YBa2Cu3O7−x (YBCO) superconducting thin films that show no x-ray diffraction peaks due to any other non-superconducting phases have been synthesized by annealing Y-Ba-Cu-O amorphous precursors at 750 °C. The Y-Ba-Cu-O precursors have been fabricated by oxidizing Y-Ba-Cu metallic precursors coevaporated from Y, Ba, and Cu metallic sources under ultrahigh vacuum conditions. Crystallization behavior from the Y-Ba-Cu-O precursor to YBCO films drastically depends on an oxidation temperature for the Y-Ba-Cu metallic precursor. YBCO thin film synthesized from the precursor oxidized at an optimum temperature shows a zero resistance temperature of over 80 K and a very smooth surface.

Surface modification is achieved by coating the aluminum surface with a powder mix of {Si + flux + a metal (Me)} and heating at ∼600 °C for a time interval of the order of 1 min. During heating, the flux melts and dissolves the native surface oxide film on aluminum, thus allowing Si to react with the substrate to form a film of liquid Al-Si alloy of near-eutectic composition. The component Me of the powder coating then reacts with the molten metal layer to modify the metallurgical properties of the surface after solidification.

Calculations predict that carbon nanotubes may exist as either semimetals or semiconductors, depending on diameter and degree of helicity. This communication presents experimental evidence supporting the calculations. Scanning tunneling microscopy and spectroscopy (STM-S) data taken in air on nanotubes with outer diameters from 17 to 90 Å show evidence of one-dimensional behavior; the current-voltage (I-V) characteristics are consistent with a density of states containing Van Hove type singularities for which the energies vary linearly with inverse nanotube diameter.

In order to overcome the difficulty of nucleation of diamond particles on unscratched substrates by the chemical vapor deposition (CVD) method, carbon fibers are introduced on unscratched substrates as a nucleation site of diamond particles. With assistance of carbon fibers, diamond particles can be synthesized on unscratched silicon substrate from a gas mixture of methane and hydrogen by the hot-filament CVD method. From SEM observations, nucleation of diamond particles has been confirmed on fibers at the beginning of deposition. Fine particles have formed initially on the rugged surface of fibers, and then they grow up to be diamond particles. Detailed SEM observations reveal nucleation has occurred on irregular surfaces such as boundaries on carbon fibers. We propose that nucleation of diamond particles can be controlled by arranging carbon fibers on the substrate without applying any mechanical pretreatment.

Monophasic β-SiC powder has been synthesized in a commercial microwave oven operating at 2450 MHz and power levels up to 980 W. This simple method of solid-state synthesis involves a direct reaction between silicon and charcoal powder at temperatures lower than 1250 K.

We report the observation of fractal patterns in C60-tetracyanoquinodimethane thin films. The fractal patterns and their microscopic features are described and characterized. The fractal dimension was determined to be 1.69 ± 0.07. According to the characterization results, the observed fractals are compared to the cluster-diffusion-limited-aggregation model. The growth of the fractal patterns in the thin films is also in terms of the existing long-range correlation.

High oxygen pressures have been achieved in a piston-cylinder apparatus using a double capsule assembly consisting of a sealed outer Au capsule, containing an oxygen source (KMnO4), and an inner, open Pt capsule containing the sample. Using this technique, La2CuO4 was annealed at 800 °C, 5–25 kbar for 2–4 h. Transposed temperature drop calorimetry at 704 °C was used to determine the enthalpy of oxidation, and weight loss measurements characterized the oxygen nonstoichiometry, δ, in La2CuO4+δ, in the high-pressure, oxygen-annealed samples. For samples analyzed at room temperature, x-ray diffraction measurements show that beyond δ ≍ 0.10–0.13, additional oxygen is accommodated in a perovskite-like LaCuO3−α phase. An analysis of the thermochemical measurements indicates that the nature of holes in La2CuO4+δ could change in the range of δ ≍ 0.03–0.06.16,17 It is further suggested that the observed change in the thermochemical behavior in the range of δ ≍ 0.03–0.06 could be the driving influence behind the spinodal decomposition of La2CuO4+δ at low temperatures (Dabrowski et al.10).

