The decagonal phase was studied by transmission and scanning electron microscopy in an Al62Cu24Co14 alloy annealed at 550–850 °C. The electron diffraction patterns of the decagonal phase exhibited weak quasiperiodic odd-n reflections in the [1-2100] zone axis corresponding to the equilibrated structure. The relative intensities of these reflections were significantly lower in the Al62Cu24Co14 than in the Al68Cu11Co21 decagonal phase. Diffuse scattering observed previously at the same positions can be related to a nonequilibrium state of the decagonal phase.

Solid solutions of aluminum nitride (AlN) and silicon carbide (SiC), the only intermediate phases in their respective binary systems, have been grown at 1050 °C on α(6H)-SiC(0001) substrates cut 3–4° off-axis toward [11$\overline 1$0] using plasma-assisted, gas-source molecular beam epitaxy. A film having the approximate composition of (AlN)0.3(SiC)0.7, as determined by Auger spectrometry, was selected for additional study and is the focus of this note. High resolution transmission electron microscopy (HRTEM) revealed that the film was monocrystalline with the wurtzite (2H) crystal structure.

Highly oriented SnO2 thin films have been grown successfully from tetra-n-butyltin on heated glass substrates by a pneumatic spraying system. The effects of film growth rate and substrate temperature on the microstructures of the films were investigated by x-ray diffraction and scanning electron microscopy. The SnO2 films of preferentially oriented (110) crystal plane were grown under the optimum growth conditions.

The heat capacity and the enthalpy associated with the reported oxygen vacancy order-disorder transition in Ba2In2O5 were measured by high temperature step scanning calorimetry. The transition temperature is 1205 ± 2 K. The transition appears first order or nearly so. The enthalpy and entropy of transition are 1.3 kJ/mol and 1.1 J/mol K, respectively. The latter is only 4.8% of the configurational entropy, arising from mixing one vacancy and five oxygens per formula unit, 22.5 J/mol K. This suggests that the transition involves only a small fraction of the oxygen vacancies and implies extensive short-range order, SRO, in the high temperature phase.

Soluble metal oxo alkoxide precursors are useful for the production of homogeneous, micron-sized YBa2Cu3O7−x powders and the fabrication of superconducting YBa2Cu3O7−x films on large area and nonplanar substrates. This paper describes the synthesis and chemistry of a series of soluble metal oxo alkoxide precursors for the YBa2Cu3O7−x superconducting material and the effect of the thermal processing conditions on the formation of the superconducting phase. We have found that the direct conversion of the metal oxo alkoxide precursors to an amorphous or crystalline YBa2Cu3O6.5 phase without the intermediate formation of the individual metal oxides or carbonates allows the formation of the superconducting phase at temperatures as low as 720 °C. The prevention of the intermediate formation of the metal oxide and carbonate phases is achieved by the controlled thermolysis of the metal oxo alkoxide precursors in an inert atmosphere. The precursors have potential use in the low-temperature deposition of films on large area or nonplanar surfaces and for the production of homogeneous powders.

The photoelectric work function of samples of Y1Ba2Cu3O7−δ of approximately 40 μm diameter was measured under ambient temperature and atmosphere in an electrodynamic balance. The measured values had an average of 4.98 eV and a standard deviation of 0.24 eV. The minimum value was 4.46 eV and the maximum was 5.52 eV.

This investigation focused on the effects of TiO2 additions (2.5–5 mol%) incorporated via sol-gel coating of powders on sintering behavior, microstructure development, electrical resistivity, and magnetic susceptibility of YBa2Cu3O7−x. Specimens were sintered at ≤ 960 °C for 6 h in all cases. TEM analysis indicated the sol-gel coating to be uniformly distributed around each particle and of thickness ∼ 20 to 40 nm. The addition of TiO2 was seen to reduce the sintering temperature by up to ∼ 200 °C, indicating the formation of a liquidus phase below that normally reported for YBa2Cu3O7-x. Grain growth and grain anisotropy behavior were influenced by TiO2 addition. A maximum in density, grain size, and anisotropy was achieved with 2.5 mol% addition sintered at 930 °C. TiO2 addition was shown to result in the formation of greater amounts of secondary phases such as Y2BaCuO2, and BaCuO2, particularly at higher TiO2 levels and sintering temperatures. The use of TiO2 additions also altered the magnetic susceptibility with the optimum response occurring for samples with 2.5 mol% TiO2 addition when sintered at 930 °C.

