Via in situ electrical property measurements (conductivity, Seebeck coefficient) over the temperature range 500–800 °C and oxygen partial pressure range 10−4-1 atm, the equilibrium transport properties and stability range of YBa2Cu4O8 were determined. YBa2Cu4O8 behaves like the intrinsically mixed-valent compound, magnetite (Fe3O4), with small variations in electrical properties with changes in oxygen partial pressure. The decomposition boundary to YBa2Cu3O6+y (or YBa2Cu3.5O7.5±z) and CuO occurs at log(po2, atm) = −1.24 × 104/T(K) + 11.01(773 ⋚ T(K) ⋚ 1073).

An alternative synthetic approach was attempted for the fabrication of the Bi–Ca–Sr–Cu oxide superconductor. In this approach a mixed Sr–Ca–Cu oxide powder was first formed, and the resulting powder was subsequently reacted with Bi2O3. With this reaction scheme, problems associated with the low reactivity of CuO and SrCO3 can be partially removed by converting the mixed oxide/carbonate precursors to the reactive Sr–Ca–Cu compound. An enhanced rate of formation of the high-Tc (110 K) phase was observed in the two-step reaction, and this was explained in terms of the low activation free energy path for the formation of the high-Tc phase, which increased the decomposition rate of the remnant CuO. Under the condition of rapid heating, the formation of the high-Tc phase in the one-step reaction was expedited by the Cu-rich liquid phase. However, the liquid phase caused the formation of an insulating layer between the superconducting grains in spite of its catalytic activity in the high-Tc phase formation.

Nearly single phase sintered samples of the lead-doped high-Tc oxide superconductor of nominal composition Bi1.6Pb0.4Ca2Sr2Cu3Ox have been prepared using a precursor matrix reaction method. The experimental results indicate that in samples annealed under optimum conditions (200 h at 855 °C) the volume fraction of impurity phases is only about 3%. If the optimum annealing time is exceeded, the high-Tc phase begins to decompose into the low-Tc phase and nonsuperconducting phases. It is found that the precursor reaction matrix method minimizes loss of lead during processing.

Thin films of Y1Ba2Cu3O7−x have been prepared on MgO, SrTiO3/Al2O3, and Al2O3 substrates by rf magnetron sputtering. A buffer layer of SrTiO3 was deposited on Al2O3 by flash evaporation. The as-deposited films on MgO and SrTiO

Magnetic shields for SQUID applications were successfully fabricated using high Tc superconducting Bi–Sr–Ca–Cu–O (BSCCO). In order to produce shields with adequate superconducting properties and close dimensional control, it was necessary to develop several new processing techniques. Shields were produced by casting liquid BSCCO into molds, heat treating, and machining. A series of BSCCO alloys with different compositions were cast from the molten state into metal molds and subsequently heat treated to render the castings superconducting. The heat-treating cycles were studied with the aid of thermogravimetric analysis (TGA), differential thermal analysis (DTA), and dilatometer measurements. The phases and microstructures after various heat-treating cycles were monitored by x-ray diffraction (XRD), optical microscopy, and scanning electron microscopy (SEM). Superconducting properties were measured after various stages of heat treatment and machining. Prototype magnetic shields were machined from bulk castings and found to perform successfully. The most significant factor in shield quality was the nominal composition of the shield, which was shown by transmission electron microscopy (TEM) to affect the grain boundary chemistry.

A 1/1-type approximant to the AlCuCr icosahedral phase and approximants to a decagonal phase have been found in an as-cast Al65Cu20Cr15 ingot. Selected area electron diffraction indicates that the 1/1-type approximant consists of Mackay icosahedra arranged on a bcc lattice, similar to the α-AlMnSi cubic phase. Ordering of the glue atoms produces a base-centered orthorhombic superstructure, making the overall structure monoclinic P2/m, with lattice parameters a = 12.6 Å, c = 17.92 Å, and α = 90°.

