures. The temperature dependence of the interdiffusion coefficient was determined from isothermal measurements at 700, 800, and 900°C, where Cu and Au form a disordered continuous face centered cubic solid solution. Large differences in the lattice parameters of Au and Cu allowed the initial diffraction peaks to be easily identified, and later tracked as they merged into one diffraction peak with increased diffusion time. Initial diffusion kinetics were studied by measuring the time required for the Cu to diffuse through the Au thin film of known thickness. The activation energy for interdiffusion was measured to be 65.4kJ∕mole during this initial stage, which is approximately 0.4× that for bulk diffusion and 0.8× that for grain boundary diffusion. The low activation energy is attributed to the high density of columnar grain boundaries combined with other defec...

The effects of the as-cast microstructure on the oxidation characteristics of two Ni-Al-Cr alloys with either γ or γ′ primary solidification were investigated with an in-situ, time-resolved X-ray diffraction (TRXRD) technique using synchrotron radiation. The measurements, carried out during rapid heating and cooling, showed that a segregated microstructure in these cast alloys leads to the preferential formation of zirconium oxide before the formation of aluminum oxides is detected. The oxidation leads to a change in the phase stability and to the modification of surface microstructures. Computational thermodynamic models were used to explain the preferential formation of oxides in the as-cast microstructure.

The isothermal transformation of high-carbon austenite-to-bainitic ferrite has been investigated with the in-situ technique of time-resolved X-ray diffraction using synchrotron radiation. The measurements indicate that prior to transformation, the austenite divided into regions with significantly different lattice parameters. It is possible that this is due to the development of carbon-rich and carbon-poor regions in the austenite, as a precursor to transformations including the bainite reaction. The lattice parameter became uniform as transformation progressed and the fraction of carbon-poor austenite decreased. The ferrite itself exhibited a large range of lattice parameters during the early stages of transformation, due to the trapping of carbon.

Nanocrystalline Cr–Fe–Ni thin films libraries are prepared by radio frequency magnetron sputter codeposition on Al 2 O 3 substrates. The variation in distance from different points on the substrate to the three sputter sources produces a spread in composition in the films. Synchrotron radiation is used to analyze composition, crystallographic phase, and grain size as a function of sample position, both as- deposited and after annealing. In addition to three equilibrium phases (bcc, fcc and σ-FeCr), a fourth phase is observed which does not correspond to any equilibrium phase in the Cr–Fe–Ni system, but which is consistent with the α-Mn structure. The films are initially nanocrystalline; both equilibrium and nonequilibrium phases are observed. Ternary phase diagrams measured at annealing temperatures of 200–800 °C show that the stability of nanocrystalline material against thermal grain growth varies widely with composition, and that the crystallographic phase can be selected to be an appropriate heat treatment. Thus, the approach used here is useful for technologies such as magnetic recording media where understanding the stability of the nanograin structure is critical.

Characterization tests were made of a commercial carburization treatment that has shown promise for hardening the surfaces of the austenitic stainless steel target vessel of the Spallation Neutron Source against cavitation erosion and pitting caused by the action of pulsed pressure waves in the liquid mercury target. The findings support most of the provider’s promotional claims. The high surface hardness and the thickness of the hardened layer are validated, as are the hardness-depth profiles. The austenite lattice of the layer is enlarged and placed in a state of compressive stress and the surface is plastically distorted by the treatment. The corrosion resistance of the surface in selected acid media is greater than that for untreated austenite. The treated surface is not brittle and is quite resistant to cracking during straining. The maximum carbon content of the layer is measured at 3–4.5 wt%, versus 6–7 wt% cited by the provider. Contrary to the provider’s assertion that all of the carbon is contained in supersaturated solid solution in the austenite phase, some of the carbon is present in an iron carbide phase located non-uniformly at the very surface. Inclusion stringers and δ-ferrite phase in the carburized layer are more prone to corrosion and may provide preferential sites for cavitation pitting.

