We measured the elastic constants of polycrystalline Y1Ba2Cu3Ox with eleven oxygen contents varying from 6.2 to 6.9. Reported properties include sound velocities; bulk, shear, Young's moduli; Poisson ratio; Debye temperature. After correction to the void-free state, the measurements fail to show a systematic dependence on oxygen content. Focusing on the bulk modulus, all measurements fall below an ionic-crystal model prediction, by 5–50%. We attribute this macroscopic softness to either microcracks or weak grain-boundary mechanical linkages. For the case x = 6.9, we suggest a set of intrinsic elastic constants.

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.

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.

High temperature reaction calorimetry using molten lead borate as a solvent is used to study the thermochemistry of phases in the Y2O3–BaO–Cu–O system. Enthalpies of formation of YBa2Cu3Ox (6 < x < 7), YBa2Cu4O8, Y2BaCuO5, Y2Cu2O5, and BaCuO2.01 phases have been determined. The thermodynamic relationships among these phases at room temperature have been assessed. The results show that the 123 phase is not thermodynamically stable with respect to assemblages containing combinations of Y2BaCuO5, Y2Cu2O5, BaCuO2, Y2O3, and CuO. The fully oxidized 123 phase is not stable with respect to the 124 and the above assemblages. Reactions at room temperature are shown as follows: YBa2Cu3O7 (s) + CuO (s) → YBa2Cu4O8 (s); δH = −31.9 ± 22.3 kJ mol−1 and YBa2Cu3O6.76 (s) → ½YBa2Cu4O8 (s) + ¼Y2BaCuO5 (s) + ¾BaCuO2.01 (s); δH = −78.9 ± 21.0 kJ mol−1.

The interfacial reactions between the Y1Ba2Cu3O7−x (123) compound and a Ag70Pd30 alloy have been studied for several heat treatments below and above the melting point of the superconductor. Scanning and transmission electron microscopy, energy dispersive x-ray analysis, Auger spectroscopy, and x-ray diffraction have been used to characterize the reaction products. For the heat treatments below the melting point of the superconductor (950 °C), the Ba and Cu of the 123 compound migrate to the interface and react with the Pd to form a body-centered cubic phase Ba(Pd, Cu)O2. This structure is formed by substitution of Cu by Pd on the Cu+2 sites of the BaCuO2 structure (Im3m space group). CuO is also found in some areas as a product of the reaction. For the thermal treatments above the melting point of the superconductor, the reaction products are the same but, in this case, a large number of Y2BaCuO5 precipitates are found in the bulk of the superconductor near the interface. Pure Ag particles have also been observed in the 123 compound at distances relatively far from the interface.

YBa2Cu3O7−x–Ag and YBa2Cu3O7−x–SiO2 composite superconductors were prepared by the spray drying method. The composite powder was prepared by calcination of the precursor powder, which was synthesized by spray drying the oxalate slurries and dissolved components. Fine Ag, Ba2SiO4, and other phases were distributed in composite sintered bodies, with the added Ag or SiO2 showing enhanced magnetic properties.

Phase compositions and microstructures of melt processed 2212 were studied. 2212 starting powder was cooled from temperatures between 910 °C and 1100 °C in air at rates ranging from 350 K/min to 0.083 K/min. The solidification sequence was established for all cooling rates. Under all conditions the Bi-free (Sr, Ca)CuO2 (01x1) is the primary phase. The one-layer solid solution 11905 nucleates on this phase. The residual liquid solidifies to a glassy state, decomposes into the eutectic of Cu2O and Bi2Sr2.1Ca0.9Ox, or reacts with the primary phase and the 11905 forming 2212 at high, intermediate, or low cooling rates, respectively. Post solidification heat treatment at 850 °C in air leads to partial remelting. The Cu-rich liquid reacts with 11905 and 01x1 forming 2212. Subsequent solid/solid reactions lead to a high volume fraction of 2212 with almost ideal 2 : 2 : 1 : 2 stoichiometry.

Bi2Sr2CaCu2O8+x films were prepared by mixing 2-ethylhexanoate precursors with heptafluorobutyric acid and annealing at 820 °C in dry ambient. The films underwent substantial mass transport and exhibited abnormal grain growth, indicating that some liquid phases might be involved in the process. It was found that the high atomic mobilities during annealing significantly improved in-plane orientations and consequently increased critical current densities.