Superconducting Tl–Ca–Ba–Cu–oxide films have been prepared on yttria stabilized zirconia substrates via the reaction of Tl2O vapor with precursor Ca–Ba–Cu–oxide films prepared by the spray pyrolysis of a solution of the metal nitrates. The vapor reaction process, evaluated in both air and oxygen ambients, was carried out in a two-zone reactor which permitted the independent control of the temperatures of the sample and of a boat containing thallium oxide. Sample temperatures of 865–905 °C and boat temperatures of 775–870 °C were investigated. X-ray diffraction analysis of the best samples, which were prepared in an oxygen ambient at sample temperatures of 895–900 °C and boat temperatures of 805–810 °C, revealed the presence of a highly oriented Tl2Ca2Ba2Cu3O10+y phase with a trace of the Tl2CaBa2Cu2O8+y phase. FWHM's of ∼2°θ were obtained in x-ray rocking curve analyses of the oriented 2223 phase. Tc (0) values of 95–105 K were measured for the better samples, and a zero field critical current density of 28 800 amps/cm2 was measured at 77 K for the best sample. SEM micrographs taken of the highest Jc samples reveal a highly textured structure consisting of platelike crystals.

Eshelby's equivalent inclusion method is applied to the case of a single, inhomogeneous, ellipsoidal precipitate in an infinite matrix to study the morphological changes of the gamma-prime precipitates in nickel-base superalloys due to the influence of lattice constant misfit, elastic inhomogeneity and anisotropy, applied stress, and interfacial energy. The energy-minimizing inclusion shapes depend very sensitively on the degree of elastic inhomogeneity, on the sense and magnitude of the applied stress, and on the sense of the lattice constant misfit. The interfacial energy contribution can dominate that of elastic strain energy for small precipitate sizes, elastically compliant systems, nearly homogeneous alloys, and/or nearly isotropic materials. Calculations are carried out for two well-characterized nickel-base alloys: a Ni–13.5Al alloy (positive misfit, elastically hard inclusions) studied by Miyazaki et al. and CMSX-3 (negative misfit, elastically soft inclusions) studied by Pollock. The Eshelby energy calculations correctly predict the precipitate morphologies observed by Miyazaki et al. and by Pollock.

Two types of platinum group metal particles were found in borosilicate nuclear waste glasses: needle-shaped RuO2 particles and spherical PdRhxTey alloys. They form a dense sediment of high electrical conductivity and relatively high viscosity at the bottom of the ceramic melting furnace. The sludge shows a non-Newtonian flow behavior. The viscosity and conductivity of the sludge depend not only on the platinum group metal content but also on the texture and morphology of the RuO2 particles. RuO2 forms long, needle-shaped crystals which are caused by alkalimolybdate salt melts that formed in the calcine layer. The salt melts oxidize the Ru present as small RuO2 particles after calcination to higher oxidation states. Ruthenium (VI) compounds are formed, presumably, which are not stable with respect to RuO2 under the melting conditions. RuO2 precipitates and crystallizes into long, needle-like particles.

Superconducting Y1Ba2Cu3O7−δ films were prepared on the MgO (100) and SrTiO3 (100) single crystals using metal organic chemical vapor deposition (MOCVD) of β-diketone metal chelates of Y(thd)3, Ba(th)2, and Cu(thd)2. The evaporation kinetics of Y(thd)3, Ba(thd)2, and Cu(thd)2 and the ratios of deposited to evaporated mole percents of Y, Ba, and Cu cations were studied. The microstructure of Y1Ba2Cu3O7−δ films deposited using MOCVD was observed using scanning electron microscopy and transmission electron microscopy to investigate surface morphology change with the film composition and transformation twin structures. The experimental results showed that the volatility of Ba(thd)2 did not perceptively increase with decreasing evaporation pressure from 10 Torr to 5 Torr, but that of Y(thd)3 or Cu(thd)2 increased with the pressure decrease. The ratio of deposited to evaporated mole percents of Ba cation was smaller than those of Y and Cu cations. Therefore, Ba must be evaporated more than the stoichiometric amount for Y1Ba2Cu3O7−δ in order to obtain single phase Y1Ba2Cu3O7−δ films. The surface morphology of the Y1Ba2Cu3O7−δ films showed perculiar changes with slight composition changes. The transition onset and zero resistance temperatures of typical stoichiometric film deposited on MgO were 93 K and 91 K, respectively. The Y1Ba2Cu3O7−δ films had about 50 nm grain size, and most grains consisted of transformation twins. The critical current density of a film deposited on SrTiO3 was 105 A/cm2 at 77 K and zero magnetic field.