Isothermal tests were performed on Ti–6Al–4V to observe time-dependent changes in the lattice parameter of the α (hexagonal close-packed) and β (body-centered cubic) phases. Synchrotron-based experiments show contraction in β at temperatures below 550 °C, and expansion at higher temperatures. Contraction results from annealing of preexisting residual stresses, while expansion results from V diffusion when the α → β phase transformation becomes kinetically active.

YBa2Cu3Oy (YBCO) films produced by the ex situ conversion of BaF2-based precursors deposited by physical vapor deposition on ion-beam assisted deposited (IBAD) yttrium-stabilized zirconia (YSZ) and rolling-assisted biaxially textured substrates (RABiTS) templates are characterized by a bi-axially aligned, laminar grain structure that results from the anisotropic growth characteristics of the YBCO phase and its precipitation from a transient liquid phase during the conversion process. A bimodal microstructure characterizes these films and is defined by large, well-formed YBCO grains with Y2O3 precipitates in the bottom region of the film and small YBCO grains with a high density of stacking faults in the upper half. Ba2Cu3Oy or Ba–O–F/CuO second phase layers were often found between large YBCO grains in the bottom half of the films. YBCO grain sizes exceeded 50 μm within the plane of the film in some cases. Conversely, discrete secondary phases of Y2Cu2O5, Y2O3, and Ba2Cu3Oy/Ba–O–F could be found among the much smaller YBCO grains in the top portion of the bimodal structure. The dividing line of the bimodal structure was generally at one half of the film thickness, although exceptions to this trend were found. The highest critical current densities (Jc) and best film alignments for a given film thickness were found in samples where the layers of Ba2Cu3Oy or Ba–O–F were minimized or eliminated from the films. Samples quenched after partial conversion show the segregation of CuO to the top region of the film and the lateral growth of large YBCO grains from a precursor mix of Y2Cu2O5 and Ba–O–F. The data demonstrate that transient liquid phases are part of the conversion process of BaF2-based YBCO films. The control of both CuO segregation and the amount of liquid phases generated during the initial stages of phase formation is needed for optimizing the ex situ conversion process for high-Jc coated conductors.

In situ X-ray diffraction experiments using synchrotron radiation were performed on Ti–6Al–4V samples to directly observe the α → β phase transformation during heating. These experiments were conducted at the Advanced Photon Source (APS) using a 30 keV synchrotron X-ray beam to monitor changes in the α and β phases as a function of heating time under different heating rates. The results were compared to computational thermodynamic predictions of the phase fractions versus temperature, providing information about the kinetics of the α → β transformation in Ti–6Al–4V. The measured transformation rates were shown to be consistent with a diffusion-controlled growth mechanism, whereby diffusion of V in the β-Ti phase controls the rate. Based on the X-ray diffraction data, real time measurements of the α and β phase lattice parameters were made. Dramatic differences were observed in the changes of the lattice parameters of the two phases during the transformation. These changes are believed to be due to the partitioning of V and its strong effect on the lattice parameter of the β phase. An unexpected contraction of the lattice parameter of the β phase was further observed during heating in the temperature range between 500 and 600 °C. The origin of this contraction is most likely related to the annealing of residual stresses created by the different thermal expansion behaviors of the two phases.

Several techniques have been investigated for making alloy libraries for combinatorial materials development. In this investigation, we demonstrate a method for Ni–Fe–Cr ternary alloy library preparation by deposition of three layers of different metals with a linear thickness gradient rotated by 120° for each layer. The layers were interdiffused and alloyed by annealing in vacuum. The resulting specimens were analyzed and compared with the well-known phase diagram for this system by means of rapid x-ray diffraction mapping with synchrotron radiation.

