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An understanding of heteroepitaxy between perovskite and alkaline earth oxides is developed in terms of ion size and interfacial electrostatics. Interfacial energy minimization at the first atomic layers is the basis for a commensurate, unit-cell stability. This unit-cell stability presents the opportunity to study reduced dimensional or two-dimensional phenomena in thin-film ferroelectrics and is the basis for growth of high crystal quality, \ensuremath{\mu}m-thick films for optical device applications.

Iron aluminides with the composition Fe-45Al-5X-0.2B-0.1Zr (at. %), where X stands for the first row transition metals Ti, V, Cr, Mn, Fe, Co, Ni, Cu, were examined at room temperature with respect to their strength, ductility, environmental sensitivity, and fracture mode. The extruded materials were annealed at 1273 K to produce similar grain sizes and subsequently at 673 K to reduce the amount of quenched in vacancies. All alloys were essentially single phase. Their solid solution strengthening was found to correlate with the atomic size misfit derived from the lattice parameters. The “binary” alloy Fe-45Al-0.2B-0.1Zr exhibited predominantly transgranular fracture. Ternary alloying additons with atomic numbers less than that of Fe tended to enhance intergranular fracture, whereas those with atomic numbers higher than that of Fe favored substantial amounts of transgranular fracture. Tensile testing in a partial pressure of dry oxygen increased the ductilities of the ternary alloys only slightly, whereas the ductility of the binary alloy increased from about 8 to about 19%. The ductilities in air correlated inversely with the yield strength. However, those alloys exhibiting substantial amounts of transgranular fracture always showed higher ductilities than those fracturing intergranularly. We interpret our fracture results in terms of yield strengths and ternary element site occupations.

High quality epitaxial BaTiO3 and SrTiO3 have been grown on MgO, stabilized at a one unit cell height, and grown to film thicknesses of 0.5 - 0.7 μm. These relatively thick films remain adherent when thermally cycled between growth temperatures and room temperature, are crack free with high optical quality, and have both in-plane and out-of-plane X-ray rocking curves of 0.3–0.5°. These films have been grown using molecular beam epitaxy (MBE) methods starting with the TiO2 layer of the perovskite structure. The TiO2-Iayer/MgO interface uniquely satisfies electrostatic requirements for perovskite heteroepitaxy and provides the template structure that leads to the high quality films that are obtained. Wavelength dependence of optical loss has been characterized between 475 nm and 705 nm with loss coefficients < 1dB/cm being obtained at the He-Ne wavelength.

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...

We observe that the crystal-truncation-rod (CTR) diffraction from the ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ substrate of an ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$/${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$(001) interface has fine structure when the x-ray energy is tuned through the Cr K absorption edge. This fine structure is attributed to interference between scattering from the substrate and Cr atoms at the interface, which are coherent with the substrate. Comparisons with x-ray-absorption spectra of standard samples demonstrate that the Cr at the interface is predominantly in the ${\mathrm{Cr}}^{3+}$ oxidation state. We demonstrate how the near-edge energy dependence of the CTR diffracted intensity may be used to deduce the amplitude and phase of the interface scattering. This phase information is used in conjunction with reciprocal-lattice-vector-dependent measurements of diffracted power due to CTR's to deduce the structure of the ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$/${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ interface. While the local atomic coordination at the interface is the same as that of ${\mathrm{Al}}_{2}$${\mathrm{O}}_{3}$ and ${\mathrm{Cr}}_{2}$${\mathrm{O}}_{3}$, there is a stacking fault at the interface covering half of the interface area.

At cryogenic temperatures, the accumulation of vacancy-interstitial pairs in Al2O3 from atomic displacements associated with ion implantation produces amorphization. At room temperature, these pairs recombine, and amorphization occurs only at high doses. X-ray reflectivity measurements show that amorphization of the surface of Al2O3 implanted at room temperature with 160 keV Cr+ ions is preceded by a progressive reduction in near-surface density. Monte Carlo simulations show that this density reduction can be accounted for by high-energy-transfer collisions which knock atoms deep into the target, leaving widely separated vacancies and interstitials, which do not recombine. Electron microscopy shows that at least some of these vacancies condense into voids. We propose that this reduction in near-surface density can lead to amorphization at high doses. We present simple approximations for the density reduction expected for different ions and targets.