Fission fragment damage was introduced into aligned sintered samples of various superconductors containing small additions of UO2 by irradiation with thermal neutrons. Samples of aligned, sintered YBa2Cu3Ox, powdered Bi2Sr2Ca1Cu2Oy, powdered Bi1.7Pb0.3Sr2Ca2Cu3Oz, and epitaxial films of YBa2Cu3Ox on (100)SrTiO3 were used. Magnetic hysteresis, with the critical state model, was used to evaluate changes in the intragranular critical current. In the case of the Bi1.7Pb0.3Sr2Ca2Cu3Oz powders an increase in intragranular Jc at 0.8 T of greater than 70 times was produced by the radiation. The epitaxial film showed no change in Jc on irradiation. This behavior upon irradiation is attributed to the pinning caused by damage produced by the fission products of uranium.

Bi2.1Sr1.8Cu2O8 fibers having excellent superconducting properties can be grown by a laser-heated float zone process. In order to maintain stable growth conditions and thereby obtain fibers free of diameter fluctuations and voids, dense ceramic starting material containing only the 2212 phase is required. In this study various processing parameters, including calcining and sintering temperatures and times, grain size of the powders used, and pressing pressures were optimized to yield dense, chemically homogeneous starting material. It was found that under most conditions there was no increase in the density on sintering. Retrograde densification was the usual situation except at higher pressures and was found to depend on pressing pressure, calcination history, and sintering temperature. Cold-pressing at higher pressures (100000 psi) yielded denser but chemically inhomogeneous material. Ceramic samples sintered for long times (>48 h) yielded source rods that produced instabilities during fiber growth, presumably due to preferential loss of mass during sintering.

Submicron YBa2Cu3O7−δ particles have been produced in an aerosol flame reactor by a spray pyrolysis method in which an aerosol composed of an aqueous solution of Y, Ba, and Cu nitrate salts was introduced into a flame. It was observed that the configuration of the flame is particularly important for the successful application of the method. A premixed flame gave particles with an x-ray diffraction pattern resembling the XRD spectra of materials exposed to high concentrations of water vapor. An over-ventilated diffusion flame configuration produced the desired result: submicron unagglomerated, solid crystalline particles with Tc = 92 K.

Fine powders of intermetallic NiAl and Ni3Al were synthesized through organometallic precursors, which were coprecipitated from aqueous solutions of NiCl2 and AlCl3 by the addition of ammonium benzoate and hydradinium monochloride as precipitants. Ni3Al and NiAl were synthesized by a two-step heat treatment of the precursors. The initial step was the thermal decomposition of organic groups to form homogeneous mixtures of Ni3C, amorphous Al2O3, and free C below 1000 °C. The other step was the reaction above 1300 °C to form the intermetallics. Single phase powders of NiAl and Ni3Al with the particle size less than 3 μm were obtained above 1300 and 1400 °C, respectively.

The mechanical properties of single-quasicrystals of decagonal AlCoCuSi have been studied for the first time by applying the Vickers indentation method. The hardness has been determined as H ≃ 9.6 MPa. Estimates for the modulus of elasticity and the fracture toughness are given. The quasicrystals are highly strained internally. Scratching experiments show slight anisotropies in the abrasive friction coefficient. The dominant abrasive mechanism is microplowing.

