AlN powders (particle size = 0.44 ± 0.08 μm) containing no deliberate sintering additives were consolidated to near theoretical density in 5 min at 2003 K (1730 °C) using a Plasma Activated Sintering (PAS) process. PAS is a novel consolidation method that combines a very short time at high temperature with pressure application in a plasma environment. The in situ cleaning ability of powder particle during plasma activated densification leads to enhanced particle sinterability. The densities of undoped AlN specimens that were PAS consolidated at 2003 K for 5 min under 50 MPa pressure ranged from 97.5 to 99.3% of theoretical. The initial submicron particle size of AlN powders was retained in the final microstructure that consisted of polycrystalline grains with an average size of ≍0.77 ± 0.1 μm.

Single crystal films of C60 of different thickness values have been deposited on mica substrates by resistance evaporation. Electron diffraction and high resolution microscopy have been used to assess the orientational ordering and the nature of the defects present in these face-centered cubic films which exhibit a 〈111〉 direction normal to the film surface.

Atomic hydrogen obtained from dissociative chemisorption of molecular H2 on Pt particles deposited on the surface of YBa2Cu3O7 reacts with the oxide in producing O vacancies and intercalating H at 82 °C under a H2 pressure of about 400 Torr. An induction period which extends over 1 h is observed as long as the concentration in O vacancies is below 0.1. Above this approximate limit the reaction proceeds quickly until about 1 mol H2 has been consumed. It then slows down progressively, but it is not completed even after 27 h of reaction and ∼1.4 H2 consumed, under these experimental conditions. The enthalpy for the creation of the O vacancy is 143 kcal/g mol O, while the H intercalation enthalpy is −57.5 kcal/g mol H. It appears that the reaction of molecular H2 over YBa2Cu3O7 not coated with Pt proceeds similarly, but the rate is nearly one order of magnitude slower, under identical conditions. The stoichiometry of the reaction agrees with the earlier suggestion that O1 is a labile oxygen which can be replaced by intercalated H. This site and the interstitial vacant sites in the copper chains square plane would be the first ones to be occupied by intercalated H.

Phase pure YBa2Cu3O7 high transition temperature superconductor powders were synthesized by a new precursor route. This new synthesis procedure is easy, leads to an atomic mixture of the relevant constituents, and is readily adaptable to many other systems or to the doping of existing systems. A gel of yttrium, barium, and copper salts was prepared using organic gelling agents. The gel was then dried and ground, leaving the xerogel precursor. These xerogels are perfectly stable even under high humidity atmospheric conditions and show an amorphous structure when characterized by x-ray diffraction, which is consistent with the existence of an atomic mixture of the three relevant metal salts. The organic gelling agent was selected after optimization studies focused on such issues as ash residue after calcination, solubility, and chemical interference with the metal salts. From a great variety of these gelling agents (agar, xanthan gum, gelatin, alginates, and others), gelatin was chosen as the ideal gelling agent for this specific application. The final product characterization shows very unexpected results. The crystalline phase purity of the YBa2Cu3O7 superconducting phase was about 99%, with no traces of barium carbonate, as expected from pseudo-organic precursors (xerogels). The product shows superconducting properties even before oxygen anneal (Tc ≍ 70 K), and after oxygen annealing of the powders the transition temperature was found to be 91 K, showing a linear behavior of the resistivity versus temperature before the drop at Tc, extrapolating to zero at 0 K. The particle size of these powders is smaller than 1 μm, as shown by SEM.

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 a-axis YBa2Cu3O7–δ thin films have been grown on SrTiO3 (100) by on-axis 94.92 MHz magnetron sputtering using the YBa2Cu5Ox target at a self-bias voltage of −50 V and YBa3Cu7Ox target at a cathode voltage of −100 V adjusted by externally applying a negative dc voltage. Good crystalline quality of the films sputtered at −50 V was confirmed from a full width at half maximum, δω, of 0.04° through the (100) peak by x-ray diffraction and a minimum yield, Xmin, of 4.8% by Rutherford backscattering channeling. Those films, however, have not shown superconductivity. On the other hand, the films sputtered at −100 V were characterized by a δω of 0.12° and a Xmin of 4.3%. Superconductivity occurs in the films only by shifting a self-bias voltage from −50 V on the YBa2Cu5Ox target to −100 V on the YBa3Cu7Ox target. The zero resistance temperature is 33 K at most.