Ba2RENbO6 (RE = rare earth elements including Y) compounds are considered new additives for superior flux-pinning in YBa2Cu3O7-δ (YBCO) films due to their excellent chemical inertness to and large lattice mismatches with YBCO. Simultaneous laser ablation of a YBCO target and a Nb metal foil attached to the surface of the target resulted in epitaxial growth of YBCO films having columnar defects comprised of self-aligned Ba2YNbO6 (BYNO) nanorods parallel to the c-axis of the film. Compared to pure YBCO, YBCO+BYNO films exhibited no Tc reduction as well as superior Jc performance with higher self- and in-field Jc by a factor of 1.5–7 and also exhibited a strong Jc peak for H∥c indicative of strong c-axis correlated flux-pinning.

Systematic effects of Zr additions on the structural and flux pinning properties of YBa{sub 2}Cu{sub 3}O{sub 7-{delta}} (YBCO) films deposited by metal-organic chemical vapor deposition (MOCVD) have been investigated. Detailed characterization, conducted by coordinated transport, x-ray diffraction, scanning and transmission electron microscopy analyses, and imaging Raman microscopy have revealed trends in the resulting property/performance correlations of these films with respect to varying mole percentages (mol%) of added Zr. For compositions {le} 7.5 mol%, Zr additions lead to improved in-field critical current density, as well as extra correlated pinning along the c-axis direction of the YBCO films via the formation of columnar, self-assembled stacks of BaZrO{sub 3} nanodots.

Nanostructural modulation in the cap layer used in coated conductors can be a potential source for nucleating microstructural defects into the superconducting layer for improving the flux-pinning. We report on the successful fabrication of phase separated, epitaxial, nanostructured films comprised of LaMnO3 (LMO) and MgO via pulsed laser deposition (PLD) on biaxially-textured MgO metallic templates with a LMO buffer layer. Scanning Auger compositional mapping and transmission electron microscopy cross sectional images confirm the nanoscale, spatial modulation corresponding to the nanostructured phase separation in the film. YBa2Cu3O7-δ films (0.8 µm thick) grown using PLD on such phase separated, nanostructured cap layers show reduced field dependence of the critical current density with an α value of ~0.38 (in Jc~H-α).

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.

We have formed BaZrO3 nanocolumns and (Gd,Y)2O3 nanoprecipitates in reel-to-reel metal organic chemical vapor deposition (MOCVD) processed (Gd,Y)Ba2Cu3O7−x coated conductors and increased the critical currents (Ic) of the conductors in applied magnetic fields to remarkable levels. A (Gd,Y)Ba2Cu3O7−x tape of 1 m in length with 6.5% Zr-additions and 30% composition rich in both Gd and Y showed Ic values of 813 A/cm width at (self-field, 77 K) and above 186 A/cm width at (1 T, 77 K). The strongly enhanced flux pinning over a wide range of magnetic field orientations can be attributed to the bidirectionally aligned defect structures of BaZrO3 and (Gd,Y)2O3 created by optimized MOCVD conditions.

We used anomalous x-ray-diffraction methods to measure the contribution of an epitaxial copper overlayer on silicon to the crystal truncation rods (CTR's). The intensities of the CTR's are analyzed to determine interface structure; the epitaxy of a large-misfit system, Cu on Si(111), can be described in relationship to this structure. Anomalous scattering observed at the Cu K edge along a Si CTR demonstrates copper atoms to be in registry with the Si(111) surface. The copper-atom registry at the interface can be modeled based on the known bulk \ensuremath{\eta}-${\mathrm{Cu}}_{3}$Si structure and observed epitaxy.

Interface structures between Si(111) and thick noble metal overlayers are studied by grazing-angle-incidence x-ray diffraction and crystal truncation rods. The 7×7 reconstruction is only preserved under a Ag film deposited at room temperature. This capped 7×7 structure changed to a 1×1 structure upon annealing over 250°C. A thick overlayer of room temperature deposited Au film destroyed the 7×7 reconstruction and changed the interface structure to 1×1. Our results are compared to a thick Cu/Si(111) interface structure1.