Evidence of directional structural disordering prior to complete amorphization of Cu4Ti3 during 2 MeV electron irradiation is presented. It is shown that the observed disordering is intrinsic to the irradiated material and is incommensurate with the structure of the crystalline compound. The results point to the presence of significant anisotropy in the response of the material to irradiation. A model based on local rotation of clusters of atoms within a partially chemically-disordered matrix is developed. These results are discussed in relation to recent proposed mechanisms of amorphization based on volume expansion. The questions raised by this work indicate a need for detailed studies of the atomic level structural evolution of a material during solid state amorphization.

Determination of the boundary fractal dimension of planar sections through particles produced by fracturing a series of brittle intermetallic V3Au materials with increasing oxygen content provides a single parameter that describes the surface roughness. This is observed to correlate with the measured fracture toughness, K1c, as determined with an indentation cracking test. The correlation agrees quantitatively with results obtained on several brittle ceramics by other workers.

Superconducting Bi1.84Pb0.34Sr2.03Ca1.9Cu3.06Oy thick films were prepared on MgO substrates by screen printing with the powder consisting almost entirely of the 110 K phase. The thick film sandwiched between the two MgO substrates was then hot-pressed in air under various conditions. The thickness of the film was 20–40 μm. The degree of grain orientation was quantitatively evaluated through the image analysis on the SEM micrographs for the chemically etched cross sections of the samples. The degree of grain orientation and the critical current density (Jc) increased with increasing hot-pressing temperature. When hot-pressed at 855 °C under a constant pressure of 500 kg/cm2 for 270 min, the Jc had a maximum value of 9500 A/cm2 (77 K, 0 Oe), and the critical temperature was 110 K. When the hot-pressing pressure was higher than 200 kg/cm2, the degree of grain orientation was almost independent of hot-pressing pressure. Nevertheless, the Jc increased with increasing hot-pressing pressure. The relationship between the magnetic field dependence of Jc and hot-pressing conditions was examined.

Superconducting films in the Bi–Sr–Ca–Cu–O systems were made using metal alkoxides. To prepare a dip-coating solution using a mixed alkoxide solution, insoluble Cu and Bi alkoxides were dissolved by modification with 2-dimethylaminoethanol and formation of a double alkoxide, respectively. Formation of the double alkoxides of Bi with Ca or Sr was confirmed using FT-IR and 1H-NMR. Bi–Sr–Ca–Cu–O films on yttria-stabilized ZrO2 and single crystal MgO(100) substrates were made using this solution. The films were closely oriented along the c-axis perpendicular to the substrate. The film on MgO(100) fired at 850 °C for 48 h showed two resistance drops around 115 and 85 K, corresponding to the high-Tc and low-Tc phases, respectively, and zero resistance at 72 K.

The energies and configurations of interstitials and vacancies in the ordered compounds CuTi and CuTi2 were determined using atomistic simulation with realistic embedded-atom potentials. The formation energy of an antisite pair was found to be 0.385 and 0.460 eV in CuTi and CuTi2, respectively. In both compounds, the creation of a vacancy by the removal of either a Cu or Ti atom resulted in a vacant Cu site, with an adjacent antisite defect in the case of the Ti vacancy. The vacant Cu site in CuTi was found to be very mobile within two adjacent (001) Cu planes, with a migration energy of 0.19 eV, giving rise to two-dimensional migration. The vacancy migration energy across (001) Ti planes, however, was 1.32 eV, which could be lowered to 0.75 or 0.60 eV if one or two Cu antisite defects were initially present in these planes. In CuTi2, the vacancy migration energy of 0.92 eV along the (001) Cu plane was significantly higher than in CuTi. The effective vacancy formation energies were calculated to be 1.09 eV and 0.90 eV in CuTi and CuTi2, respectively. Interstitials created by inserting either a Cu or Ti atom had complicated configurations in which a Cu 〈111〉 split interstitial was surrounded by two or three Ti antisite defects. The interstitial formation energy was estimated to be 1.7 eV in CuTi and 1.9 eV in CuTi2.