A technique based on synchrotron radiation was developed that allows for rapid structural and chemical characterization of ternary alloys over a wide range of composition. The technique was applied to isothermal sections of the Cr–Fe–Ni system grown on Al2O3(0001) sapphire substrates by sequential deposition of layers of graded.thickness followed by annealing to interdiffuse the elements. A film spanning the Cr–Fe–Ni ternary system was measured in 4 h at a resolution of 2 at.% by rastering the sample under a focused beam of synchrotron radiation while simultaneously measuring the diffraction pattern with a charge-coupled device detector to determine crystallographic phases, texture, and lattice parameters and also measuring the x-ray fluorescence with an energy-dispersive detector to determine elemental composition. Maps of phase composition and lattice parameter as a function of composition for several annealing treatments were found to be consistent with equilibrium values. The technique will be useful in combinatorial materials design.

In situ X-ray diffraction has been used to study the conversion of ∼3000 A thick, evaporated barium fluoride precursor films to YBCO on buffered metal substrates for a range of conversion time, ramp rate, water vapor pressure, oxygen pressure, and temperature. All films were taken from the same continuously processed tape. Critical current densities as high as 1.34 MA/cm 2 have been obtained for a precursor reaction rate of 2.0 A/s. Higher reaction rates (up to 17 A/s) lead to lower critical current densities and incompletely developed YBCO. The reaction rate increases with increasing P H 2 O , increasing T , and decreasing P O 2 . The reaction rate increases linearly with increasing P H 2 O for the range of pressures used here (0.0125–5.0 mTorr). The formation of non-epitaxial YBCO is generally associated with lower T and higher reaction rate, whereas the formation of barium cerate, which results from a reaction of the precursor and the CeO 2 -capped substrate, is generally associated with higher T and lower reaction rate. General trends in the formation of crystalline phases during conversion may serve as a baseline for development of higher rate conversion processing for thicker, higher performance YBCO.

Focused monochromatic synchrotron undulator radiation was used to measure stresses in growing α-Al2O3 on FeCrAl-based and NiAl alloys during the first few hours of high-temperature air exposures at 1000–1200°C. Selected specimens were then sectioned and examined by transmission electron microscopy to characterize the microstructure of the oxides grown during the in situ stress measurement experiments. In several cases at 1100 and 1200°C, rapid decreases in an initial tensile stress were noted within the first hour of exposure. It was found that differences in high-temperature stress development in the alumina were at least partially reflected in the observed scale microstructures. Relaxation processes limited the magnitude of growth stresses at the higher temperatures such that after a few hours, stresses were typically quite low.

Fabrication of a biaxially textured, strengthened Ni substrate with small alloying additions of W and Fe is reported. The substrates have significantly improved mechanical properties compared to 99.99% Ni and surface characteristics which are similar to that of 99.99% Ni substrates. High quality oxide buffer layers can be deposited on these substrates without the need for any additional surface modification steps. Grain boundary misorientation distributions obtained from the substrate show a predominant fraction of low-angle grain boundaries. A high critical current density, J c , of 1.9 MA/cm 2 at 77 K, self-field is demonstrated on this substrate using a multilayer configuration of YBCO/CeO 2 /YSZ/Y 2 O 3 / Ni–3at.%W–1.7at.%Fe. This translates to a I c /width of 59 A/cm at 77 K and self-field. J c at 0.5 T is reduced by only 21% indicating strongly-linked grain boundaries in the YBCO film on this substrate.

Solution-based techniques have been examined as potential low-cost processes for manufacturing YBCO coated conductors. YBCO films prepared from metal trifluoroacetate precursors have achieved performance levels equaling or exceeding that of vapor deposited films with the same thickness on CeO/sub 2//YSZ(sc) substrates. J/sub c/'s of 4.5 MA/cm/sup 2/ and 2 MA/cm/sup 2/ have been achieved in 0.4 /spl mu/m thick YBCO films on CeO/sub 2//YSZ(sc) and CeO/sub 2//YSZ/CeO/sub 2//Ni substrates, respectively. Textured Gd/sub 2/O/sub 3/ buffer layers have been deposited on deformation textured Ni substrates in a reel-to-reel process. The performance of YBCO films deposited on substrates containing the Gd/sub 2/O/sub 3/ seed layers is comparable in performance to YBCO films grown on all vacuum deposited buffer layers.

