High-quality bulk REBa2Cu3O7−x (RE = Y,Eu,Gd,Nd,La) was synthesized by a solution method. Stoichiometric amounts of yttrium, barium, and copper acetates were dissolved in glacial acetic acid. The acid was boiled away leaving a glassy acetate precursor. This precursor has shown amorphous scattering in XRD, a phenomenon consistent with atomic level mixing of reactants. The glassy precursor was subsequently heat-treated with a 5 °C/min ramp to 900 °C and a 2 h soak at 900 °C in air. The final product was obtained after heat treatment under oxygen at 550 °C with slow cooling to room temperature. Final products were analyzed by XRD, SEM, and four probe de-resistivity measurements. The mechanism of both precursor and product formation was examined through substitution studies and XRD. It was found that a combination of a rare earth acetate, barium acetate, and acetic acid was necessary for the formation of an amorphous precursor.

We analyze theoretically the effect of microcracks and voids on the apparent elastic constants of polycrystalline YBa2Cu3O7. Using measurements by Holcomb and Mayo, we calculate crack density and crack aspect ratio. We obtain reasonable intrinsic elastic constants. For the bulk modulus, for example, we predict values close to these obtained by neutron-diffraction studies: 123 GPa for a polycrystal and 122 GPa for a monocrystal.

High-quality YBCO thin films have been grown by Inverted Cylindrical Magnetron Sputtering (ICMS) on LaAlO3(100), SrTiO3(100), SrTiO3(110), and MgO(100) substrates. Transition temperatures of c-axis films exceed 90 K, and transition widths are within 1 K. Critical currents range up to 5 × 106 A/cm2 at 77 K. Structural and morphological features analyzed by x-ray diffraction and scanning electron microscopy, respectively, are found to be strongly dependent on film orientation and deposition temperature. In order to understand such dependence, a simple interpretation is proposed in terms of Gibbs energies and growth dynamics of the nucleation process.

Single crystal fibers of A(B11/2B21/2)O3 perovskites type with compositions Sr(Al1/2Ta1/2)O3 (SAT) and Sr(Al1/2Nb1/2)O3 (SAN) were grown successfully for the first time, using a laser-heated pedestal growth (LHPG) technique. Their crystallographic structures were found to be simple cubic perovskite with lattice parameters a = 3.8952 Å (SAT) and a = 3.8995 Å (SAN) that are close lattice matches to the YBCO superconductors. No structural phase transitions or twins have been found, and the average coefficients of the thermal expansion match well with the YBCO superconductor materials. We report that SAT is one of the most promising substrates to date for the epitaxial growth of HTSC thin films suitable for microwave device applications as it has low dielectric constants (K ∼ 11–12, at 100 Hz–10 GHz and 300 K) and low dielectric loss (∼4 × 10−5 at 10 kHz and 80 K), together with lattice parameter matching, thermal expansion matching, and chemical compatibility with the high Tc superconductors (YBCO).

Thin films (4–1000 Å) of Co were deposited onto n-type 6H-SiC(0001) wafers by UHV electron beam evaporation. The chemistry, microstructure, and electrical properties were determined using x-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and I-V and C-V measurements, respectively. The as-deposited contacts exhibited excellent rectifying behavior with low ideality factors and leakage currents of n < 1.06 and 2.0 × 10−8 A/cm2 at −10 V, respectively. During annealing at 1000 °C for 2 min, significant reaction occurred resulting in the formation of CoSi and graphite. These annealed contacts exhibited ohmic-like character, which is believed to be due to defects created in the interface region.

Single couple thermoelectric generators consisting of n-type FeSi2 and p-type higher manganese silicide were developed and characterized. The leg and the bridge materials were prepared by a powder metallurgical method. Using the Peltier effect the transport properties were measured over the whole working temperature range. Electrical contacts suitable for the hot side could be obtained by conventional vacuum soldering and those for the cold side by ultrasonic soldering. The measured efficiency was in excellent agreement with the calculated values derived from the leg and contact properties.

