The critical current density of melt-textured YBa2Cu3Ox superconductor has been enhanced by mechanical deformation at a high temperature. Hot deformation at 45° to both the slip plane (001) and the slip directions [100]/[010] has resulted in a high density of dislocation loops and stacking faults. The deformed samples are found to exhibit a critical current density (Jc) at Hc-axis as high as that at Ha-b plane at 1.5 T and 77 K. A Jc of 35300 A/cm2 has been achieved at Hc (1.5 T and 77 K) which is twice as high as that observed in undeformed samples. The enhanced Jc in this magnetic field orientation is attributed to pinning by the defects created by mechanical deformation. This pinning mechanism is found to be effective over a wide angle between the magnetic field and the a-b plane and thus results in a marked reduction in the critical current anisotropy.

When polycarbonate is loaded in tension at room temperature to failure, a certain percentage of the chains are believed to undergo cleavage due to the constraints of entanglements. We present direct evidence that accompanying fracture of polycarbonate, CO molecules are released due to bond scissions.

Superconducting Tl2Ba2CaCu2O8 films were prepared by a two-step postdeposition anneal process under identical conditions on a number of single crystal substrates: (100) LaAlO3, (100) NdGaO3, (100) LaGaO3, (100) SrTiO3, (100) MgO, and (0001) Al2O3. The properties of the resulting Tl2Ba2CaCu2O8 films were strongly dependent on the substrate. Films on all substrates were predominantly c-axis oriented. Films prepared on LaAlO3, NdGaO3, and LaGaO3 also exhibited in-plane epitaxy, while films on MgO, Al2O3, and SrTiO3 were not aligned with the substrates. Some a-axis oriented grains of Tl2Ba2CaCu2O8 formed on NdGaO3 and both a-axis oriented grains and cracks were present on LaGaO3. Large amounts of secondary phases, as indicated by additional peaks in the x-ray diffraction scans, were observed for films on Al2O3 and SrTiO3 and smaller amounts on each of the other substrates. Depth profiling by sputtered neutral mass spectroscopy (SNMS) confirmed the presence of strong film-substrate reactions on Al2O3 and SrTiO3, and also indicated the presence of a reaction on NdGaO3. The Tc onset of the films as measured both inductively and by ac magnetic susceptibility varied depending on the substrate. The highest quality films were prepared on LaAlO3. NdGaO3 may also prove to be an acceptable substrate if the nucleation and growth of a-axis oriented Tl2Ba2CaCu2O8 grains can be eliminated. The remaining substrates appear to be less suitable due to severe film-substrate interactions, lack of epitaxial growth, or crystallographic phase changes.

The solidification processes for the compositions Bi2Sr2CaCu2Oy (2212) and Bi2Sr1.75Ca0.25CuOy (2201) were determined as a function of oxygen partial pressure. During solidification in argon, the superconducting phases were generally not observed to form for either composition. In both cases, the solidus is lowered to approximately 750 °C. Solidification of Bi2Sr1.75Ca0.25CuOy in Ar resulted in a divorced eutectic structure of Bi2Sr2−xCaxOy (22x) and Cu2O while solidification of Bi2Sr2CaCu2Oy in Ar resulted in a divorced eutectic structure of Bi2Sr3−xCaxOy (23x) and Cu2O. Solidification of Bi2Sr1.75Ca0.25CuOy in O2 resulted in large grains of 2201 interspersed with small regions containing the eutectic structure of 22x and CuO/Cu2O. Solidification of Bi2Sr2CaCu2Oy in partial pressures of 1%, 20%, and 100% oxygen resulted in multiphase samples consisting of 2212, 2201, some alkaline-earth cuprates, and both divorced eutectic structures found during solidification in Ar. For both compositions, these latter structures can be attributed to oxygen deficiencies present in the melt regardless of the overpressure of oxygen. These eutectic structures are unstable and convert into the superconducting phases during subsequent anneals in oxygen. The formation process of the 2212 phase during solidification from the melt was determined to proceed through an intermediate state involving the 2201 phase.

An experimental study of the etching properties of defects in diamond using propane flame exposure in air is presented. Both natural diamond crystals and polycrystalline diamond films were exposed to a flame for an optimum time of 3–4 s. This process topographically delineates defects in diamond via an accelerated etch rate at defect sites. Using transmission electron microscopy (TEM) to determine the exact nature and density of defects present in the diamond, we have found a direct correlation between topographical delineation observed by scanning electron microscopy (SEM) and the defect structure observed by TEM.