Chemical solution epitaxy was used to deposit an epitaxial film of Gd2O3 on roll-textured nickel. A 2-methoxyethanol solution of gadolinium methoxyethoxide was used for spin-coating and dip-coating. Films were crystallized using a heat treatment at 1160 °C for 1 h in 4% H2/96% Ar. Single-layer films were approximately 600 Å in thickness, and thicker films could be produced using multiple coatings. θ/2θ x-ray diffractograms revealed only (0041) reflections, indicating a high degree of out-of-plane texture. A pole-figure about the Gd2O3 (222) reflection indicated a single in-plane epitaxy. Scanning electron microscopy showed that the films were smooth, continuous, and free of pin holes. Atomic force microscopy revealed an average surface roughness of 53 Å. Electron diffraction indicated that the misalignment of the majority of the grains in the plane was less than 10°. High-current (0.4 MA/cm2) Yba2Cu3O7–δ films were grown on roll-textured nickel substrates using Gd2O3 as the base layer in a three-layer buffer structure.

Methoxyethoxide complexes in 2-methoxyethanol were used to produce epitaxial thin films of SrBi2Nb2O9, SrBi2Ta2O9, BaBi2Nb2O9, and BaBi2Ta2O9 on [100] oriented single-crystals of SrTiO3 and LaAlO3. Films were prepared by spin coating substrates with alkoxide solutions and firing in air at 850 °C for 20 minutes. With the exception of BaBi2Ta2O9 on LaAlO3, all of the films were the desired c-axis oriented Aurivillius phase. Out-of-plane orientation was confirmed by θ-2θ scans which showed only [002/] reflections, and in-plane orientation was determined by phi-scans about the [105] plane. Lattice constants and full-width at half-maximum (fwhm) values for both in-plane and out-of-plane reflections are reported.

In order for many large-scale bulk applications of high-temperature superconducting materials to be realized, the cost/performance of the superconductors needs to be optimized. From a performance standpoint, a long, flexible, single-crystal-like wire is required; from a cost-and-fabrication standpoint, an industrially scalable, low-cost process is required. Both of these critical requirements are met by rolling-assisted biaxially textured substrates, a conductor-fabrication technique that employs simple, scalable, thermomechanical processing techniques to obtain a near-single-crystal-like, flexible metal substrate in arbitrary lengths on which epitaxial oxide buffer layers and superconductors are then deposited.

Much of the conductor development effort in the last decade has focused on optimizing the processing of (Bi, Pb)2Sr2Ca2Cu3Ox oxide-powder-in-tube conductors and (Bi, Pb)2Sr2CaCu2O8 (Bi-2212) and TlBa2Ca2Cu3Ox thick film conductors. It is demonstrated that in each of these conductors, critical current densities are dictated by the grain boundary misorientation distributions (GBMD's). Percolative networks of low-angle boundaries with fractions consistent with the active cross-sectional area of the conductor exist in each of these conductors. Further enhancements in the properties require increased numbers of small-angle grain boundaries. Given the processing methods used to fabricate these materials, no clear route employing a simple modification of the established processing method is apparent. To address this need, conductors with controlled or predetermined GBMD's are necessary. Development of biaxial texture appears to be the only possible way to increase the number of small-angle boundaries in a practical and controllable manner. We summarize in this paper recent results obtained on epitaxial superconducting films on rolling-assisted-biaxially-textured-substrates (RABiTS). This technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield structurally and chemically compatible surfaces. Epitaxial YBa2Cu3O7–δ films grown using laser ablation on such substrates have critical current densities exceeding 106 A/cm2 at 77 K in zero field and have a field dependence similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of the next generation high temperature superconducting (HTS) wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