The elastic properties of carbon nitride (CNx) film adhered to a silicon substrate were characterized through impulsive stimulated thermal scattering (ISTS). The lowest-order pseudo-Rayleigh acoustic mode of the film was excited and monitored optically. From the measured acoustic phase velocities, the elastic moduli of the film were determined. The ISTS technique also permits measurements of the CNx thermal diffusivity. The noninvasive optical measurements described can provide a useful guide to refinements in thin film fabrication procedures and for optimization of mechanical and thermal transport properties.

Crystalline MoS2 films were deposited on Si and graphite substrates using MoF6 and H2S as precursors. The crystal orientation and near-interface structure of the MoS2 films were studied using transmission electron microscopy. In general, the preferred orientation of the (002) basal planes of the MoS2 films with respect to the substrate surface changed from parallel to perpendicular with increased deposition temperature from 320 to 430 °C. At 430 °C, the basal planes were primarily oriented perpendicular to the Si substrate, except for the presence of a ∼5 nm interface region in which the basal planes were oriented in the parallel direction. The formation of this transitional region was also observed on the graphite substrate.

The microstructural changes induced by pulsed laser irradiation in the surface layer of AlN and the initial stage of electroless copper deposition in laser processe specimens have been investigated using transmission electron microscopy (TEM). It was found that a dislocation microstructure is generated by laser processing at laser energy densities of 1.5 J/cm2 or higher. A very sharp change in the dislocation microstructure was seen at a depth of 0.2 to 0.3 μm from the free surface. The dislocation Burgers vector is 〈100〉 and the slip plane is {001}, in agreement with previous reports. AlN was melted and resolidified homo-epitactically from the solid substrate forming a mosaic microstructure with very fine cells having a misorientation of up to 15°. Patches of metallic aluminum were found at the surface of all the specimens irradiated at a laser energy density of 1.5 J/cm2 or higher. Very fine particles of AlN, 20 to 50 nm in diameter, were randomly distributed inside the patches. Immersion of these specimens in an electroless copper bath showed that the electroless solution preferentially etched away aluminum at the Al-AlN interface. At the same time copper islands were deposited in cavities left by AlN particles as well as at the interface with the underlying substrate. These regions are the seeds for further electroless deposition. The TEM observations of laser-induced microstructural changes reported in this paper help to unravel further the mechanisms of adhesion enhancement and surface activation by pulsed laser irradiation.

Mullite-based ceramics added with 0–20 vol % stabilized zirconia have been prepared by alumina/zirconia particles coated with an amorphous silica layer. All samples can be densified through the viscous flow of the amorphous silica layer in the typical temperature range of 1100–1310 °C. For the ZrO2-free mullite ceramics, the viscous densification kinetics is inhibited by increasing the content of the alumina inclusion particles and by crystallization of the amorphous silica layer. However, for the zirconia-mullite ceramics, the addition of the zirconia inclusion particles accelerates the viscous densifcation kinetics. Mullitization kinetics is also enhanced by the addition of zirconia. As the sintering temeperature is high, a porous, duplex microstructure is observed in samples with or without zirconia. Zirconia addition enhances the development of this microstructure. As the sintering temperature and/or zirconia content is increased, ZrO2 particles tend to coarsen, resulting in a decreased tetragonal to monoclinic ratio. Fracture toughness KlC increases with the zirconia content. Mullite-20 vol % ZrO2 composite sintered at 1600 °C has a KlC of 3.8 MPa · m1/2.

Powders and thin films of high-yield lanthanum hexaluminate (LaAl11O18) were prepared by a sol-gel route and compared with yields obtained by conventional hot-pressing of oxide powders. X-ray diffraction and transmission electron microscopy (TEM) were used to characterize powders and thin films deposited on TEM grids. While the solid-state kinetics of formation of LaA11O18 are known to be extremely sluggish, the yield of LaAl11O18 formed by the sol-gel route was much higher than that obtained by processing under similar conditions by solid-state reaction of elemental oxides. The development of a very fine grained microstructure at 1200 °C and a coarser, much more mature microstructure at 1450 °C, with strong texturing of the magnetoplumbite phase, was observed by TEM. Isolated grains of LaAlO3 were present in all powders and films. Trace impurities, introduced most likely as impurities in the initial alumina sol, appear to have segregated to both the grain boundaries and to the external surfaces of grains in as-prepared films.