The morphology of diamond films grown by activated chemical vapor deposition, (CVD), varies greatly depending on the deposition conditions [1–6]. Small changes in the deposition conditions can cause major changes in the film morphology and crystal perfection. Areas a few millimeters apart in a film may be quite different unless considerable care is taken to ensure uniform deposition conditions. Because the properties of diamond films are strongly dependent upon the crystallite size, orientation, and perfection, it is important to understand the way in which growth conditions affect the film structure in order to design and optimize films for specific applications.

X-ray scattering data obtained for multiple wavelengths with synchrotron radiation were analyzed by the Rietveld method to determine Ni and Pd distributions on the Cu(000) and Au(½½½) sites in the CuAuI tetragonal P4/mmm structure. Alloys of CuAuxM1-x containing 6 at. % Ni or 10 and 25 at. % Pd were processed to obtain maximum ordering. Nickel is predominantly found on the Cu site and most all the Pd is found on the Au site. The uncertainty in site occupation parameters is discussed for various contributions which affect powder intensity measurements. For highly absorbing materials, an observed powder roughness effect decreases the low angle (2θ) intensities relative to the high 2θ intensities. This effect reduces the reliability of the thermal parameters and obscures a proper description of the thermal motion of the two sublattices. Corrections to the X-ray intensity data for surface roughness/porosity effects reduce uncertainties to about ±1 at. % on the refined value of the site occupations. This use of variable wavelength X-rays with simultaneous refinement of the corresponding data is capable of distinguishing site occupations even between two elements of almost equal scattering factor as, for example, Cu and Ni atoms in this investigation. Chemical phase stability is related to the site occupation parameters.

The degree of long-range order in the trialuminides is determined by X-ray powder diffraction techniques. Long-range order exists to their melting points. For the binary trialuminides Al3Ti, Al73Ti27, and Al3Sc, the degree of long-range order is nearly perfect and is a measure of the lack of mixing of the aluminum atoms onto the sublattice occupied by either Ti or Sc. A calculation of the bond energy between neighboring pairs of atoms from the ordering (melting) temperature is made following the Bragg-Williams mean field theory approach. These bond energies compare favorably with more sophisticated calculations. Bond energies are found to be larger than the energy difference between the crystal structure forms DO22, Ll2, and DO23, and therefore, more relevant to understanding the mechanical and chemical behavior of the trialuminides. Ordering or melting temperatures of these intermetallics reflect the strong Al-metal near-neighbor pair potentials and may provide insights to their brittle properties.

By measuring the intensity profiles along the crystal truncation rods of a Si(001) substrate, we obtain the depth sensitivity necessary for x-ray diffraction measurements of the structure of its interface with a thick GaAs overlayer which is epitaxial to, but not in registry with the substrate. By comparing the diffraction with a model based on a grid of misfit dislocations, we find that the atoms at the interface have a root mean square displacement of 1.09±0.1Å from this ideal structure, and that the interface has a roughness of 2.9±1 Å. The diffraction indicates an anomalously small strain perpendicular to the interface in the GaAs near the interface.

The density n of stacking faults (SFs) in epitaxial YBa2Cu3O7−x (Y123) films, consisting of extra CuO planes, is measured by fitting x-ray diffraction patterns using a random stacking model. The SF density is n=0.068nm−1 in films grown by metal-organic deposition on textured templates and optimized for high Ic. The presence of SF is correlated with pinning of magnetic field (H) applied in the Y123 ab plane. SF can be nearly eliminated by a high temperature anneal, or by adding excess Dy, resulting in Ic which is nearly independent of the orientation of H.

The superconducting grain-boundary (GB) network of coated conductors (CCs) is usually assumed to be a replica of the substrate network. In this letter, we analyze IBAD and RABITS CCs, where such replica either do or do not exist. We have analyzed the effect of GB overgrowth on the critical currents by quantifying the average superconducting grain size and determining the intragrain and grain-boundary critical current densities, JcG and JcGB. We have employed a recently developed inductive methodology enabling the simultaneous determination of these three parameters. We show that the percolative JcGB may be reduced by 50% if the GB networks do not correlate, while JcG and the grain pinning properties appear unaffected.