We present computer simulation results for the planar faults involved in core spreading of 〈100〉 and 〈111〉 dislocations. Seven γ surfaces were computed for different crystallographic planes ({110}, {112}, {123}, {210}, {100}, {111}, and {122}). Stable APB's are observed in the {110} and {112} planes, but they are deviated from the exact 1/2a〈111〉 position. No other stable planar fault was observed. The fact that a stable minimum is observed deviated from the 1/2〈111〉 position suggests the possibility of different dissociation reactions for the 〈111〉 screw dislocation in the {110} and {112} planes. The fact that no other stable minima were observed in the γ surfaces indicates that no true core dissociation is expected for the 〈100〉 dislocations. We propose that dislocation core spreading in various planes can be understood in terms of the directions of lowest restoring forces observed for the corresponding γ surfaces.

Tracer diffusion of 85Sr in polycrystalline Bi2Sr2Can-1CunO2n+4 has been investigated for n = 1, 2, and 3 in an oxygen atmosphere between 775 and 850 °C. A radiotracer serial-sectioning technique was used to measure the concentration profiles, which were fit to a solution of the diffusion equation to calculate the diffusivities. The activation energies were 403, 553, and 519 kJ/mole, for n = 1, 2, and 3, respectively. However, the absolute values of D for the various layered superconductors did not differ by more than an order of magnitude over the measured temperature range. The diffusivity of Sr at 800 °C for n = 1 or 2 over an oxygen partial pressure range of 103 to 105 Pa increased as the pressure decreased.

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.

Optical emission spectroscopy of the rf thermal plasma evaporated YBa2Cu3O7−x has been investigated. The deposited films with the nearly stoichiometric composition could be obtained by using Y-rich powder. From the optical emission spectra, O, Y, Y+, Ba, Ba+, Cu, and YO as the emitting species were observed. The excitation temperature was lower for Y+ than for the other dissociated elements. The relative intensity for YO of a suboxide became larger with a lower plasma torch. It is thought that the deposited film that is poor in Y results from YO sticking to the substrate rather than Y or Y+.

Modifications of a recent model by Izumi et al.1 on diffusion controlled growth of YBa2Cu3O7−x (123) superconductors are proposed, taking into account especially the engulfment process of the Y2BaCuO5 (211) particles into the solidifying 123 interface. The proposed modifications are evidenced by experimental results and applied to explain microstructural features of the 123 superconducting material. In particular, the 1:1 correlation between 123 platelet thickness (planar defect spacing) and 211 particle size as described by Jin et al.2 is explained by an observed bridge growth resulting in a zipper-like mechanism. By this mechanism the platelets grow together in an oriented way leading to a quasi single crystalline material.

We present a description of the thermal behavior of cascades in Cu and Ag over a large energy range and irradiation temperatures. For this purpose the binary collision approximation, which gives the profile of the energy deposition, is coupled to a simplified version of the heat equation. In the present calculations, the original liquid drop model [M. Alurralde, A. Caro, and M. Victoria, J. Nucl. Mater. 183, 33 (1991)] has been extended to the case where the lattice is at finite temperatures. The resulting evolution of the liquid cascade is analyzed for PKA energies up to 1 MeV, and the results are compared to experimental observations of mixing rates. We obtain a temperature dependence that adds to the traditional Radiation Enhanced Diffusion, RED, in very good qualitative agreement with experiments on materials showing thermal spikes.

Superconducting Ba0.6K0.4BiO3 thin films with transition temperatures up to 25 K have been successfully grown on SrTiO3 substrates using RF magnetron sputtering and postgrowth oxygen annealing. Systematic variation of the sputtering process parameters showed that optimum films can be grown on substrates heated to 400 °C in a 10 mTorr atmosphere containing 96% Ar and 4% O2 and using a target containing Ba, K, and Bi in ratios of 0.6:1.2:1.4. High transition temperature superconductivity was observed only in highly oriented, crystalline films having the ideal stoichiometry, Ba0.6K0.4BiO3.

Coatings of three different compositions (Al65Cu20Fe15, Al64Cu18Fe8Cr8, and Al67Cu9Fe10.5Cr10.5Si3) were realized by various thermal deposition techniques. They were studied in the as-deposited state and after annealing. In view of potential applications, these quasicrystalline coatings were examined from the point of view of tribology: friction and wear. Some basic components of friction such as roughness, plowing, and adhesion have been studied in scratch testing. The friction resistance of the coating is strongly dependent on its inherent porosity, hardness, and thickness. The damage of the coatings is essentially brittle though some ductile behavior is observed. Static indentation hardness is in the range 500–600 HV0.03 (5–6 GPa), whereas the scratch hardness varies from 1.4 to 2.4 GPa depending on the percentage of porosity. Friction coefficients (measured at constant load of 20 N) were found to be typically 0.07 and 0.20 for diamond (tip radius R = 0.79 mm) and AISI 52100 (radius R = 0.79 mm) indenters, respectively.

