We have performed Rutherford backscattering spectrometry, non-Rutherford proton elastic scattering, and axial ion channeling analysis to determine the composition, the crystallinity, and the epitaxial quality of YBa2Cu3O7 superconducting thin films on (100) SrTiO3 and (100) yttria stabilized zirconia (YSZ) substrates. YBa2Cu3O7 superconducting thin films were fabricated both by high and low temperature laser ablation techniques. The former method requires high temperature annealing in oxygen to recover the superconducting properties, whereas in the latter method as-deposited in situ superconducting thin films are formed at low processing temperatures (500 °C–650 °C). Helium ions in the energy range of 2.0–2.5 MeV were used to determine the relative stoichiometries of the heavier atomic number elements (Y, Ba, Cu) in the film, but are not sensitive enough to determine the relative amount of oxygen in the superconducting phase. The detection sensitivities to oxygen can be greatly enhanced by using the proton elastic scattering [16O(p,p) 16O] reaction, which was found to increase the scattering cross section by a factor of 3 to 5 relative to the Rutherford scattering cross section. The ion-channeling of YBa2Cu3O7 superconducting thin films on (100) SrTiO3 substrates showed excellent minimum channeling yields corresponding to epitaxial growth, but the presence of defects increased the channeling yields for films deposited on (100) YSZ substrates. The ion channeling yields are compared with the microstructure of the films determined by transmission electron microscopy.

We report the results of a systematic examination of the lattice parameters for the YBa2Cu3O7 compound in the 100 K to 110 K temperature range by means of high resolution synchrotron x-ray powder diffraction techniques. The data indicate a linear decrease in the lattice parameters with decreasing temperature over this temperature range. An observed asymmetric broadening of the diffraction peaks is explained by the presence of residual stress in the lattice.

Preliminary results of producing Cu–Y–Ba metallic precursors to high Tc superconductors by high energy ball milling are reported. Mechanical alloying of Cu, Y, and Ba powders (various stoichiometries) produced either amorphous, mixed crystalline/amorphous, or fine grained crystalline powders, as shown by their x-ray spectra. None of the powders exhibited flux exclusion down to a temperature of 1.4 K. The YBa2Cu3 precursor consisted of a mixture of crystalline phases. After being pressed into a pellet and sintered, it was found to be superconducting at liquid nitrogen temperatures.

A process has been developed for the synthesis of YBa2Cu3O7−x superconducting fibers from an organic acid precursor solution. Through rheology measurements on a series of precursor solutions, the molecular structure was determined and subsequently controlled to allow for fiber drawing. For solutions with a viscosity ⋛10 poise, fibers of 1 to 2 m length and 50 ∼ 100 μm diameter can be hand drawn at ≍80 °C. Processing methods were developed to circumvent deformation of the thermoplastic fibers during heating and to minimize BaCO3 formation during decomposition. Fibers sintered at 850 °C for 1 h in 10−2 atm O2, followed by annealing at 500 °C for 4 h in O2, were fully dense, consisted of submicron grains, and were superconducting.

Flux trapping in the 9.3 GHz modulated microwave absorption spectra observed near 4 K from ceramic and powdered ceramic specimens of two separately prepared YBa2Cu3O7-δ samples has been used to separate the intergranular and intragranular contributions to the spectra. In the denser, glassy sample, a broad absorption with a peak near 400 Oe for forward sweeps was observed with appreciable intensity after the maximum flux was trapped. This spectrum is attributed to intergranular junctions, since its relative intensity was reduced on powdering and suspending in wax. In the less dense, more uniform sample, the latter spectrum was appreciably weaker in both ceramic and powder. Both types of junction appear to contribute to the narrow low-field absorption which was observed after zero field cooling in all the samples.

The microstructural development and grain growth of YBa2Cu3O7−y ceramics at 925, 950, and 975 °C were studied. Densification occurred quite rapidly at temperatures below 925 °C. The grain growth of YBa2Cu3O7−y followed a D5 − D50 = Kt relation when sintered at 925 and 950 °C. At 975 °C, the kinetics changed to cubic (D3) behavior, which can be attributed to the formation of a liquid phase at grain boundaries. A trend of decreasing Jc with increasing sintering temperature was observed. Other properties including Tc and the width of the transition were virtually unaffected by the change in microstructure. Without prolonged annealing, a relatively homogeneous oxygen stoichiometry of 6.8 was obtained for fairly dense samples (>93% of theoretical). These results suggest that the oxygenation rate of YBa2Cu3O7−y was quite rapid between the tetragonal phase and the orthorhombic composition of YBa2Cu3O6.8.

Elastic moduli of both as-hot-pressed and oxygenated YBa2Cu3Ox were measured, under isostatic pressures up to 1 GPa, using a combination of strain gage and ultrasonic techniques. Pressurization of the as-hot-pressed samples caused no significant change in moduli; however, pressurization of the oxygenated sample produced a 5-fold increase in bulk modulus. The results show that the significant decreases in moduli between the as-hot-pressed and the oxygenated state were due to extensive microcracking, of an extremely fine nature, that occurred during the oxygenating sequence.