In order to understand the effects of the thermodynamic stability on superconductivity, the thermodynamic stability of the Bi2Sr2CaCu2-xLixOy system and the Bi2Sr2YCu2-xLixOy system was studied. It is found that the broad ranges (0 ≤ x ≤ 0.6) of solid solution may be thermodynamically stable at high temperatures for the Bi2Sr2CaCu2-xLixOy), system and the Bi2Sr2YCu2-xLixOy), system. At equilibrium at low temperatures, however, solid solubility is eliminated, and only the end member compounds and possibly intermediate compounds of fixed composition remain for 0.3 ≤ x ≤ 0.6. It suggests that Li can destroy the thermodynamic stability. Superconductivity is improved by Li-doping, which may be related to the thermodynamic instability.

Simulations of arrays of resistively shunted Josephson junctions containing a crack of uncoupled junctions indicate that the crack can distort the supercurrent flow and provide a nucleation site at the crack tip for the formation of superconducting vortices at applied currents below the critical current of the homogeneous material. An analogy is established between the supercurrent distribution in two dimensions and the stress field distribution around the crack for antiplane mechanical loading. The analogy is used to show that the supercurrent distribution can be described analytically in terms of a Westergaard function used in elasticity theory. In addition, using a correspondence between the forces acting on a vortex and a crystal dislocation, models for screw dislocation emission from a crack tip are transposed to describe vortex emission from a crack tip. These lead to predictions for the pinning force required to prevent dissipation by vortex emission from the crack tip, as well as for the size of a vortex zone ahead of the crack for different values of the ratio of the applied current to the pinning force.

The formation of TaC and Ta2C by combustion synthesis from their elemental constituents has been studied by time-resolved x-ray diffraction (TRXRD) using synchrotron radiation. The reactions have been followed with a time resolution down to 50 ms. Since the adiabatic temperatures for both reactions are well below any liquidus temperature in the Ta—C phase diagram, no melting occurs and these combustion reactions occur purely in the solid state. The phase transformations associated with these reactions are followed by monitoring the disappearance of reactant and appearance of product powder diffraction peaks in real time as the reaction front propagates through the combusting specimen. In the synthesis of TaC, the results show the formation of the subcarbide (Ta2C phase as an intermediate. In the synthesis of Ta2C, the reaction proceeds directly to the product with no discernible intermediate Ta–C phase within a 50 ms time frame. The chemical dynamics associated with the combustion synthesis of TaC may be described by an initial phase transformation to hexagonal Ta2C arising from carbon diffusion into the Ta metal lattice. As more carbon is available this intermediate subcarbide phase, which has one-half of its octahedral interstices occupied by the carbon, further transforms to the cubic TaC final product, in which all octahedral sites are now occupied. The time-resolved data indicate that the rate of formation of Ta2C is a factor of two faster than that of TaC.

A new method of measuring the mechanical strength of thin films is described. We prepare miniature arrays of four tensile specimens, each 0.25 mm wide, 1 mm long, and 2.2 μm thick, using deposition, patterning, and etching processes common to the semiconductor industry. Each array of four specimens is carried on and protected by a rectangular silicon frame. Thirty-six such specimens are produced on a single wafer. After a specimen frame is mounted, its vertical sides are severed without damaging the specimens. The load is applied by micrometers through a special tension spring. Tensile properties of a 2.2 μm thick Ti–Al–Ti film were determined.

