Y-Ba-Cu-O films were made by R-F diode sputtering using a single oxide target. It was found that if a small negative bias is applied to the substrate, the etching associated with reactive sputtering is significantly reduced. This results in better composition control and uniformity, which are quite important for the formation of superconducting thin films. Films deposited on strontium titanate, when annealed in oxygen, become superconducting with zero resistance at 89 K.

It is observed that in sol-gel derived oxide systems, chemical processes lead to the formation of photoluminescent centers analogous to those produced by neutron or γ-irradiation of oxide crystals, fused silica, and other glasses. The initial observations about the phenomenon and its proposed mechanism are reported here.

We have performed Rutherford backscattering spectrometry, non-Rutherford proton elastic scattering, and axial ion channeling analysis to determine the composition, the crystallinity, and the epitaxial quality of YBa2Cu3O7 superconducting thin films on (100) SrTiO3 and (100) yttria stabilized zirconia (YSZ) substrates. YBa2Cu3O7 superconducting thin films were fabricated both by high and low temperature laser ablation techniques. The former method requires high temperature annealing in oxygen to recover the superconducting properties, whereas in the latter method as-deposited in situ superconducting thin films are formed at low processing temperatures (500 °C–650 °C). Helium ions in the energy range of 2.0–2.5 MeV were used to determine the relative stoichiometries of the heavier atomic number elements (Y, Ba, Cu) in the film, but are not sensitive enough to determine the relative amount of oxygen in the superconducting phase. The detection sensitivities to oxygen can be greatly enhanced by using the proton elastic scattering [16O(p,p) 16O] reaction, which was found to increase the scattering cross section by a factor of 3 to 5 relative to the Rutherford scattering cross section. The ion-channeling of YBa2Cu3O7 superconducting thin films on (100) SrTiO3 substrates showed excellent minimum channeling yields corresponding to epitaxial growth, but the presence of defects increased the channeling yields for films deposited on (100) YSZ substrates. The ion channeling yields are compared with the microstructure of the films determined by transmission electron microscopy.

Superconducting Bi-Sr-Ca-Cu-O thin films have been prepared for the first time by chemical vapor deposition using triphenyl bismuth and fluorocarbon-based chelates such as bis(hexafluoroacetylacetonate)strontium, bis(hexafluoroacetylacetonate)calcium, and bis(hexafluoroacetylacetonate)copper. After annealing in air, x-ray diffraction data reveal that the films deposited on (001) SrTiO3 substrates have preferential orientation of their crystalline c-axis perpendicular to the substrate surface. Four-probe resistivity measurements reveal the onset of superconductivity at 80 K and zero resistivity at 50 K.

ZnSe layers have been grown by molecular beam epitaxy on high-purity, high-quality ZnSe wafers [(100) oriented] cut from ingots grown by the iodine vapor transport method. Photoluminescence (PL) analysis indicates the homoepitaxial ZnSe material to be of ultra-high purity as well as being strain-free relative to ZnSe/(100) GaAs layers which exhibit in-plane biaxial tension. The 10 K PL spectra recorded from homoepitaxial layers exhibit unsplit free- and donor-bound exciton transitions of comparable intensity together with a strong peak at 2.7768 eV believed to be the so-called Iv transition in relaxed ZnSc. The ultra-high purity nature of the homoepitaxial layers is attributed to the high purity of the substrate material in addition to the use of high purity Zn and Se source materials in this work.

We describe a hypothetical new phase of carbon. The proposed structure is a rigid three-dimensional network with sp2 (threefold) coordination only. Tight-binding calculations indicate that the proposed material is a metastable metal significantly harder than diamond. Although it is unclear at present whether such a material can be produced in significant quantity, we speculate that it (and related structures) plays a role in the chemical vapor deposition of diamond films.

Using several measured and calculated physical properties, we argue that the high-Tc metal-oxide superconductor Y1Ba2Cu3O7 is elastically soft compared with BaTiO3 or SrTiO3. We conclude that the bulk modulus equals approximately 107 GPa, despite several high-pressure x-ray diffraction studies that report values up to approximately 200 GPa. Part of the argument uses an ionic-crystal-model calculation of the bulk modulus.

The creep behavior of Mg–14Li particulate composites containing 0,10,20, and 30 vol. % boron particles was evaluated from 230 to 280°C. The results reveal that the creep strength of the particulate composite is increased by a factor of eight over the Mg–14Li matrix with the addition of 30 vol. % boron. The body-centered cubic (bcc) Mg–14Li alloy is shown, however, to be much weaker than hexagonal close-packed (hep) pure magnesium. This difference is attributed to the high rate of atom mobility in the open structure of the Mg–14Li bcc alloy. It is predicted that a Mg–6Li–30B particulate composite, containing an hep matrix structure, will have a higher specific strength at 250°C than the new experimental aluminum base–high iron alloys prepared by rapid solidification processing.

The crystalline perfection of microwave plasma assisted chemical vapor deposited (MPACVD) diamond films grown under various conditions has been examined by TEM. Most CVD diamond films thus far reported contain a high density of defects, predominantly twins and stacking faults on {111} planes. We show that under appropriate growth conditions, these planar defects are eliminated from the center of the crystallites, and occur only at grain boundaries where the growing crystallites meet.

We report the development of a reaction technique which yields ceramic Nd1.85Ce0.15CuO4−y with macroscopically uniform concentrations of Ce and O. Under appropriate argon annealing conditions, samples exhibiting bulk superconductivity as gauged by resistive transition width and diamagnetic shielding are obtained. In addition. metallic behavior, indicated by positive dp/dT above Tc, is obtained for the normal state.