A novel and easy route for preparing submicrometer particles of zinc oxide, involving hydrolysis of zinc salt in a polyol medium, is proposed. Zinc acetate dihydrate and diethyleneglycol appear to be the best candidates for obtaining a high yield of particles with well-defined morphological characteristics. Monodisperse spherical particles in the submicrometer range (0.2−0.4 μm) have been obtained for a salt concentration less than 0.1 mol 1−1. The particle size depends mainly on the heating rate. The particles are microporous (surface area: 80 m2 g−1) and are formed by aggregation of small crystallites (10 nm). Calcination at moderate temperature drastically reduces this porosity without significant interparticle sintering. At higher concentration, no aggregation occurs and tiny single crystallite particles are obtained.

Hollow ceramic microspheres of Al2O3, SiO2, and mullite have been prepared by the combination of an emulsion technique with a water extraction sol-gel method. Concentration of sol, initial droplet size, and water extraction rate of the system are found to be the important process parameters controlling the size and wall thickness of the hollow microspheres, and their influences are shown. A model that correlates the morphology of microspheres to concentration and water extraction rate is proposed and is in good agreement with the experimental observations. The capability and limitation of this process for forming hollow microspheres are demonstrated. It was shown that hollow microspheres with sizes greater than 5 μm could be readily prepared, while a limitation was met for sizes less than 1 μm, in which case solid microspheres were normally formed.

Silicon nitride is a candidate valve material for internal combustion engines. Its low density and attractive mechanical properties relative to conventional metallic alloys portend significant improvements in valve performance. The production of valves involves a significant amount of machining, especially grinding. Grinding of ceramic materials may result in surface and subsurface damage in the form of fracture or residual stresses which may affect impact behavior and, consequently, the behavior of silicon nitride ceramic materials as valves. The effects of residual stresses due to grinding on the impact wear behavior of one silicon nitride composition ground under various conditions have been investigated.

The stress/strain behavior of bulk material is usually investigated in uniaxial tension or compression; however, these methods are not generally available for very small volumes of material. Submicrometer indentation using a spherical indenter has the potential for filling this gap with, possibly, access to hardness and elastic modulus profiles, representative stress/strain curves, and the strain hardening index. The proposed techniques are based on principles well established in hardness testing using spherical indenters, but not previously applied to depth-sensing instruments capable of measurements on a submicrometer scale. These approaches are now adapted to the analysis of data obtained by stepwise indentation with partial unloading, a technique that facilitates separation of the elastic and plastic components of indentation at each step and is able to take account of the usually ignored phenomena of “piling up” and “sinking in”.

The high-temperature deformation behavior of a SiC whisker-reinforced, yttria-stabilized, tetragonal zirconia polycrystalline composite containing 20 vol % SiC whiskers (SiC/Y-TZP) has been investigated. Tensile tests were performed in vacuum at temperatures from 1450 °C to 1650 °C and at strain rates from 10−3 to 10−5 s−1. The material exhibits useful high-temperature engineering properties (e.g., ∼100 MPa and 16% elongation at T = 1550 °C and at a strain rate of ∼10−4 s−1). The stress exponent was determined to be n ≍ 2. Scanning electron microscopy was used to characterize the grain size and morphology of the composites, both before and after deformation. The grain size in the composite was initially fine, but coarsened at the test temperatures; both dynamic and static grain growth were observed. The morphology of ceramic reinforcements appears to affect strongly the plastic deformation properties of Y-TZP. A comparison is made between the properties of monolithic Y-TZP, 20 wt. % Al2O3 particulate-reinforced Y-TZP (Al2O3/Y-TZP), and SiC/Y-TZP composites.

