A superconductor ceramic oxide with the Y1Ba2Cu3O7−x phase and exhibiting a transition temperature at Tc ≍92K, was irradiated at room temperature with 1 MeV electrons. It was found that the irradiation produces a sharp drop in the Tc value from 92 K down to ∼40K. The irradiated sample suffered a change from metallike character to semiconductorlike behavior at T > Tc. It is also shown that after irradiation the twin boundaries on the material become irregular.

A tomic mixing resulting from heavy-ion bombardment of thin-film Ni/Pd bilayers and thin Pd markers sandwiched between Ni layers has been investigated. Mixing experiments were performed over a temperature range 40–473 K, using 120 keV Ar+ and 145 keV Kr+ ions at a constant dose rate of 5.5 × 1012 ions cm −2s−1 for doses up to 4 × 1016cm−2. The resulting interdiffusion was measured, in situ, using Rutherford backscattering with 2−2.8 MeV 4He+ ions. The results showed that, for both markers and bilayers, the amount of mixing is similar for both configurations and varies linearly with the square root of the ion dose. Comparison of the induced mixing per ion, following irradiation at 40 K, shows that the mixing is dependent on the damage energy FD deposited at the interface region. The mixing is essentially athermal.

X-ray photoelectron spectroscopy, scanning Auger, and optical microscopy studies of polycrystalline superconducting pellets of Y–Ba–Cu–O/Ag are presented. Silver-laced samples have a lower porosity and a drastically reduced hydrocarbon contamination. Results indicate no detectable substitution of A g into the Y–Ba–Cu–O but a collection of metallic silver in voids and possibly along grain boundaries Intergranular silver could mitigate adverse grain boundary effects in polycrystalline Y–Ba–Cu–O.

Two Ni-modified Al3Ti alloys (Al65Ni10Ti25 and Al62Ni8Ti30) were rapidly solidified by melt spinning. The resulting microstructure was studied using light microscopy and analytical electron microscopy. Significant variations in the microstructure and phases were observed between the two ribbons and through the thickness of each ribbon.A single-phase γ-TiAl structure was seen near the wheel side of the Al62Ni8Ti30 ribbon, having microcrystalline grains ∼ 100 nm in diameter. Second-phase particles of Λ-AlNiTi were found in the remaining regions of that ribbon as the structure became columnar due to reduced rates of cooling. The Al65Ni10Ti25 alloy exhibited a primary phase of π-Al6.5 NiTi2.5. A second phase of μ-Al2NiTi formed with morphology and distribution varying through thickness. Microchemistry measurements on the phases indicated substantial deviations (up to 14 at. %) from the stoichiometric compositions. Further, the π, γ, and μ are low-temperature phases that do not form by solidification under equilibrium conditions. The observation of these phases thus suggests significant undercoolings achieved during the melt-spinning processing of the present alloys. Both ribbons are brittle as spun.

Coble creep, which is controlled by mass transport along grain boundaries, has been identified in a powder-metallurgically prepared nickel aluminide with the nominal composition Ni–22.8Al–0.6Hf–0.1B (at. %). Diffusional creep rates ∊ as a function of temperature T, stress σ, and grain size L are well described by ∊ = 33δb Db Ωσ (kTL3), where δb Db = 3 × 10−6 m3 s−1 × exp [– (313 kJ/mol)/(RT) (δb is the diffusional grain boundary width, Db is the grain boundary diffusivity, R is the gas constant, and T is the absolute temperature). The activation energy of 313 kJ/mol is unusually high as compared to that for volume diffusion.

Binary alloys of Re–Ta, Os–Ta, Ir–Ta, Os–W, and Ir–W were vapor deposited. A wide amorphous formation range was found for all systems, except Ir–W. The crystallization temperatures were generally very high—between 800 and 1000 K.

The Vickers hardness number Hv of a typical glassy inorganic polymer, a-Se, is studied as a function of temperature with the heating rate varied as a parameter from 0.032 to 3 °C/min, over two decades. It is shown that Hv(T), as a function of temperature, goes through a sharp drop in the glass transformation region following the similar drop for the shear modulus G(T) reported previously. By defining an empirical glass transition temperature TG at the inflection point of Hv vs T behavior, the heating rate dependence of TG is examined and interpreted via the kinetic structural relaxation model of glass transformation. It is shown that over the temperature range 36–50 °C the rate of structural relaxation processes controlling the mechanical properties obeys an Arrhenius type of temperature dependence with an activation energy ∼2.75 cV/atom. Furthermore, over the temperature range accessed, the structural relaxation rate seems to follow the viscosity-temperature behavior.

