Regrowth of ion-damaged YBa2Cu3O7−δ thin films on LaAlO3 was studied using the ion beam channeling technique. The damaged films can be regrown at a temperature as low as 650 °C, and are stable up to 1000 °C. The regrowth process was found to be thermally activated with a single activation energy of 0.46 eV, contrary to two energies found in a previous study on the films on MgO [J. A. Martinez et al., Appl. Phys. Lett. 57, 189 (1990)].

For all tetrahedrally bonded semiconductors (five group IV plus nine III-V compounds and nine II-VI compounds), it is shown that the critical pressure needed to transform the semiconductor into the metallic state correlates with the microindentation hardness number. The same is done for five alkaline earth oxides. The critical transition pressures have been estimated from Herzfeld's theory—that is, from the compression at which the dielectric constant diverges to infinity. Experimental transition pressures also correlate with hardness numbers, and they correlate with the activation energies for dislocation motion. Since these transitions are electronic they can be influenced by photons, doping (donors enhance while acceptors inhibit them), currents, surface states, etc. Microindentation also provides a simple experimental tool for observing pressure and/or shear induced transformations.

The absorption coefficient of β–SiC is measured by the transmission technique. β–SiC films are grown on Si substrates by chemical vapor deposition using a buffer layer between β–SiC and the substrate. The absorption coefficient value ranges from 10 to 5.5 × 104 cm−1 in the energy range between 2.42 and 4.4 eV. The bandgap of β–SiC films investigated in this study ranges between 2.13 and 2.32 eV.

Epitaxial BaTi3 films have been grown on NdGaO3 [100] substrates by reduced pressure MOCVD for the first time. The substrate temperature was 1000 °C and the total pressure was 4 Torr. Electron and x-ray diffraction measurements indicate highly textured, single phase films on the NdGaO3 substrate which are predominantly [100], with [110] also present. TEM and selected area electron diffraction (SAED) indicate two specific orientational relationships between the [110] and the [001] diffraction patterns.

A new sol-gel method for the preparation of ZnO varistor powders, using inexpensive source materials such as acetates and nitrates, is described. It yields powders with a more homogeneous distribution of dopants compared to the commercially used mixed oxide technique. Varistor ceramics made from sol-gel powders can be sintered at lower temperatures and show improved electrical behavior. This is a consequence of formation of more varistor-active grain boundaries within the ceramics.

The preferred orientation of a series of laser deposited superconducting thin films of YBa2Cu3O7−δ on LaAlO3 substrate has been examined. X-ray measurements (pole figures, χ-scans, ω-scans, rocking curves) reveal an increasingly strong preferred orientation of the polycrystalline material with c-axes perpendicular to the substrate surface as deposition temperature increases. At low temperatures c-axes are predominantly parallel to the substrate surface. Characteristic parameters of the texture types were derived from those measurements. With higher temperatures twinning on (110) was observed. The different texture types are interpreted in terms of a layered film structure.

YBa2Cu3O6+δ microcrystals are synthesized by extraction of a nonstoichiometric melt similar to that employed for crystal growth of this compound. This method uses, first, initial compositions corresponding to the field YBa2Cu3O6+δ plus liquid, and second, the interaction properties of the flux with an appropriate substrate, i.e., Y2O3. Using other substrates like alumina produces 123 microcrystals, but embedded in the residual flux; in contrast yttrium oxide reacts with this one, and it is essential for its extraction. Choosing proper conditions makes it possible to obtain relatively pure YBa2Cu3O6+δ samples made of regular pellets (size: 10 to 20 μm thickness: 3 to 6 μm). The process is discussed using the phase diagram and the concept of dissolution-reprecipitation often involved in liquid phase sintering.