Hot hardness has been measured in seven isostructural Be12X compounds: Be12Cr, Be12Mn, Be12V, Be12Mo, Be12Ti, Be12Ta, and Be12Nb. All vacuum-hot-pressed (VHP) materials exhibited similar hardness levels (800 to 1000 kg/mm2) at low temperatures (<600 °C), but sharply diverged at higher temperatures. Most compounds showed a sharp decrease in hardness above about one-half their melting temperatures except for Be12Nb and Be12Ti which maintained strength until higher temperatures. Ductile-brittle transition temperatures (DBTT's) of 600, 625, 690, 700, 700, and 850 °C were determined for Be12Cr, Be12Mn, Be12V, Be12Mo, Be12Ti, and Be12Nb, respectively. Hot-isostatically-pressed (HIP) and VHP Be12Nb heats both showed comparable behavior, indicating that the temperature required for macroscopic plasticity is not dependent on processing conditions. Differences in slip characteristics were observed between beryllides with similar melting temperatures, but differing DBTT's. Dislocations were activated on multiple slip systems in Bei2V during compressive deformation at 800 °C. Similar behavior was not observed in Be12Nb until test temperatures above 1000 °C. It is proposed that dislocation mobility may be related to the stability between Be12X and Be17X2 phases. Larger refractory metal atoms such as Nb may form faulted layers related to Be17X2 structures and thereby impede deformation at intermediate temperatures. Smaller atoms such as Cr, Mn, V, and Mo do not form a stable Be17X2 phase and thereby allow enhanced dislocation mobility at these temperatures.

The longitudinal ultrasonic velocities of four commercial aluminum alloys and Al(1.8 wt.% Si) were measured between room temperature and the solidus temperatures. In all of the samples, the velocity deviated significantly from a linear temperature dependence at the highest temperatures. In commercially pure (1100) aluminum, this effect is found to be consistent with reported low-frequency damping and elastic modulus changes that are associated with dislocations or grain boundaries. In the four heat-treatable alloys studied, an additional contribution to the nonlinear temperature dependence arises from the dissolution of precipitates at elevated temperatures. Irreversible velocity changes occur during the first heating, as a result of the recovery from work-hardening and heat treatments which were performed during the production of the material. Small hysteretic changes above ∼ 250 °C are correlated with the precipitation and dissolution of alloying elements. The activation energy for the hysteretic changes in Al(1.8% Si) is found to be 0.82 eV, which is consistent with precipitation limited by silicon diffusion along grain boundaries.

Epitaxial body-centered cubic Mo and Cr films have been grown on the (111) surface of α–Fe films on Si(111) at 300 and 575 K by electron beam evaporation in ultrahigh vacuum. X-ray diffraction and transmission electron microscopy show that the Mo films are oriented with the (111) plane parallel to the α-Fe(111) plane and with the Mo[1$\overline 1$0] direction parallel to the Fe[1$\overline 1$0] direction in the plane of the substrate. The same orientation relationship holds for the Cr films epitaxially grown on α-Fe(111) surfaces. Epitaxial Fe(111)/Mo(111)/Fe(111) and Fe(111)/Cr(111)/Fe(111) films have also been grown on Si(111). This work provides new examples of low temperature epitaxy which can occur at a substrate temperature as low as 0.1 times the melting temperature of the deposited materials.

Strained multilayers composed of two misfitting layers and a third, thin interlayer are considered. With appropriate intermediate lattice parameters for the interlayer, the latter is shown to stabilize the structure with respect to misfit dislocation formation. Cases of misfit corresponding both to balanced biaxial stress and to pure shear stress in the interface are treated.

The structural and electronic properties of fluorine- and bromine-intercalated graphite fibers and HOPG are summarized. In contrast to the bromine intercalate, which is purely ionic for any experimentally attainable intercalate concentration, fluorine has a dual ionic and covalent behavior in graphite. Furthermore, whereas bromine-intercalated graphite is ordered, fluorine-intercalated graphite is disordered. The stiff graphene planes are buckled and islands of various fluorine concentrations are formed. A thermodynamic model is proposed that accounts for the differences between fluorine- and bromine-intercalated graphite materials. The model describes the competition between ionically bonded and covalently bonded intercalate phases of fluorine in graphite. Covalent bonding is more favorable energetically, but an important nucleation barrier exists due to strain and to the destruction of the conjugation of the double bonds.