Experimental correlations of thermoelectric power (TEP), oxygen deficiency (δ), and c-lattice constant in YBa2Cu3O7−δ (YBCO) c-oriented, polycrystalline, thin-film, high-temperature oxide superconductors are presented. The TEP values in the normal state were observed to be positive for samples with oxygen deficiencies between 0.08 ≤ δ ≤ 1.00 and negative for 0.00 ≤ δ ≤ 0.08. Furthermore, the TEP magnitudes were highly sensitive to the amount of oxygen and were found to increase with increasing oxygen deficiency, ranging from values of −2 μ V/K to more than two orders of magnitude higher. In addition, relatively temperature-independent TEP values were observed for hole-conductive samples with low oxygen deficiencies (δ ≤ 0.30). The lattice constants (c) of the same samples were measured by XRD. These were found to increase with oxygen deficiency and to correlate systematically with the TEP values. We conclude that TEP is a reliable indicator of the oxygen content in YBCO materials.

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.

High Tc materials containing Bi form glasses when quenched from their melts. These materials pass through a number of intermediate phases when furnace heated, causing chemical segregation along the way; extended annealing is then required to achieve a chemically uniform product. Chemical uniformity is preserved from the glass directly to a high Tc phase by placing the glass suddenly into a furnace at a temperature in which the final product is stable. In addition, it was found possible to hot press the glass flakes into a compact at a sufficiently low temperature without chemical segregation so that a sudden heating step will achieve the same result in bulk material.

Superconducting Bi–Sr–Ca–Cu–O thin films were obtained from post-annealing partially crystallized and amorphous films grown on MgO(100) by pulsed laser deposition. The substrate temperature investigated was in the range of 350–750 °C, over a range of pressure 0.1 to 100 mTorr. The as-deposited films were annealed in 7.5 vol.% O2/Ar or in air at 800–865 °C from several minutes to a few hours. Unlike the pure Bi2Sr2CaCu2O8+δ (2212) phase (Tc = 80 K) which is easily formed after a long continuous period of post-annealing at a temperature below 830 °C, the formation of (Bi, Pb)2Sr2Ca2Cu3O10+δ (2223) phase from the as-deposited amorphous films requires repetitive annealing cycles of short duration in air at 850 °C to simultaneously achieve good crystal quality, small surface roughness, and sharp diamagnetic transition (Tc = 110 K). After annealing, the temperature is lowered down to ∼650 °C by quenching in air and then a slow-cooling step is employed. This procedure was found to enhance the volume fraction of the 2223 phase as compared with a direct slow-cooling process. The trade-off between annealing temperature and time was observed to affect the phase formation and the smoothness of the annealed films. To optimize the post-annealing conditions, Rutherford backscattering spectrometry, x-ray diffraction, and scanning electron microscopy were systematically used to examine the composition, structure, and morphology of the films, respectively.

Chemical interaction between ceramic Y2O3 and Y - Ba-Cu-O liquid with composition close to that of the ternary eutectic is discussed. Intense interaction is observed in the range 930–960 °C that results in the formation of Y2BaCuO5 above 940 °C and YBa2Cu3O6+x plus CuO below 940 °C. At the interface with Y2O3 there is an additional portion containing Y2Cu2O5 or YCuO2. This temperature threshold is exactly that of the peritectic reaction Y2BaCuO5 + L(pl) → YBa2Cu3O6+x + CuO which then appears to control this chemical interaction. The microstructure of the transformed area is oriented in a way that may be used for texturing or crystal growing.

We discuss the results obtained for SrTiO3/YBa2Cu3O7 layers deposited on (001) MgO substrates by UV pulsed laser ablation. Different samples were prepared to study both the growth of a thin (55 nm) layer of SrTiO3 on MgO and the successive epitaxy of a 220 nm YBa2Cu3O7 (YBCO) film on the SrTiO3 layer. An x-ray diffraction (XRD) texture analysis is reported for the bilayers together with resistivity versus temperature and critical current density (Jc) measurements of the superconducting films. The results show that YBCO grains grow with c-axis normal to the surface; the main in-plane orientations are [100] MgO // [100] SrTiO3 // [100] YBCO ([010] YBCO). The XRD line broadening analysis suggests that YBCO columnar grains grow along the whole thickness of the film, also evidencing dislocations and/or faulting separated by a mean distance of 80 nm. The values obtained for the critical current of the superconductor demonstrate the effectiveness of the SrTiO3 intermediate layer in improving the structural quality of the YBCO film.

Growth behavior of YBa2Cu3O7-x (YBCO) thin films from metallic Y–Ba–Cu precursors was investigated. The precursors were prepared by coevaporation of the constituent metallic sources under ultra-high vacuum conditions, and they were oxidized in a load lock chamber and a tube furnace. The grain size of YBCO and degree of crystallographic orientation of the films increased with decreasing oxygen partial pressure p(O2) during transformation of the precursor into the crystal close to the thermodynamic stability line of YBa2Cu3O6.0 in a p(O2) – 1/T phase diagram. The growth of YBCO crystal is controlled by the oxygen diffusion along the c-axis direction of the crystal. The diffusion coefficient of oxygen is determined as D = 1.94 × 1010 exp(−433 000/RT) (cm2/s).