A LaAlO3 precursor solution was prepared via an all alkoxide sol-gel route. The solution of lanthanum methoxyethoxide and aluminum methoxyethoxide in 2-methoxyethanol was prepared via ligand exchange starting from lanthanum isopropoxide and aluminum sec-butoxide and was used to make both LaAlO3 powders and films. Complete hydrolysis of the solution formed a gel that yielded well-crystallized LaAlO3 powders when fired in air at 800 °C. A partially hydrolyzed solution was spun-cast on SrTiO3 (100) single crystal substrates. Epitaxial films of LaAlO3 were subsequently formed during pyrolysis in O2 at 800 °C in a rapid thermal annealing furnace for a total of 8 min. The films were strongly c-axis oriented, verified by x-ray rocking curve results from the (003) plane with full-width at half-maximum (FWHM) = 0.87°, and had good in-plane texture shown by a φ scan of the (202) plane with FWHM = 1.07°.

We report on the superconducting properties of TlBa2Ca2Cu3O9−y (Tl-1223) thick films grown on smooth and rough Ag substrates. Thallium-free precursor films of the type Ba2Ca2Cu3Ag0.37O7 were deposited on Ag substrates using a spray-pyrolysis technique followed by post-thallination in a two-zone furnace. X-ray diffraction (XRD) results showed the presence of c-axis aligned Tl-1223 films and some degree of local in-plane texture (often referred to as a colony microstructure). The microstructure of the Ag surface dictates the growth behavior of Tl-1223 films. The transport critical-current densities (Jc) for Tl-1223 films grown on smooth and rough Ag substrates were ∼ 65,000 A/cm2 and ˜ 37,000 A/cm2, respectively, at 77 K and zero field. The films grown on smooth Ag substrates were strongly linked and had good in-field properties with a Jc value of ∼104 A/cm2 at 77 K and 0.5 T.

The electron backscattering pattern technique has been applied to the microstructural investigation of Tl(1223) thick films formed by vapor-phase thallination of Ag-containing Ba–Ca–Cu–oxide precursors. For samples grown on polycrystalline YSZ, considerable biaxial alignment is found in localized, multigrain regions as wide a 100 μm or more. However, on scales above 1 mm the overall texture remains only uniaxial with the c-axes (i.e., [001]) aligned perpendicular to the plane of the substrate. On single-crystal KTaO3 an epitaxial relationship is evident which persists to the surface of a 3 μm thick film. Modest variations in the processing protocol yield films containing grains oriented with the c-axis in the plane, resulting in the degradation of transport properties. The data suggest a growth mode in which sparse nucleation occurs at the substrate followed by rapid lateral crystallization.

Fabrication of Tl-1223 conductors in two geometries is reported. Powder-in-tube (PIT) tapes were fabricated using aerosol generated precursor powders mixed with Tl/sub 2/O/sub 3/. Effect of processing variables such as temperature, time and uniaxial pressure were studied. Under optimum processing conditions the tapes have sharp transitions (widths /spl sim/1 K) and zero-field J/sub c//spl sim/0.9/spl times/10/sup 4/ A/cm/sup 2/ at 77 K, However the tapes lack any detectable grain orientation texture and are severely weak-linked. On the other hand, thick films (3-30 /spl mu/m) of Tl-1223 on Ag made using a variety of precursor deposition techniques followed by thallination in a two-zone flow reactor, show significantly reduced weak-link behavior and high zero-field J/sub c/'s (>10/sup 4/ A/cm/sup 2/). It is found that these films are c-axis aligned (rocking curve FWHM/spl sim/3-11/spl deg/) and also possess varying degrees of local in-plane texture. Microstructural development in these thick films is found to be similar to that observed previously for films on polycrystalline YSZ. Such thick films present a working model of a practical Tl-1223 conductor. >

In the course of investigating synthesis routes, stability information was developed for YBa2Cu3O7−x, Y2Ba4Cu7O15−x, and YBa2Cu4O8. The results were obtained between ∼900 and 1040 °C and involve oxygen pressures between 10 and 145 atm. The observations show that the PO2‐T ranges for stability of the three phases overlap and that some stable mixtures of the phases can be synthesized. The results are compared to the results of other experimental studies and to calculations based on calorimetric data.