We report a practical synthesis route for the production of long length, biaxially-oriented high-temperature superconducting (HTS) deposits on metallic tapes. The technique involves epitaxial vapor deposition of appropriate oxide buffer layers on rolled, thermo-mechanically processed fcc-structure base-metal tape substrates. Short segments of ≈1 μm thick YBa2Cu3O7-δ deposits produced by pulsed laser ablation on CeO2 and yttria-stabilized ZrO2 (YSZ) buffered nickel exhibit epitaxial biaxial alignment and have critical current densities over 106 A/cm2 at 77 K in zero applied magnetic field.

We have studied the equilibrium magnetization of magnetically aligned Hg-based cuprate superconductors containing 1, 2, or 3 adjacent Cu−O layers. As the number of layers increased, the deduced carrier doping per Cu−O layer remained nearly constant, while the slope of the upper critical field—dHc2/dT increased linearly.

Epitaxial YBa2Cu3O7-δ (YBCO) films with transport critical current densities approaching 3×106 A/cm2 (77 K, 0 T) were fabricated using laser ablation of YBCO onto rolling-assisted biaxially textured-substrates (RABiTS) using a combination of thin CeO2 and thick YSZ buffer layers. The configuration of the sample was YBCO (∼0.2 µm)/YSZ (0.7 µm)/CeO2 (0.05 µm)/Ni (125 µm). The CeO2 and YSZ buffer layers were deposited using electron-beam evaporation and sputtering, respectively. The temperature window for successful pulsed-laser deposition of YBCO onto RABiTS was found to be between 740°C and 790°C.

High-resolution in situ x-ray-diffraction measurements were made of the lattice constants of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathrm{x}}$ as it was heated and cooled through the orthorhombic-tetragonal transition at a series of ${\mathrm{O}}_{2}$ pressures. The transition is sharp, continuous, and reversible in temperature and pressure. As ${\mathrm{O}}_{2}$ pressure is reduced from 1.0 to 0.005 atm, the transition temperature falls from 676\ifmmode\pm\else\textpm\fi{}5 \ifmmode^\circ\else\textdegree\fi{}C to 521\ifmmode\pm\else\textpm\fi{}10 \ifmmode^\circ\else\textdegree\fi{}C while oxygen content at the transition falls from 6.66\ifmmode\pm\else\textpm\fi{}0.01 to 6.59\ifmmode\pm\else\textpm\fi{}0.02. Dilation along the c axis is observed as oxygen is removed. Under helium, an irreversible but time-dependent orthorhombic-to-tetragonal transition occurs during heating.

Neutron powder diffraction has been used to refine the structure of the high- T c superconductor Tl 2 Ca 1 Ba 2 Cu 2 O 8 to determine the precise oxygen co-ordination and the effective valence of copper. The results are in excellent agreement with the Dupont X-ray structure, confirming the possible substitution of about 9% of the Ca-sites with Tl in our sample. The Tl-sites may be either 3% Tl-deficient or 7% Ca-substituted. The apparent valence of copper is 2.22. Oxygen in the center of the Tl square implies an average valence of less than 3 for Tl, and it is therefore not suprising that this oxygen is desordered toward the mid-point of the shortest Tl-Tl distance. High resolution electron images and diffraction reveal a quite different superstructure to the 5 x 5.4 A superstructure seen in Bi 2 Sr 1 Ca 2 Cu 2 O 8 . Very weak and diffuse superlattice spots may be due to a charge density wave in the TlO plane with period 6 x 3.8 A.