Reactive liquid phase sintering of the YBCO films prepared from carboxylate solution precursors was investigated. A liquid phase was formed by the BaO—CuO binary compound at 620 °C, which facilitated the crystallization and growth of the YBCO grains. Strong capillary forces associated with the liquid phase sintering resulted in a dense, highly oriented microstructure. The YBCO films processed by this reactive liquid phase process showed Tc(zero) = 90.2 K and Jc = 1.3 × 105 A/cm2 at 77 K. The (006) rocking curve measurement indicated excellent grain orientation with a FWHM better than 0.2°. A secondary ion mass spectroscopy (SIMS) study showed uniform film composition, and the film/substrate interaction zone was limited to ≈0.1 μm. Average film roughness was about 32 nm.

A new potassium phosphatoantimonate with a composition of 4K2O · 4Sb2O5 · P2O5 · 8H2O, which crystallizes in a monoclinic system with a = 23.952 Å, b = 9.515 Å, c = 8.193 Å, and β = 124.77, was hydrothermally synthesized and characterized by powder x-ray diffraction, chemical composition analysis, x-ray photoelectron spectroscopy, and 31P MAS-NMR techniques. The potassium ion can be exchanged by other monovalent ions.

BaTiO3 doped 90V2O5−10Bi2O3 (VB) oxide glasses show a larger dielectric constant (102-104) compared to that of the base glass VB (∼102). The VB glass with 15 wt.% BaTiO3 shows the largest dielectric constant, and all the glasses show a Debye-type dielectric relaxation behavior. The increase in dielectric constant appears to be mainly due to the formation of microcrystalline clusters of BaTiO3 (1.8–8 μm, depending on the BaTiO3 concentration present in the base glass). Other than the dilution effect with BaTiO3, the glass-former oxide Bi2O3 also influences the dielectric behavior of BaTiO3 doped VB glasses.

The mullite phase has been synthesized by subjecting a suitably chosen precursor gel to different pressure and temperature conditions. At ambient pressure mullite phase grows at a temperature of 1400 °C when the gel is heated for 2 h. At a pressure of 24 bar, on the other hand, similar growth occurs at a temperature of 750 °C for 5 min.

Mo(NBut)2(NHBu1)2 is used as a single-source precursor to deposit thin films of cubic phase molybdenum carbonitride, MoCxNy (x: 0.2-0.55, y: 0.1-0.47), by chemical vapor deposition on silicon substrates. In general, the C/Mo ratios increased from 0.2 to 0.55 and the N/Mo ratios decreased from 0.47 to 0.1 with increasing the temperature of deposition from 773 to 923 K. Based on the elemental composition and the composition of the gas phase products, it is proposed that the carbon atoms were incorporated through β-methyl activation of the ligands.

Stable cubic ZrO2 up to a temperature of 1173 K has been synthesized by a chemical precipitation technique. Such a stability appears to be driven by particle size. The critical value below which cubic ZrO2 has been found to be stable is 17 nm. The x-ray diffraction pattern of such ultrafine cubic particles is similar to that obtained by stabilization of ZrO2 by the addition of 20 mole % CaO.

The variation of grain morphology in silver-doped YBa2Cu3O7−x was investigated as a function of sintering temperature, atmosphere, and amount of Ag addition. In the presence of the liquid phase formed at 925 °C for undoped samples, and at 910 °C for silver-doped samples, the grain shape and size changed drastically from small and nearly equiaxed to large and elongated. The anisotropy in the grain shape was sensitive to both the silver content and the atmosphere. On the other hand, while the grain size was generally insensitive to the atmosphere, it decreased as the silver content increased. The silver phase, if sufficiently large, would block the grain growth in the matrix. The amount of silver for effective blocking was predicted from a microstructural model, and the prediction was in agreement with experimental results.