Physical vapor deposited TiN coatings oxidized by solar beam heat treatment in air were examined by microprobe Raman spectroscopy. The Raman spectra of TiN treated at 400 °C indicated incipient oxidation by the presence of anatase TiO2 and additionally showed a broadband feature around the forbidden TiN vibrational mode. Inhomogeneous mixtures of rutile TiO2 and small amounts of anatase polymorph (< 10%) were detected for the treatments at 600 °C only during the initial stage of oxidation. Prolonged treatment at 600 °C resulted in a complete anatase-to-rutile conversion. Rutile was identified as the single product of oxidation of the TiN samples treated at 800 °C. Peak analysis of the rutile spectra revealed no substantial spectral shifts, demonstrating an oxide growth of nearly stoichiometric rutile with an estimated composition in the range of TiO2±0.02. The Raman scattered light intensity could be correlated with the rutile layer thickness.

We used Monte Carlo simulations to study the kinetics and steady states of B2 and B32 ordering in an equiatomic binary bcc alloy having both thermal and ballistic atom movements. Atom movements occurred by a vacancy mechanism, where first-neighbor atoms exchanged sites with the vacancy. In the thermodynamic case, where this jump probability was set by a Boltzmann factor alone, we found the formation of large amounts of transient B2 (B32) during disorder → B32 (B2) order transformations. The transient order developed in distinct regions, but vanished completely when equilibrium was attained. Ballistic jumps were included as random interchanges of the vacancy with one of its neighboring atoms. Even with small fractions of ballistic jumps, there were large changes in the transient states and steady states of order in the alloy. A kinetic explanation is proposed, in which the presence of ballistic jumps contributed a greater amount of internal energy to the B2 phase than to the B32 phase when there was a strong asymmetry in the second-nearest neighbor pair potentials (VAA2 ↗ VBB2). A two-phase coexistence in the steady state was explained by fluctuations in the local density of ballistic jumps.

AJ-Mg alloy (5052) composite reinforced with Si3N4 particulates was investigated by transmission electron microscopy and electron energy loss spectroscopy. Partial melting was observed at matrix/reinforcement interfaces and matrix grain boundaries at a temperature near an optimum superplastic temperature. Segregation of solute elements (Mg and Si) was observed at the interfaces and grain boundaries. Both partial melting and solute segregation were found to depend on grain boundaries. The obtained results were explained by a decrease of the solidus temperature due to segregation whose extent depends on the type of the grain boundary structure.

The structural transformation of polycrystalline Si induced by high energy ball milling has been studied. The structure and property characteristics of the milled powder have been investigated by x-ray diffraction, scanning electron microscopy, high-resolution electron microscopy, differential scanning calorimetry, Raman scattering, and infrared absorption spectroscopy. Two phase amorphous and nanocrystalline Si has been produced by ball milling of polycrystalline elemental Si. The nanocrystalline components contain some defects such as dislocations, twins, and stacking faults which are typical of defects existing in conventional coarse-grained polycrystalline materials. The volume fraction of amorphous Si is about 15% while the average size of nanocrystalline grains is about 8 nm. Amorphous elemental Si without combined oxygen can be obtained by ball milling. The distribution of amorphous Si and the size of nanocrystalline Si crystallites is not homogeneous in the milled powder. The amorphous Si formed is concentrated near the surface of milled particles while the grain size of nanocrystalline Si ranges from 3 to 20 nm. Structurally, the amorphous silicon component prepared by ball milling is similar to that obtained by ion implantation or chemical vapor deposition. The amorphous Si formed exhibits a crystallization temperature of about 660 °C at a heating rate of 40 K/min and crystallization activation energy of about 268 kJ/mol. Two possible amorphization mechanisms, i.e., pressure-induced amorphization and crystallite-refinement-induced amorphization, are proposed for the amorphization of Si induced by ball milling.