Electron paramagnetic resonance (EPR) studies of pure Y2BaCuO5 in powder and single crystal forms and of YBa2Cu3O7−δ in powder and single crystal forms provide further evidence that it is Y2BaCuO5 that is the common green impurity found in many preparations of YBa2Cu3O7−δ as a powder or in pellet forms. Y2BaCuO5 tends to be excluded in the growth of YBa2Cu3O7−δ single crystals. A method is presented for the growth of Y2BaCuO5 crystals from a flux. An apparent discrepancy between the observed single crystal EPR anisotropy and the reported crystal structure is resolved in three independent ways from the Y2BaCuO5 Powder and single crystal EPR data. These results show that the EPR spectrum is a superposition of the spectra of the two differently oriented Cu sites in the unit cell and is not a spectral average of them. The temperature independence of the EPR spectrum between 150 K and 300 K is also consistent with there being no temperature dependent exchange averaging of the EPR spectra of the two sites in this range. The orientations of the Cu crystal field axes, as indicated by the g axes, are in agreement with the crystal structure. Crystal field splittings of the Cu d-orbitals are estimated from the measured g values and indicate an appreciable covalency in the Cu–O bonds. The linewidth and its anisotropy indicate a minor degree of exchange narrowing.

A range of copper-rich bulk YBa2Cu3+xO7+y superconductors have been prepared by mixing excess copper oxide in the initial material and characterized for their magnetic properties and microstructure. The microstructure of the materials exhibits a high density of planar defects at the grain boundaries and a grain boundary amorphous phase. There is a small increase in the magnetic Jc at 4.5 K but a decrease compared to a conventional material at 77 K, and there is no correlation of the magnetic Jc with the twin boundary density. The change in Jc can be understood if the grain boundary pinning is strong at 4.5 K but weak at 77 K. Data obtained using a very wide range of different microstructure characterization techniques clearly indicate the dangers of relying on only one technique to obtain a full picture of the material.

We have used scanning electron microscopy (SEM) and energy dispersive x-ray spectroscopy (EDS) to study compositional homogeneity at several stages in the processing of powders to the Ba2YCu3Ox high Tc superconductor. We investigated the effects of solution pH and ionic concentration in the precipitation preparation of mixed hydroxycarbonates of Ba, Y, and Cu as precursor to the Ba2YCu3O7−x high Tc superconductor. Our results show that both powder homogeneity and particle morphology are strongly dependent on these parameters. Additionally, studies of the compacted powders by EDS mapping at successive stages of processing show the development of phase inhomogeneities even in homogeneous starting powders.

Thick Bi2Sr2CaCu2O8 films have been produced by melting Bi2Sr2CaCu2O8 powder on MgO substrates at temperatures just above the melting temperature of the powder. X-ray diffraction measurements indicate enhanced c-axis alignment throughout the thickness of the films. Films melted at 900 °C show greater alignment and contain less Bi2Sr2CuO6 compared to those processed at 950 °C. Both the degree of alignment and the Bi2Sr2CuO6 content increase as the cooling rate is decreased. Transport measurements show that films quickly cooled from low melt-processing temperatures have the highest critical current densities (Jc = 13 kA/cm2 at 30 K). The temperature dependence of Jc is best described by a flux creep model. Finally, Jc at 4.2 K (in both parallel and perpendicular magnetic fields) undergoes a sudden drop at low fields, but levels off above 0.5 T to about 30% of the zero field value.

Recent experiments on promising high-temperature aluminide intermetallic compounds discovered that, in contrast to NiAl, RuAl has critical 〈111〉 slip systems that facilitate ductility under compression at room temperature. In order to understand this different mechanical property from a microscopic point of view, the cohesive and electronic properties of NiAl and RuAl have been studied by means of the first principles local density all-electron self-consistent linearized muffin-tin orbital (LMTO) and full-potential linearized augmented plane wave (FLAPW) methods. The ground state cohesive properties calculated by the LMTO method (including equilibrium lattice constant, bulk modulus, and formation energy) are found to be in good agreement with experiment. The analysis of the band structure and density of states shows that the transition metal (Ni or Ru) d-Al p hybridization provides the major contribution to the cohesive energy in both compounds. The anti-phase boundary (APB) energy of RuAl associated with the ½〈111〉 {110} superdislocation (580 mJ/m2) is found to be only 65% that of NiAl. Moreover, the charge density near the Fermi energy reveals that (i) the strong Ni d-Al p hybridization at EF for NiAl causes a directional charge distribution along the 〈111〉 direction which may affect its dislocation dissociation; (ii) for RuAl, a mostly Ru-d electron charge distribution shows only d-d bonding along the 〈100〉 direction between Ru atoms.