Gax In1 − x Pepilayers grown under a range of growth conditions by organometallic vapor phase epitaxy (OMVPE) on GaAs substrates have been studied in the electron microscope. The results show the presence of an ordering of the group III sublattice parallel to some of the {111} planes. Dark-field images directly reveal ordered domains of different orientations that appear not to be perfect, but contain many planar defects parallel to the growth surface.

A sol-gel method of preparing fine-particle superconducting oxide YBa2Cu3O7−x was developed. Single-phase superconducting oxide YBa2Cu3O7−x formed at temperatures as low as 750°. The particle size obtained by this method was found to be ≤0.2μm. Pellets sintered from these sol-gel powders exhibited very sharp resistivity drops at Tc = 90 °C with a Δc of ∼3°K.

A new hexagonal crystal structure modification of the rhombohedral Mu phase with A7B6 stoichiometry was observed in a cast alloy C-276. The hexagonal structure was determined to share the same lattice parameter along the a axis, while the dimension along the c axis was such that chex = 2/3crhomb. The space group of the hexagonal phase is suggested to be P 63/mmc and forms by a four-layer ABAB repeat, where A and B represent Zr4Al3 and MgCu2 structures, respectively. Details of the diffraction analysis are presented in this article.

Incorporation of bis (trifluoroacetylacetonato) copper (II), Cu (TFA)2 into poly (amide acid) prior to imidization produces bi-and trilayered composite films upon curing. Choice of curing atmosphere and concentration of dopant control the formation of a particular layered structure. Dry air and 100% relative humidity are the curing atmospheres used. The trilayered films are typified by a zero-valent copper layer sandwiched between a thin polyimide overlayer and the bulk polyimide. Curing in 100% relative humidity produces the thinnest overlayer. By doubling the dopant concentration used to prepare the trilayered films, bilayered films will result upon curing. In this instance the lack of a polyimide overlayer affords the oxidation of copper at the surface to copper (II) oxide. In each case the formation of the copper layer results from the migration of all Cu (TFA)2 from a depth of approximately 2000 Å to the surface where subsequent reactions take place. Several [Auger electron spectroscopy (AES), x-ray photoelectron spectroscopy (XPS), transmission electron microscopy (TEM)] analytical techniques are used to characterize the physical and chemical nature of the films.

Atomic mixing in Ni/Pd bilayer films due to 120 keV Ar+ irradiation in the thermally assisted regime (523−673 K) has been measured, in situ, using Rutherford backscattering with 2.0 MeV 4He+ ions. The mean diameter of grains in these polycrystallinc films increased from 10 to 60 nm, following Ar+ bombardment at 573 K. Initial mixing was rapid due to grain boundary diffusion and incorporation of the metal solute into the solvent metal matrix by grain growth; this mixing stage was essentially complete within 10 min for annealed films or after an Ar+ dose of 4 × 1015 cm−2 in irradiated films (10 min irradiation). No further measurable mixing occurred in the annealed, unirradiated films. For the irradiated samples the initial rapid mixing (6−35 atoms/ion) was followed by a slower mixing stage of 0.7–1.8 atoms/ion for irradiation doses of up to 2.5 × 1016 Ar+ cm−2. The Ar+ bombardment gave rise to much smaller mixing levels when the Pd films were deposited on large-grain or single-crystal Ni. A diffusion analysis demonstrates that the effective diffusivity, Deff, for ion-irradiation-enhanced mixing in the thermally assisted regime satisfied the relation Dl < Deff < DB, where the ratio of the grain boundary to lattice diffusivity was DB/Dl > 106.

Powdered samples of the high-temperature superconductors A Ba2Cu3O7−δ (A = Gd,Y) were treated with fluorine gas (100 Torr) at room temperature and 400 °C for varying times (12–64 h). Magnetic shielding measurements on fluorinated products showed that the superconducting volume fraction in treated samples was greatly reduced or even completely eradicated. All samples were structurally characterized by x-ray powder diffraction. Two yttrium samples, one fluorinated at 25 °C and one at 400 °, were also examined by neutron powder diffraction. For samples treated at room temperature, no change in the structure or composition of the products was apparent by either technique. However, samples fluorinated at 400 °C are tetragonal, with a = 3.8641 (3), c = 11.704(1) Å, and bulk composition corresponding to the formula YBa2Cu3F3.5O4.5. Nuclear activation analysis, nuclear reaction analysis, and Auger spectroscopy were used to determine fluorine concentration and distribution in the fluorinated materials. For samples treated at room temperature, fluorine was found primarily within approximately 1 μm of the surface of the product particles. No evidence for a fluorinecontaining superconducting phase was found in any sample; fluorine was found to be detrimental to superconductivity in all cases. These results suggest that the 123 oxides are sensitive to surface effects.