The filaments have been prepared by dry spinning through a homogeneous aqueous solution containing mixed acetates of Y, Ba, and Cu, polyvinyl alcohol, and organic acids. After spinning, the filament was sintered or partially melted to generate the superconducting phase. Magnetization properties of the filaments are examined. Since solution spinning introduces a fine flux pinning center into the superconducting phase, such as at elemental level, a significantly improved Jc value estimated from the magnetization curves and field dependence of the Jc have been achieved in the solution-spun filament. The phase decomposition from the 124 phase to the 123 phase and partial melting result in an enhancement of flux pinning.

In the preparation of YBa2Cu3Oy (Y-123) superconductor, the coprecipitation method was frequently used in various solution systems due to advantages such as good homogeneity, low reaction temperature, fine and uniform particle size, easy scale-up, and economical concerns. In this paper, a detailed study of different competitive reactions such as dissociation, precipitation, complex formation, and association involving metal ions, oxalate ion, and diethylamine species is performed. The study aids in understanding the precipitation and yields an optimal coprecipitation condition for the title system. A series of experiments are also conducted which confirm that the as-derived optimal condition may be extensively applied to other systems.

Three processing routes that generate uniaxial alignment but otherwise yield very different microstructure and critical current are compared. Fine grain size and c-axis alignment are obtained in magnetically aligned ceramics, pyrolyzed thick films, and in situ deposited thin films. The dense, well-aligned microstructure of the in situ process produces the highest zero field critical current Jc > 104 A/cm2 at 77 K. However, the critical current is suppressed in low magnetic field, suggesting that uniaxial alignment is not sufficient to avoid Josephson-type intergranular coupling. Above 1 T, the critical current of the aligned ceramic dominates in spite of its less ideal microstructure. The critical current in this high field region is one to two orders of magnitude greater than that of nonaligned material. This result implies the existence of a 3-d percolative network of strong links.

Mechanochemical effects on the synthesis and pulverization process of the Ba2YCu3O7−y superconductor (abbreviated to BYCO) and BYCO–Ag composite were examined. Grinding of the precursor of BYCO promoted the homogeneous distribution of each element and subsequently the crystallinity of the precursors was decreased. The sintered body obtained by using the ground and calcined powder had complicated crystal phases consisting of the BYCO phase with secondary phases and resulted in the impairment of the superconducting transport current property. Grinding of crystallized BYCO powder decreased its grain size and crystallinity; the crystallinity was recovered by annealing. On the other hand, grinding contributed to the synthesis of the BYCO–Ag superconducting composite by minimizing the particle sizes and mixing of components. The BYCO–Ag composite so obtained displayed improvement of superconducting properties.

The morphology of typical CVD diamond thin films has been shown to be controlled by the concentration of methane during deposition. For example, for CH4 concentrations c < 0.4% the (111) faces dominate, while at 0.4% < c < 1.2% (100) faces dominate. Here we showed that the (100) oriented diamond films can be grown on top of the microcrystalline ball-like particles under suitable conditions. These (100) oriented diamond films are grown under the condition of 1.5% methane in hydrogen, substrate temperature of 680 °C–750 °C, and pressure of 30–80 Torr. The bombardment of the diamond thin films by ions in the plasma is believed to be an important factor for the formation of (100) oriented films on top of the ball-like particles. SEM, Raman, and x-ray techniques were used to characterize the deposited (100) oriented diamond thin films.

The structure of buried oxide layers formed by low-dose 16O+ implantation of 0.4 and 0.7 × 1018 cm−2 at 180 keV and by subsequent annealing in the temperature range of 1150 to 1350 °C has been investigated using cross-sectional transmission electron microscopy (XTEM). At a dose of 0.4 × 1018 cm−2, an 80-nm continuous uniform buried oxide layer having a breakdown voltage of approximately 40 V is formed after annealing at 1350 °C. At a dose of 0.7 × 1018 cm−2, multiple buried oxide layers having Si islands between them are formed at an anneal temperature of 1150 °C. The number of multiple layers is reduced as the annealing temperature increases, but the Si islands do not dissolve even after annealing at 1350 °C. The existence of the Si islands causes the breakdown voltage to fall to 0 V despite the higher dose.