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)

The solidification behavior of two low-melting-point metals, Sn and In, on three substrates has been examined using in situ x-ray diffraction. Undercoolings of up to 56.1°C were observed for Sn solidified on graphite, which is a nonwetting substrate, while lower undercoolings were observed for Sn on Au/Ni/Cu (17.3°C) and on Cu (10.5°C). Indium behaved quite differently, showing undercoolings of less than 4°C on all three substrates. The lattice expansion/contraction behavior of Sn, In, and intermetallic compounds (IMCs) that formed during the reaction of Sn with Au/Ni/Cu surfaces were also measured during heating and cooling. Results showed anisotropic and nonlinear expansion of both Sn and In, with a contraction, rather than expansion, of the basal planes of In during heating. The principal IMC that formed between Sn and the Au/Ni/Cu surface was characterized as Cu6Sn5, having an average expansion coefficient of 13.6 × 10−6/°C, which is less than that of Sn or Cu.

Bulk sintered and powdered samples of the high-temperature superconductive compounds ${\mathrm{Tl}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{1+\mathrm{\ensuremath{\delta}}}$ (Tl-2:2:2:3) and ${\mathrm{Tl}}_{2}$${\mathrm{Ca}}_{2}$${\mathrm{Ba}}_{2}$${\mathrm{Cu}}_{2}$${\mathrm{O}}_{8+\mathrm{\ensuremath{\delta}}}$ (Tl-2:1:2:2) have been synthesized with phase purity of approximately 90%. The materials were characterized by x-ray-diffraction, metallographic, and electron microprobe analyses. The electronic and superconductive properties were investigated through measurement of the electrical resistivity and the critical current density ${J}_{c}$ using transport methods and by extensive magnetization measurements. Primary results and conclusions are that (1) the intragrain ${J}_{c}$ values were large, much larger than the transport values; (2) both sintered and powdered materials exhibited large flux creep; (3) and the ${J}_{c}$ decreased exponentially with temperature. These features are qualitatively very similar to those found in the corresponding ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{\mathrm{z}}$ (with z\ensuremath{\approxeq}7) series of compounds.

Although high critical current density (J c ) YBCO can be deposited on rolling assisted biaxially-textured substrates (RABiTS) with the YSZ/CeO2/Ni architecture, improvement in uniformity is needed due to the presence of two-component YBCO epitaxy and cracking in the CeO2 buffer. We have determined that Yb2O3 is an excellent buffer material that provides a single-component YBCO epitaxy. In addition, crack-free epitaxial Y2O3 can be consistently deposited onto textured Ni substrates. High quality YBCO films have been deposited, and J c as high as 1.8 ×106 A/cm2 at 77 K has been obtained on this Yb2O3/Y2O3/Ni alternative RABiTS architecture.

The syntheses of Cu(PO3)2, Cu2P2O7, Cu4P2O9, Cu5P2O10, Cu3(PO4)2, and Cu2PO4 were accomplished by several new solid-state routes. Attempts to synthesize CuPO3 were unsuccessful, and it is suspected that this compound, which is reported in the literature, may not exist. The thermal stabilities of Cu(PO3)2, Cu2P2O7 and Cu3(PO4)2 were examined, and their decomposition was concluded to be strongly dependent on slow kinetics.

Cobalt phosphates have been synthesized and their thermal behavior examined. The formation of compounds and solid solutions among cobalt and copper phosphates is studied by X-ray diffraction. Unlimited solubility exists between the pyrophosphates Co2P2O7 and Cu2P2O7, the orthophosphates Co3(PO4)2 and Cu3(PO4)2, and Co3(PO4)2 and Cu2P2O7. X-ray diffraction indicates that the structures of cobalt and copper pyrophosphate solid solutions vary gradually from one end member to the other. The structures of orthophosphate solid solutions vary in a more complex manner: the change is gradual from Co3(PO4)2 to Co2Cu(PO4)2. At Co1.5Cu1.5(PO4)2, a new structure (L) occurs. At 950°C, CoCu2(PO4)2 also exhibits this structure, which is similar to that of graftonite, Fe3(PO4)2. CoCu2(PO4)2 is dimorphic, changing reversibly at 1000°C to a triclinic structure (H) related to that of Cu3(PO4)2. From CoCu2(PO4)2 (H) to Cu3(PO4)2, the structure appears to vary gradually. A new phosphate, Cu+Cu2+Co3(PO4)3, has also been synthesized.