Nanophase TiAl, with grain sizes in the range of 10–20 nm, was synthesized by magnetron sputtering in an inert gas atmosphere and consolidated, in situ, under vacuum. The properties of the powders and sintered compacts were studied by transmission electron microscopy, scanning electron microscopy, calorimetry, Rutherford backscattering, and x-ray diffraction. Samples compacted at 1.0 GPa at room temperature had a large fraction of amorphous phase, while samples compacted at the same pressure and 250 °C were predominantly the equilibrium γ phase. An enthalpy change of 22 kJ/g-atom was measured during a DSC scan over the temperature range 125–450 °C, which is approximately the range over which crystallization occurs. Nearly full density could be achieved by sintering at 450 °C without significant, concomitant grain growth. The Vickers microhardness of these samples at room temperature and at −30 °C revealed an inverse Hall–Petch relationship at small grain sizes, 10–30 nm, and the usual Hall–Petch behavior at larger grain sizes. A small component of indentation creep was also observed. The maximum hardness is 4 times larger than that of a cast TiAl specimen of the same composition. The Vickers hardness was also observed to decrease rapidly with temperature above 200 °C.

X-ray diffraction patterns obtained during the grinding of Ni3Ge and Ni3Al alloys which at equilibrium exhibit the L12 ordered fcc structures show the emergence of a nanocrystalline structure and transformation to the disordered fcc form but little amorphization. Furthermore, the non-L12 Al2Pt alloy which also has a more strongly negative heat of mixing is easier to amorphize than the Ni3Ge and Ni3Al with L12 superstructure. This is in contrast to the Zr3Al compound (also L12-type) for which a short milling time is sufficient for obtaining complete amorphization. Variations in the aptitudes toward amorphization of the three L12-type alloys under ball-milling conditions are attributed in part to the differences in the lattice stability terms of their disordered fcc phases.

We have studied the effects of temperature (10 ≤ T ≤ 295 K) and pressure (0 ≤ p ≤ 0.8 GPa) on the state of intercalate layer crystallization in SbCl5 graphite intercalation compounds of stages 2, 4, and 8. At room temperature (RT), the intercalate layer may in some second stage compounds be fully crystallized and lowering the temperature creates no further modifications. In all other cases, i.e., those in which the intercalate layer has only partial crystallization at RT, lowering T leads to the formation of new in-plane unit cells, the final state depending on the kinetics. Applying pressure to above 0.3–0.5 GPa results in crystallization in all cases, different from that induced simply by lowering of the temperature. We discuss the unit cells observed and the relationships they bear to each other in the light of other works on similar compounds.

We present experimental data for the c-axis resistivity ρc of stage s = 2, 3, 4, 5, and 8, SbCl5 intercalated graphite, over the temperature range 40 to 300 K and the pressure range 0 to 0.8 GPa (0–8 kbar). For most specimens studied, resistance anomalies are observed below 230 K at atmospheric pressure and at pressures up to 0.5 GPa at 293 K. These anomalies are explained in terms of structural changes from a disordered or partly crystallized in-plane intercalate structure at atmospheric pressure and T > 230 K to an almost completely crystallized structure below this temperature, or at elevated pressures, as discussed in a companion paper. In the crystallized phases ρc is approximately linear in T except for stage 8, for which a nonlinear behavior, with a negative temperature coefficient of resistivity below 200 K, is observed. The results are compared with previously available literature data, and the p-T phase diagram is briefly discussed.

Flat, hexagonally shaped diamond platelets were observed during the initial stage of microwave plasma assisted deposition of diamond. The platelets are approximately 2.5 μm in linear dimension and are oriented with their large six-sided faces parallel to the silicon substrate. A re-entrant groove, running parallel to the large six-sided face, is present in the small side faces of the platelets. Larger diamond crystals, with a fully developed three-dimensional morphology, all have re-entrant grooves in other directions. The observations support the hypothesis that the growth rate of {111} faceted diamond crystals is greatly enhanced by the presence of microtwins (multiple stacking errors), which give rise to re-entrant corners where they intersect the crystal surface. Fully developed {111} faceting and a strong influence of re-entrant corners is expected when the average lifetime of a carbon atom bonded once to the surface is much less than the average time between addition of adatoms at adjacent surface sites.

A simple hot-pressing procedure for fabricating composites of diamond particulates in an alumina matrix at moderate applied pressures is described. Dense composites with up to 33 vol. % diamond particles are made by pressure-sintering at applied stress of 35 MPa in vacuum atmosphere. Preliminary wear tests of these composites on magnetic thin-film rigid disks show a low friction comparable to that of single crystalline diamond. Diamond/alumina composites can be an economical alternative to diamond or diamond coated materials for abrasion resistant applications.