Stages 4–6 FeCl3–graphite intercalation compounds (GIC's) have been prepared by an ordinary two-bulb method, and the bi-intercalation processes of H2SO4 into the GIC's have been studied by x-ray diffraction. Since stages 4–6 FeCl3–GIC's have more than three vacant interlayer spaces in the c-axis repeat distance, the bi-intercalation of H2SO4 into the GIC's takes place stepwise. Consequently, various FeCl3–H2SO4–graphite bi-intercalation compounds (GBC's), from the GBC's with one H2SO4 layer to the GBC's saturated with H2SO4, are obtained in the bi-intercalation processes. Their compositions are described as C6.0nFeCl3 · c(6.0/6.5)H2SO4 from the calculation of structure factor for x-ray diffraction, where n is the stage number of the starting FeCl3-GIC's, and c is the number of H2SO4 layers. Stacking sequences of all the FeCl3–H2SO4–GBC's are also determined.

In the framework of a previously developed kinetic model, a discriminating criterion is established to distinguish between classical and nonclassical nucleation of diamond at solid surfaces. The two-step model gives the non-steady-state nucleation density function in terms of the rate constants for active site → germ, germ → active site, and germ → nucleus kinetic steps. The criterion states that α/β > 6 is a necessary condition for classical nucleation at surfaces to occur, α and β being functions of the rate constants which can be obtained by appropriate analysis of the experimental data. This criterion is applied to recent results on diamond nucleation at silicon surfaces and indicates nonclassical results The expression of the nonequilibrium Zeldovich factor, Z, is also found in the form Z = [1 + K/nd]−1, K and nd being the rate constants for the germ → nucleus and germ → active site steps, respectively. An estimation of the rate constants is reported and the corresponding Zeldovich factor is evaluated to be 0.6 for nucleation at both Si(100) and Si(111) substrates.

The kinetics of MoSi2 pest, caused by oxidation in air, has been studied. Experimental results indicated that pest disintegration occurred at temperatures between 375 and 500 °C. The volumes of test samples increased with oxidation duration. Analysis of change in sample volume versus oxidation duration revealed that the pest disintegration consisted of two stages, namely nucleation (or incubation) and growth. The onset of the growth stage depended on the test temperature. More importantly, changes in sample volume were found to obey a linear relationship with time during the growth stage. Equations were formulated to demonstrate that the growth kinetics of pest disintegration was proportional to the rates of change in sample volume. The rates of volume change during MoSi2 pest were calculated to be 4.9 × 10−6, 2.8 × 10−5, 3.7 × 10−5, and 5.4 × 10−5 cm3/s at 375, 400, 425, and 450 °C, respectively; the growth kinetics increased with oxidation temperature. The activation energy for the growth stage of pest disintegration was determined to be 27.6 kcal/mole, which agrees well with the activation energy for the low-temperature oxidation of MoSi2.

Silicon is an attractive material for the construction of read/write head sliders in magnetic recording applications from the viewpoints of ease of miniaturization and low fabrication cost. In the present investigation we have studied the friction and wear behavior of single-crystal, polycrystalline, ion-implanted, thermally oxidized (wet and dry), and plasma-enhanced chemical vapor deposition (PECVD) oxide-coated silicon pins while sliding against lubricated and unlubricated thin-film disks. For comparison, tests have also been conducted with Al2O3–TiC and Mn–Zn ferrite pins which are currently used as slider materials. With single-crystal silicon the rise in the coefficient of friction with sliding cycles is faster compared to Al2O3–TiC and Mn–Zn ferrite pins. In each case, the rise in friction is associated with the burnishing of the disk surface and transfer of amorphous carbon and lubricant (in the case of lubricated disks) from the disk to the pin. Thermally oxidized (under dry oxygen conditions) single-crystal silicon and PECVD oxide-coated single-crystal silicon exhibit excellent tribological characteristics while sliding against lubricated disks, and we believe this is attributable to the chemical passivity of the oxide coating. In dry nitrogen, the coefficient of friction for single-crystal silicon sliding against lubricated disks behaves differently than in air, decreasing from an initial value of 0.2 to less than 0.05 within 5000 cycles of sliding. We believe that silicon/thin-film disk interface friction and wear is governed by the uniformity and tenacity of the amorphous carbon transfer film and oxygen-enhanced fracture of silicon.