Tensile testing of cast and extruded binary NiAl was performed from 300 to 900 K at strain rates of 1.4 × 10−4 to 1.4 × 10−1 × s−1. The brittle-to-ductile transition temperature (BDTT) was dependent on strain rate, with a three order of magnitude increase in strain rate resulting in approximately a 200 K increase in transition temperature. Regardless of strain rate, at temperatures just above the BDTT the fracture strength increased significantly and the fracture morphology changed from mostly intergranular to predominantly transgranular. It was also determined that the mechanism responsible for the brittle-to-ductile transition in NiAl had an apparent activation energy of approximately 118 kJ/mol. These results support the argument that the mechanism for the brittle-to-ductile transition in NiAl is associated with the onset of a thermally activated deformation process. This process is probably dislocation climb controlled by short circuit diffusion.

Results of Sneddon's analysis for the elastic contact between a rigid, axisymmetric punch and an elastic half space are used to show that a simple relationship exists among the contact stiffness, the contact area, and the elastic modulus that is not dependent on the geometry of the punch. The generality of the relationship has important implications for the measurement of mechanical properties using load and depth sensing indentation techniques and in the measurement of small contact areas such as those encountered in atomic force microscopy.

In this paper the finite element method is used to explore the mechanics of the microindentation process. In the simulations discussed, aluminum and silicon are investigated both in their bulk forms and in thin film-substrate combinations. Among the quantities readily computed using this approach and given in this paper are hardness (computed using actual contact area), contact stiffness, effective composite modulus, and surface profile under load. Importantly, this investigation builds on previous work by providing a more critical examination of the amount of pileup (or sink-in) around the indenter in the fully loaded configuration, as well as the variation of the actual contact area during indenter withdrawal. A key conclusion of this study is that finite element simulations do not support the widely used assumption of constancy of area during unloading (for either bulk materials or thin film systems). Furthermore, the amount of pileup or sink-in can be appreciable. The implication of these findings is that for many situations the commonly used straight-line extrapolation of a plastic depth may render an estimate for the contact area that is quite distinct from the actual area. This assertion is demonstrated herein through comparison of hardnesses calculated using actual contact area with values calculated using the straight-line extrapolation of plastic depth.

Constant load creep experiments were conducted using a depth-sensing indentation instrument with indentation depths in the submicron range. Experiments were conducted on polycrystalline Sn and sputtered Al films on Si substrates. The results show that the plastic depth versus time curves and the strain rate versus stress plots from these experiments are analogous to those obtained from conventional creep experiments using bulk specimens. The value of the stress exponent for Sn is close to the reported values from uniaxial creep tests. Tests on Al films showed that the stress exponent is dependent on the indentation depth and is governed by the proximity to the film/substrate interface. Load change experiments were also performed and the data from these tests were analyzed. It is concluded that indentation creep experiments may be useful in elucidating the deformation properties of materials and in identifying deformation mechanisms.

Johnson and Oh have recently developed Embedded Atom Method potentials for bcc metals (Na, Li, K, V, Nb, Ta, Mo, W, Fe). The predictive power of these potentials was first tested by calculating vacancy formation and migration energies. Due to the results of these calculations, some of the functions were slightly modified to improve their fit to vacancy properties. The modified potentials were then used to calculate phonon dispersion curves, surface relaxations, surface energies, and thermal expansion. In addition, Johnson's alloy model, which works well for fcc metals, was applied to the bcc metals to predict dilute heats of solution.