Large-scale twin structures in single crystal Bi2Ca1Sr2Cu2O8 (2122) are reported for the first time. Symmetrical 90° (i.e., a-b) twins with a [110] type twin boundary were observed. A characteristic layer-growth morphology and jagged twin walls suggest that twin formation occurred layer by layer during crystal growth; i.e., the twins were growth twins. Hot-stage optical microscopy, x-ray diffraction, and electron microscopy results are discussed with reference to twin morphology.

High quality bulk YBa2Cu3O7−x was synthesized by fusing stoichiometric amounts of yttrium and copper nitrates and barium hydroxide in air, using an ordinary Bunsen burner. The starting materials go through a short-lived liquid phase yielding a solid black product which was subsequently heat treated (900 °C, 18–24 h in air, followed by 500 °C, 5 h in O2). These materials were greater than 99% phase pure with CuO as the only other phase and they exhibited a transition temperature of 92 K, a 15.5% perfect diamagnet response (field cooled). This synthesis represents an improvement over the much more labor and time intensive conventional methods in that it allows high quality materials of various compositions to be prepared quickly.

The critical current density Jc of superconductors is strongly dependent on microstructure. The microstructure and crystallization of amorphous Nb75Ge24.5B0.5 melt spun ribbons were studied as a function of 24-h anneals between 680 and 860 °C. Metastable A15 was formed with a composition close to that of the starting amorphous material. As the temperature increased from 680 to 720°C, crystallization remained nonuniform and the average grain size decreased from 130 nm to 60 nm. Between 740 and 800°C crystallization was uniform and the average grain size was constant at 30 nm. Above 820°C grain growth occurred. In order to have high Jc's a uniformly crystallized small-grained material is desirable.

We report the results of a systematic examination of the lattice parameters for the YBa2Cu3O7 compound in the 100 K to 110 K temperature range by means of high resolution synchrotron x-ray powder diffraction techniques. The data indicate a linear decrease in the lattice parameters with decreasing temperature over this temperature range. An observed asymmetric broadening of the diffraction peaks is explained by the presence of residual stress in the lattice.

High Tc Tl–Ba–Ca–Cu–O (A) and Tl–Ba–Sr–Ca–Cu–O (B) superconducting filaments were successfully prepared using a technique in which suspension spun and pyrolyzed filaments were densified by pressing and sintering. A zero resistance state was achieved at 112 K and 106 K, and the maximum Jc at 77 K, 0 T was 1200 A/cm2 and 2300 A/cm2 for Tl–Ba–Ca–Cu–O (A) and Tl–Ba–Sr–Ca–Cu–O (B) filaments, respectively. Although the starting powder had a high Tc phase of Tl2Ba2Ca2Cu3Ox, the structure of the filament with high Jc was a high Tc phase of Tl1Ba2Ca2Cu3Ox, due to the volatility of Tl oxide from the large surface area of the filament.

Amorphous lead iron tungstate was prepared from the melt by twin-roller quenching. The rapidly solidified material was characterized in terms of density, x-ray diffraction, differential thermal analysis, and electrical properties. Results are given for the amorphous-crystalline transformation.

A series of diamond polytype structures are described and their IR and Raman vibrational modes predicted. The diamond polytypes are analogous to the well-known silicon carbide polytypes. The intermediate 6H diamond polytype was recently identified by single crystal electron diffraction of vapor precipitated diamond powder. In addition, end member polytypes of 3C (cubic diamond) and 2H diamond (hexagonal lonsdaleite) have been previously established, and polytypes such as 4H, 8H, 15R, and 21R diamond are predicted, but may be difficult to isolate and identify. The various diamond polytype structures differ only in the stacking sequences of identical puckered hexagonal carbon layers. These identical carbon layers lie parallel to the cubic 3C {111} and the hexagonal 2H {001} planes. A new method for uniquely labeling the structural layers in the polytype stacking sequences is presented. Factor group analysis was used to determine the IR and Raman selection rules for five diamond polytypes with structures intermediate between those of end members diamond and lonsdaleite. Brillouin zone folding techniques were used to determine band positions, in analogy with analyses of SiC polytypes discussed in the literature. The results predict that (i) all diamond polytypes are Raman active, (ii) limiting polytypes 3C and 2H are not IR active, and (iii) polytypes 4H, 6H, 8H, 15R, and 21R have IR active modes.

The stability of YBa2Cu3O7−x superconductors toward reactions with CO2 in CO2/O2 gas mixtures has been studied during annealing at temperatures ranging from 600°C to 950°C. The results show that there are three different types of the reactions. The reaction products of these reactions all include BaCO3 and CuO, while the third product is dependent on the annealing temperature. At 600°C, YBa-carbonates were formed while Y2Cu2O5 and Y2BaCuO5 were formed at 815°C and 950°C, respectively. Transmission Electron Microscopy images show that the reactions started at grain boundaries with the formation of island-type precipitates.

Transmission electron microscopy of two-phase V-Hf-Nb and V-Hf-Nb-Ti alloys plastically deformed at room temperature shows that {111} (112) twinning is a major deformation mode for the HfV2-based Laves phase. Bands of concentrated shear are also observed. Possible approaches to enhance low-temperature deformability in other Laves phases are discussed.

A single-wafer multiprocessing technology has been developed based on the use of lamp heating and remote microwave plasma process energy sources for fabrication of in-situ-doped homoepitaxial Si and heteroepitaxial Si/GexSi1−x multilayer structures via chemical-vapor deposition. Some effective low-temperature (650°–800°C) processes were developed for in-situ pre-epitaxial growth surface cleaning. These chemical cleaning processes employ GeH4 + H2 or GeH4 + H2 + (HF or HCl) gas mixtures with very small GeH4-to-H2 gas flow rate ratios. Multilayer heteroepitaxial structures with controlled doping and Ge fractions consisting of strained Ge4Si1−x layers were fabricated and characterized.