High energy ball milling has been used to produce nanocrystalline Y1Ba2Cu3O7-δ powders. These powders are being used as starting materials for manufacturing superconducting textured wires by a solid state recrystallization process. Magnetic and microstructural characterizations were performed as a function of milling time. The milling reduces the average crystal size and creates low and high-angle grain boundaries which increase the granularity of the superconductor. As a result, the long-range order on the oxygen sublattice and on the yttrium and barium sites is destroyed. A transition from orthorhombic to tetragonal and finally to a cubic metastable phase is observed. Total loss of superconductivity occurs after about 1 h of milling. Prior to this time, superconductivity can partially be restored by room-temperature aging. High-temperature heat treatment of the nanocrystalline phase produces a tetragonal structure with c = 3a.

Recently we have found a very effective method for controlling the orientation of YBCO films by metal-organic chemical vapor deposition (MOCVD) using uv laser irradiation during deposition onto a MgO(100) substrate. The irradiated part was strongly a-axis-oriented normal to the surface of the substrate for films prepared at 650-700 °C, whereas the unirradiated parts showed c-axis or (110) orientation. This phenomenon occurs not only on MgO(100) substrates but also on other substrates. We obtained a Tc above 81 K on the a-axis oriented part. The critical current density was over 105 A/cm2 at 4.2 K and O T. The surface morphology depends on the laser power density and the repetition rate. A high degree of the a-axis orientation is obtained only by using uv light during deposition of YBCO film. IR or a visible laser causes only surface melting and the destruction of film orientation. We propose that the nuclei for a-axis orientation are formed by the aggregation of Ba caused by uv laser irradiation near the film surface.

We describe a method for directly determining the strain state of passivated metal lines. Synchrotron radiation in the grazing incidence geometry is used to directly measure the in-plane interplanar spacing along the length and width of the lines, while the strain normal to the surface of the line is measured using conventional diffraction methods. The entire strain state is thereby defined. Previous work has measured out-of-plane reflections, fit them to a straight line as a trigonometric function of the angle of orientation, and extrapolated to determine the principal strains. The equivalence of the two x-ray methods on the same sample is demonstrated at room temperature before and after thermal cycling. For short time strain relaxation experiments during thermal cycling, measurement of the three principal strains leads to the direct calculation of the stress relaxation. We apply the strain determination technique to Al-0.5% Cu lines passivated with Si3N4 as the lines are thermally cycled from room temperature to 450 °C and back. The strain state, stress state, and strain relaxation of the lines are calculated at several temperatures during thermal cycling.

The a-axis oriented YBa2Cu3Ox (YBCO) films were epitaxially grown on (100) SrTiO3 substrate by dc-100 MHz hybrid plasma sputtering. The films prepared at different temperatures with and without in situ annealing had different superconductivity, which was improved with the degradation of the crystallinity of the films. The Raman spectra for the films were very similar to each other and to that expected for YBa2Cu3O7, in spite of the different superconductivity. This indicates the importance of the symmetry of the Cu–O chains rather than the oxygen content for the superconductivity. In Rutherford backscattering measurements using a 3.05 MeV He2+ ion beam, an increase of dechanneling due to the barium atoms along the film depth was clearly observed only for the most improved superconducting film. This result suggests that the relief of the strain contained in the film is also important for improving the superconductivity in the case of a-axis oriented YBCO films.

Pyrochlore-type Pb2FeWO6.5 is difficult to be sintered without applied pressure at temperatures lower than its decomposition temperature. Through hot pressing or hot isostatic pressing processes, densification of specimens is greatly enhanced; moreover, grain growth during sintering is effectively suppressed. Densified Pb2FeWO6.5 exhibits paraelectric characteristic from −135°to −2 °C with low dielectric constants and low dissipation factors. The dielectric constants show rather weak dependence of temperature and frequency.

Systematic studies have been performed on 1000 Å YBa2Cu3O7−δ films produced by the BaF2 process and annealed in an oxygen partial pressure (Po2) range from 740 Torr to 10 mTorr as well as a temperature range from 600 to 1050 °C. The results show that while high quality films can be annealed in a wide range of oxygen partial pressure, they have different characteristics. In general, crystalline quality and Tc are optimized at high Po2 and high annealing temperature, while strong flux pinning and low normal state resistivity are achieved at lower values of both variables. Under optimized low Po2 conditions, an ion channeling Xmin of 6% is obtained on films as thick as 5000 Å. This study will serve as a useful guide to tailoring film properties to the application at hand.