Cracks of up to 40 μm which are either transgranular cleavage or very low energy “ductile” cracks have been introduced into large-grained fcc Ni. The mechanism for introducing this brittle fracture was dynamic indentation. Optical and scanning electron microscopy together with use of selected area channeling patterns were used to confirm that the fracture process is transgranular. The results qualitatively support the hypothesis that dynamic cracks originating in a brittle film can propagate relatively large distances into a ductile face-centered-cubic substrate by a rapid, low energy process.

The precise structural characteristics of the amorphous solids that are generated during the dehydration of crystalline MgHPO4 · 3H2O (newberyite) are reported. The results show that a dramatic change in the distribution of phosphate anions (i.e., chains of corner-linked PO4 tetrahedra) occurs during the process of dehydration and that anions up to 13 PO4 tetrahedra in length are formed. The distribution of phosphate anions formed at intermediate stages of the dehydration process was found to be in quantitative agreement with the theory of Parks and Van Wazer.

The initiation and growth of α–Al2O3/metal composites by the directed oxidation of molten Al–Mg, Al–Si, and Al–Mg–Si alloys at 1373 and 1523 K were investigated. Spontaneous initiation and growth occurred only on the ternary Al–Mg–Si alloy. Growth also occurred on the Al-Mg binary alloy, but in this case initiation required the mechanical disruption of the protective oxide formed during initial heating to the growth temperature. In addition, mechanical disruption of the protective oxide scale on the Al–Mg–Si alloy enhanced growth initiation. Growth on the Al–Si alloy could not be induced under any conditions. From these observations it is concluded that, in the directed oxidation of Al–Mg–Si alloys, Mg is essential to the accelerated oxidation reaction, while Si appears to play a role in promoting the breakdown of the protective oxide layers. The most uniform initiation and growth results were obtained by providing a thin layer of SiO2 particles at the initial growth surface of the alloy.

High-angle grain boundaries in YBa2Cu3O7−δ thin films are of technological interest because of the weak coupling observed between the grains; however, not all high-angle grain boundaries show this weak-link behavior. The microstructure of both these boundaries is not understood, nor is the reason for the differing electrical transport properties. High-angle grain boundaries in YBa2Cu3O7−δ thin films on MgO, where the angular misorientation between the grains is ∼45°, have been examined using high-resolution electron microscopy. The results show that the boundary structure can appear quite different even when the angular misorientation between the two grains is the same. The stability of the grain boundaries under the electron irradiation in the electron microscope was found to be a function of the accelerating voltage—400 kV leads to rapid disordering of the boundary region.

Superconducting materials in the Bi–(Pb)–Sr–Ca–Cu–O system have been synthesized by sol-gel processing from nitrates by complexation with citric acid. The gelation process and the microstructures of the gels obtained have been studied through titration and SEM observation. Their phase transformations and microstructure development, during heat treatment, have also been investigated. The critical temperature Tc of superconductors by this sol-gel processing can reach above 100 K.

Observations of the Bi–O surface of superconductive Bi2212 single crystals were carried out using an ultrahigh-vacuum scanning tunneling microscope (UHV-STM). In the atomic resolution images, surface corrugations, which correspond to the superstructure of the Bi–O surface in addition to Bi atom deficiencies, were observed. There were hollow lines along the ridges of the corrugations, which may be due to missing atom rows.

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.

The effect of G/R (temperature gradient, G; growth rate, R) on the crystal alignment and the crystallization mechanism of YBa2Cu3Oy (123) from the partially melting state [in which Y2BaCuO5 (211) and liquid coexist in equilibrium] grown by the horizontal Bridgman method was investigated. Highly aligned 123 crystals containing fine 211 particles were obtained at high G/R ratios. The limit of G/R for continuous growth, necessary for obtaining textured structure, was confirmed to exist between 301 and 482°Ch/cm2. A high critical current density (Jc) of 1.9 × 104 A/cm2 (77 K, 1 T) was measured for a sample grown at the high G/R condition of 482°Ch/cm2, and the 123 grains grown under a condition of G/R lower than the lower limit became coarser with decreasing GR (cooling rate). Entrapment of the 211 particles in the growing 123 crystals occurs after significant coarsening of the particles in the liquid since observed radii of the 211 particles were independent of the distance from the solid/liquid interface in the 123 crystals.