Parametric experiments are described that characterize the process of atomic relocation in Ni/SiO2 bilayers induced by Xe irradiation. The parameters varied are the irradiation temperature (− 196 to + 500 °C) and the Xe irradiation dose (0.01−15 × 1015cm−2). Backscattering spectrometry of the irradiated samples after removal of the unreacted Ni film is the main analytical tool. A phenomenological model is given that describes the results quantitatively. It is deduced that secondary recoil implantation followed by subsequent redistribution within the cascade's lifetime produces the dominant transport mechanism responsible for incorporating Ni into the SiO2.

A new type of brittle fracture was discovered in a Cu–Bi alloy bicrystal with a random misorientation interface. Macroscopically, fracture occurred along the interface with a low-energy release rate of order 50 Jm−2. Microscopically, the crack apparently propagated in a zigzag manner such that a cleavagelike fracture was produced, which consists of two sets of smooth {110} facets and one set of {100} facets with serrations corresponding to their intersections with {111} slip planes. Facet sizes are typically of order 1 by 5 μm or smaller. The very smooth facets and low-energy absorption suggest that a decohesion separation process has occurred along {110} planes, and the serrations suggest that substantial dislocation slip accompanied fracture of the {100} facets. The fracture surface morphology may be explained as the result of a similar morphology of Bi-induced microscopic faceting of the bicrystal interface or, instead, may result from fracture propagating in the vicinity of, but not quite along, the interface. Evidence is presented that favors the latter so that this is a rapid, cleavagelike, semiintergranular fracture that has not been observed in fee metals or alloys when an environment effect is not involved. Its faceted features resemble those of transgranular stress corrosion cracks in certain fee metals.

Metallasiloxanes of the type, M (OSiR3)4, which contain zirconium and hafnium can be prepared by the facile silanol-induced cleavage of organometallic compounds. The metallasiloxanes vary from mobile liquids to insoluble nonmelting powders depending upon the constituents bonded to the silicon. The compounds can be fired into inorganic refractory oxides at temperatures varying from 350–600 °C. The resulting materials have the general formula M Si4O10. Electron spectroscopy for chemical analysis (ESCA) data suggest that the M-O–Si linkage remains intact during this process. Thus the M Si4O10 material can be considered a mixed oxide alloy rather than a simple mixture of the oxides M O2 and SiO2.

The adhesion of diamondlike hard carbon films to silicide forming metals was improved by using an interfacial silicon film several atomic layers thick. The use of thicker (> 10nm) silicon layers results in a decrease in the adhesion, probably due to a degradation of the structural integrity by excessive silicide formation.

Superconducting thin films of the Bi–Sr–Ca–Cu–O system (2 and 10 kÅ) have been successfully prepared by multilayer deposition from elemental metal sources and annealed in N2/O2 mixtures. The onset of the superconducting transition is greater than 80 K with zero resistance at 74 K. The films contain primarily a Bi2(SrCaBi)3Cu2O8 + δ phase with a high degrees of (001) preferred orientation.

Measurements are presented of the electrical double layer and van der Waals forces between the (0001) surfaces of two single-crystal sapphire platelets immersed in an aqueous solution of NaCl at pH values from 6.7 to 11. The results fit the standard Deryaguin-Landau-Verwey-Overbeek (DLVO) theory, with a Hamaker constant of 6.7 × 10−20 J. These are the first measurements made using the Israelachvili surface forces apparatus without mica as a substrate material, and they demonstrate the possibility of using this technique to explore the surface chemistry of a wider range of materials.

The kinetics of the oxidation of dense and porous samples of Ba2 YCu3Ox ceramic have been determined by gravimetric analysis at 400–700 °C. At 600 °C and above, the rate decreases as the thickness of the oxidized layer increases. At 500 °C and below, the kinetics show a linear relation that indicates that the oxidized layer does not protect the ceramic. Dilatometric, microscopic, and high-temperature x-ray data suggest that fractures in the oxide layer at the lower temperatures are caused by the large volume decrease that accompanies the change in oxygen stoichiometry.