At low oxygen potentials, YBa2Cu3O7−x decomposes by chemical reactions involving reduction. The results of this study show that the compound also decomposes at higher oxygen potentials. The initial decomposition products were found to be Y2BaCuO5 and a Ba‐Cu oxide phase. The Ba‐Cu phase was found to be a peroxide‐type and the decomposition can be described by a chemical reaction involving oxidation: 4(YBa2Cu3O7−x)+(1/2 − 3/2δ +2x)O2⇄2Y2BaCuO5+3Ba2Cu3O6−δ+CuO. At 800 °C the equilibrium pressure for this reaction is slightly

We have used x-ray diffraction to characterize diamond films grown in three characteristic morphologies by chemical vapor deposition. Each morphology has a fiber texture about the growth direction; we report the crystal axis aligned in this direction for each morphology. In all cases the average lattice constant agrees with that of bulk diamond; we report the range of strain in each sample.

In-plane—aligned, c axis—oriented YBa2Cu3O7 (YBCO) films with superconducting critical current densities Jc as high as 700,000 amperes per square centimeter at 77 kelvin have been grown on thermomechanically rolled-textured nickel (001) tapes by pulsed-laser deposition. Epitaxial growth of oxide buffer layers directly on biaxially textured nickel, formed by recrystallization of cold-rolled pure nickel, made possible the growth of YBCO films 1.5 micrometers thick with superconducting properties that are comparable to those observed for epitaxial films on single-crystal oxide substrates. This result represents a viable approach for the production of long superconducting tapes for high-current, high-field applications at 77 kelvin.

A method to obtain long lengths of flexible, biaxially oriented substrates with smooth, chemically compatible surfaces for epitaxial growth of high‐temperature superconductors is reported. The technique uses well established, industrially scalable, thermomechanical processes to impart a strong biaxial texture to a base metal. This is followed by vapor deposition of epitaxial buffer layers (metal and/or ceramic) to yield chemically compatible surfaces. Epitaxial YBa2Cu3Ox films grown on such substrates have critical current densities exceeding 105 A/cm2 at 77 K in zero field and have field dependencies similar to epitaxial films on single crystal ceramic substrates. Deposited conductors made using this technique offer a potential route for the fabrication of long lengths of high‐Jc wire capable of carrying high currents in high magnetic fields and at elevated temperatures.

A possible microstructural origin of the high critical current densities which have been obtained in c‐axis‐aligned, polycrystalline TlBa2Ca2Cu3O8+x deposits has been identified. The results of x‐ray diffraction determinations of basal plane texture of Tl‐1223 deposits prepared by spray pyrolysis are observed to depend on the size of the x‐ray beam. Furthermore, most grain boundaries were found from transmission electron microscopy to have small misorientation angles. It is concluded that although overall the basal plane orientations are nearly random, there is a high degree of local texture indicative of colonies of similarly oriented grains. The spread in a‐axis orientation within a colony is ∼10°–15°. Intercolony conduction, it is suggested, may be enhanced by a percolative network of small‐angle grain boundaries at colony interfaces.