We present the results of a combined experimental and theoretical investigation of phase separation and microstructure development in co-deposited Al–Ge thin films. For small film thicknesses and deposition temperatures above 150 °C the phase-separated films consist of an array of domains of the Al- and Ge-rich terminal phases (lateral phase separation). Films deposited at 100 °C or less contained one or both of the terminal phases plus a metastable phase. We show that the domain structure evolves during deposition in a manner consistent with a surface interdiffusion controlled process. As film thickness increases we observe a transition from the laterally phase-separated microstructure to a layered microstructure exhibiting phase separation perpendicular to the film/substrate interface (transverse phase separation), with Al segregating to the film surface. We present a thermodynamic argument based on the competition between surface and interfacial free energies to explain this transition. Finally, we discuss the stability of the transverse phase-separated microstructure in the thick-film limit in terms of the transport of Ge through the Al-rich surface layer.

Metal-containing amorphous hydrogenated carbon (Me–C: H) films were prepared on silicon substrates. Two kinds of metals (Ti, Ta) were incorporated in the process of reactive rf diode— (13.56 MHz) and DC-magnetron sputtering, respectively. Elastic recoil detection (ERD) and Rutherford backscattering (RBS) of MeV He+ ions were used to determine the hydrogen content and mass density of Me–C: H films. The mechanical properties, i.e., microhardness, Young's modulus, and adhesion, were measured with the help of a nanoindenter and scratch tester. Results show that (1) the mechanical properties of Me–C: H films depend mainly on metal concentrations. At a certain metal concentration, optimal hardness, Young's modulus, and critical load were obtained; (2) the M–C: H films with an optimal metal concentration possess similar hardness, Young's modulus, and higher critical load compared with the corresponding values of diamond-like carbon (a–C: H) films, due to the improvement of the toughness of the films by the incorporation of metals. Therefore, Me–C: H films show high promise of being wear-resistant protective coatings.

The formation and characterization of zirconia coatings on graphite/carbon filaments were investigated. The objective was to eliminate or minimize degradative chemical reactions and improve bonding at the metal/carbon-fiber interface when the coated fiber is used as reinforcement in metal matrix composites. Thin, homogeneous films of zirconium oxide, ZrO2, less than 1μm thick, were formed on carbon monofilaments (35 μm diameter) from a zirconium oxychloride solution in water (less than 1.0 wt. % ZrO2) by dip coating and heating. Chemical changes during thermal decomposition and polycondensation were examined by FTIR spectroscopy. Through dynamic x-ray diffraction tests, the zirconia coating was found to transform first to a metastable tetragonal phase on heating to 330 °C, and then upon cooling, to a stable monoclinic structure. Organotitanate coatings were formed by electrodeposition of the ionizable organometallic complex, titanium di(dioctylpyrophosphate) oxyacetate (TDPA). Single fiber tests revealed a slight reduction in the strength of fibers with thicker coatings, probably due to crack initiation by brittle fracture of the ZrO2 coating. Thin coatings applied from 0.25% ZrOCl2 did not cause such strength reduction. Effective bonding of ZrO2 coatings to the filaments was revealed in single filament composite tests which showed the interfacial shear strength (IFSS) of the coated filaments in an epoxy matrix to be higher than that of the uncoated filaments. The IFSS of monofilaments electrocoated by the titanate was also higher. Examination of the fracture surfaces showed fiber pull-out associated with poor bonding in the case of specimens prepared from uncoated monofilaments. The coated monofilaments showed no fiber pull-out, suggesting that maximum fiber strength was achieved and transferred through the interface to the matrix. Finally, the chemical and thermal stability of the interfacial region of coated and uncoated graphite rods embedded in an aluminum matrix were evaluated. The uncoated rod showed little or no interfacial bonding to the metal matrix, suggesting poor wetting, while the dip-coated and electrocoated rods showed good wetting and compatibility with the metal matrix.