Tensile strength and Young's modulus were determined for vapor-grown carbon fibers (VGCF's) prepared from benzene in Linz–Donawitz converter gas (LDG) by the floating catalyst method. The tensile strength decreased with increasing diameter and volume and depended strongly on whether the fiber was straight or crooked. The average tensile strength of straight fibers was 2.05 GPa, while that of crooked fibers was 1.09 GPa. The latter broke at bends in the fiber where they acted as defects. The average Young's modulus of straight fibers was 163 GPa, while that of crooked fibers was a little higher at 197 GPa. VGCF's prepared in LDG appeared to have comparable mechanical properties to those grown in hydrogen.

Deposition rates are predicted in a cylindrical upflow reactor designed for chemical vapor deposition (CVD) on monofilaments. Deposition of silicon from silane in a hydrogen carrier gas is chosen as a relevant example. The effects of gas and surface chemistry are studied in a two-dimensional axisymmetric flow field for this chemically well-studied system. Model predictions are compared to experimental CVD rate measurements. The differences in some physical and chemical phenomena between such small diameter (∼150 μm) fiber substrates and other typical CVD substrates are highlighted. The influence of the Soret mass transport mechanism is determined to be extraordinarily significant. The difficulties associated with the accurate measurement and control of the fiber temperature are discussed. Model prediction sensitivities are investigated with respect to fiber temperatures, fiber radii, Soret transport, and chemical kinetic parameters. The implications of the predicted instantaneous rates are discussed relative to the desired fiber properties for both batch and continuous processes.

Dislocation accumulation in gallium-arsenide film, which is deposited on silicon substrate and cooled down from the deposition to room temperature, is examined by crystal plasticity simulation. A new approach to suppression of dislocation accumulation is proposed such that selective growth of the film and partial doping of impurities into it are combined. The results show the possibility to localize the plastic deformation near the film/substrate interface and to keep the surface region of the film almost dislocation-free. Geometry of the selectively grown film and a strategy for partial doping of impurities, which suppresses the dislocation accumulation in the surface region of the film, are considered.

Material properties are greatly dependent upon the structure of the material. This paper, the first of three parts, discusses how composition influences the crystallographic structure and microstructure of lead lanthanum titanate (PLT) thin films grown by the multi-ion-beam reactive sputtering (MIBERS) technique. A transmission electron microscopy (TEM) study detailing the relationship between crystallographic texturing and microstructure development will be presented in a second paper. The dependence of the ferroelectric properties on observed crystallographic structure and microstructure is presented in the third paper of this series. As-deposited PLT microstructures coincide with the structure zone model (SZM) which has been developed to describe the microstructure of thin films deposited by physical vapor deposition. The as-deposited PLT structures are altered during post-deposition annealing as a result of crystallization and PbO evaporation. Amorphous films with more than 10 mole % excess PbO become polycrystalline with porous microstructures after annealing. When there is less PbO in the as-deposited film, 〈100〉 texture and dense structures are observed. Porosity results from PbO evaporation, and 〈100〉 texture is inhibited by excess PbO.

Two equations for determining the hardness of thin films from depth-sensing indentation data are examined. The first equation is based on an empirical fit of hardness versus indenter displacement data obtained from finite element calculations on a variety of hypothetical films. The second equation is based on a model which assumes that measured hardness is determined by the weighted average of the volume of plastically deformed material in the coating and that in the substrate. The equations are evaluated by fitting the predicted hardness versus contact depth to data obtained from titanium coatings on a sapphire substrate. Only the volume fractions model allows the data to be fitted with a single adjustable parameter, the film hardness; the finite element equation requires two thickness-dependent parameters to obtain acceptable fits. It is argued that the difficulty in applying the finite element model lies in the use of an unrealistic area function for the indenter. For real indenters, which have finite radii, the area function must appear explicitly in the final equation. This is difficult to do with the finite element approach, but is naturally incorporated into the volume fractions equation. Finally, using the volume fractions approach the hardnesses of the titanium films are found to be relatively insensitive to film thickness. Thus, the apparent increase in hardness with decreasing film thickness for the titanium films is most likely due to increased interactions between the film and substrate for the thinner films rather than to a change in the basic structure of the titanium films.

Phase transformation and preferred orientation in ZrO2 thin films, deposited on Si(111) and Si(100) substrates, and prepared by heat treatment from carboxylate solution precursors were investigated. The deposited films were amorphous below 450 °C, transforming gradually to the tetragonal and monoclinic phases on heating. The monoclinic phase developed from the tetragonal phase displacively, and exhibited a strong (111) preferred orientation at temperature as low as 550 °C. The degree of preferred orientation and the tetragonal-to-monoclinic phase transformation were controlled by heating rate, soak temperature, and time. Interfacial diffusion into the film from the Si substrate was negligible at 700 °C and became significant only at 900 °C, but for films thicker than 0.5 μm, overall preferred orientation exceeded 90%.