The four real values of the dielectric function tensor of the monoclinic crystal Lu2SiO5 or lutetium oxyorthosilicate (LSO) have been determined using generalized ellipsometry from 200 to 850 nm. The three principal values are fit to the Sellmeier model and they indicate that the band gap of LSO is less than ∼9 eV. The off-diagonal element e12 is non-zero over the entire spectrum, but it is very close to zero for wavelengths longer than ∼400 nm, indicating that structurally monoclinic LSO is nearly optically orthorhombic in this wavelength region. The spectroscopic dielectric functions of three isotropic ceramic LSO samples are presented, which are consistent with the dielectric functions of single-crystal LSO when the effects of optical density are included. As a comparison, the dielectric functions are also determined using relativistic electronic structure and optical calculations based on the recently developed potential functional of Tran and Blaha [Phys. Rev. Lett. 102, 226401 (2009)].

This study reports on the fabrication of metal-organic chemical vapor deposited (MOCVD) YBa2Cu3O6+δ (YBCO) films doped with varying amounts of Ce and Ho and the characterization of their electrical, microstructural, and chemical properties. The films are prepared by vapor phase deposition of a Y-Ba-Cu precursor mix containing controlled amounts of Ce and Ho onto buffered metal strip templates. The comprehensive characterization of these films by critical current measurement, transmission electron microscopy, x-ray diffraction, Raman microspectroscopy, and x-ray absorption spectroscopy provides detailed information about the structure/chemistry/performance relationships and how they vary with varying amounts of Ce and Ho in the YBCO films. The microstructure exhibited by both the Ce-doped and the Ho-doped films contains a high density of crystal basal-plane aligned, fluoritelike precipitates within the YBCO matrix. For optimally doped samples, the influence of these nanocrystalline phases on the flux pinni...

A unique, three-dimensional (3D), biaxially textured, MgO, nanofence comprised of single crystal MgO nanobelt segments or links was synthesized via epitaxial growth on (100) SrTiO(3) substrates. Individual single crystal MgO nanobelt segments comprising the nanofence have a square cross-section with dimensions in the range of 10-20 nm and with lengths in the range from 100 nm up to 1 microm. X-ray diffraction shows that the 3D MgO nanofence has an epitaxial relation with (100) SrTiO(3) substrates with a cube-on-cube, {100}100 orientation and with values of the full width at half-maximum of the (200) omega-scan and the (110) varphi-scan at 4.5 degrees and 5.5 degrees , respectively. Such a biaxially textured oxide nanofence with single crystal segments can be used as a 3D nanotemplated substrate for epitaxial growth of wide-ranging, 3D, electronic, magnetic and electromagnetic nanodevices.

The focus of the present research is to develop an integrated deformation and recrystallization model for magnesium alloys at the microstructural length scale. It is known that in magnesium alloys nucleation of recrystallized grains occurs at various microstructural inhomogeneities such as twins and localized deformation bands. However, models need to be developed that can predict the evolution of the grain structure and texture developed during recrystallization and grain growth, especially when the deformation process follows a complicated deformation path such as in asymmetric rolling. The deformation model is based on a crystal plasticity approach implemented at the length scale of the microstructure that includes deformation mechanisms based on dislocation slip and twinning. The recrystallization simulation is based on a Monte Carlo technique that operates on the output of the deformation simulations. The nucleation criterion during recrystallization is based on the local stored energy, and the Monte Carlo technique is used to simulate the growth of the nuclei resulting from local stored energy differences and curvature. The model predictions are compared with experimental data obtained through electron backscatter analysis and neutron diffraction.

In-situ X-ray diffraction (XRD) measurements using high energy synchrotron radiation were performed to monitor in real time the formation of delta ferrite in a martensitic 9 wt pct chromium steel under simulated weld thermal cycles. Volume fractions of martensite, austenite, and delta ferrite were measured as a function of temperature at a 10 K/s heating rate to 1573 K (1300 °C) and subsequent cooling. At the peak temperature, the delta ferrite concentration rose to 19 pct, of which 17 pct transformed back to austenite on subsequent cooling., Max Kade Foundation, Inc., Austrian Academy of Sciences, United States. Dept. of Energy (Division of Materials Sciences and Engineering, Office of Science, and Office of Basic Energy Sciences)