Laser-heated float zone growth was used to study the directional solidification behavior of Bi–Sr–Ca–Cu–O superconductors. The phases that solidify from the melt, their morphology, and their composition are altered by growth rate. Highly textured microstructures are achieved by directional solidification at all growth rates. The superconducting phase is found always to have the composition Bi2.5Sr2CaCu2.2Oy when grown from boules with composition 2:2:1:2 (BiO1.5:SrO:CaO:CuO). Planar growth fronts of Bi2.5Sr2CaCu2.2Oy are observed when the temperature gradient divided by the growth rate (G/R) is larger than 3 ⊠ 1011 K-s/m2 in 2.75 atm oxygen. Thus, the 2212 compound was observed to solidify directly from the melt at the slowest growth rates used in this study. Measurement of the steady-state liquid zone composition indicates that it becomes bismuth-rich as the growth rate decreases. Dendrites of the primary solidification phase, (Sr1−xCax)14Cu24Oy, form in a matrix of Bi2.5Sr2CaCu2.2Oy when G/R is somewhat less than 3 ⊠ 1011 K-s/m2. Observed microstructures are consistent with a peritectic relationship among Bi2.5Sr2CaCu2.2Oy, (Sr1−xCax)14Cu24Oy (x = 0.4), and a liquid rich in bismuth at elevated oxygen pressure. At lower values of G/R, Sr3Ca2Cu5Oy is the primary solidification phase and negligible Bi2.5Sr2CaCu2.2Oy forms in the matrix.

A high Tc superconducting (Bi, Pb)–Sr–Ca–Cu–O filament was prepared using a combined technique of suspension spinning and densification of the pyrolyzed filaments by pressing and sintering. The effects of the Jc of the filament obtained on the spinning and densifying conditions were examined. The Jc was dependent on the composition of the starting powder and the kind of suspension medium. The Jc was strongly affected by the pyrolyzed condition and densification time. The highest Jc value at 77 K, 0 T of 1900 A/cm2 was attained for the filament sintered under the optimum sintering condition. The grains in the filament were oriented with the c axis perpendicular to the filament surface, and the coupling of the grains in the perpendicular to the filament surface was weaker than that for the parallel direction in the filament surface.

A study is made of the effects of annealing both La2−xSrxCuO4 (for x = 0, 0.1, and 0.15) and YBa2Cu3O7 in wet and dry O2 atmospheres at various temperatures between 200 and 930 °C. In the case of La2−xSrxSrCuO4, substantial degradation of resistive properties occurs during annealing in moist O2, the degradation being highest at 200 °C and decreasing as the treatment temperature increases. Since the Meissner effect remains unaffected, it is concluded that degradation is due to the formation of a hydroxide species at grain boundaries, which decomposes as the anneal temperature is increased to 930 °C. In the case of YBa2Cu3O7, on the other hand, moisture does not produce degradation for anneals at 200 °C and above, but severe degradation of resistive behavior does occur for dry O2 anneals, with a maximum effect at 500 °C. It is found that this effect results from a contaminant gas, possibly CO2, absorbed by the furnace when it is open to air. Again, the degradation is due to formation of a grain-boundary phase which decomposes by annealing at 930 °C.

An experiment was designed to follow the formation of higher member phases from lower member phases in the Tl2Can−1Ba2CunO2n+4 series. Coarse particles of the lower member phase were directly interfaced with various Ca–Cu–O sources and the pressed pellets were heat treated in air in a gold pocket at 850 °C for a period of 2–4 h. The reacted samples were polished and examined by scanning electron microscopy with energy dispersive x-ray spectrometry analysis (EDS). For the 2021 based reaction systems, the results suggest that the 2122 phase can be formed via reactions which involve the decomposition of the 2021 phase, the formation of a complex liquid phase, and finally the reaction between this liquid phase and a Ba/Ca compound. The formation of the 2223 phase from the 2122 phase is likely to follow a similar reaction route. The involvement of a liquid phase in the formation of the higher member phases may lead to a glassy phase, and hence to a barrier to the achievement of a high critical current density.

Scanning and isothermal calorimetry, together with x-ray diffraction and high resolution transmission electron microscopy (TEM), have been used to characterize Al–Mn and Al–Mn–Si films sputtered onto substrates at 60 °C, 45 °C, and −100 °C. In the case of Al0.83Mn0.17, the monotonically decreasing isothermal calorimetric signal, characteristic of a grain growth process, has proved decisive in identifying the as-sputtered “amorphous” state as microquasicrystalline, with an average grain size of ∼ 20 Å, in agreement with an estimate of correlation range from the x-ray pattern. The TEM at 400 keV reveals well-defined atomic or lattice images in annealed films but only barely resolved grains (ordered clusters) in the as-sputtered films. The relation between the metallic glass and the microquasicrystalline state in these alloys is discussed.

The solid solubility of magnesium in titanium under equilibrium conditions is reported to be extremely small. Mechanical alloying of a mixture of titanium and magnesium powders resulted in the formation of nanocrystalline (10–15 nm in size) grains of Ti–Mg solid solution. This solid solution has a metastable fcc structure with a = 0.426 nm and contains about 3 wt.% (6 at.%) magnesium in it. It is suggested that the fcc structure has formed as a result of the heavy mechanical deformation of the hep structure introduced during milling. High temperature annealing of the metastable solid solution led to its decomposition forming the equilibrium phases, viz., elemental titanium and magnesium.

The structure of Ti4Ni4Si7 is studied using powder neutron diffraction and Rietveld analysis. Prccise determination of the crystalline parameters, atomic positions, and temperature factors is achieved. A criterion previously elaborated for the phase TiFeSi2 is used to determine the coordination number. From the arrangement of the atoms in the unit cell and their interbond distances, we find that Si atoms are nearest neighbors to Ti and Ni. An extension of the same criterion shows that Ti–Ni and Ni–Si hybridization is likely to be strong while Ti–Ni hybridization is weak. A comparison with mono- and disilicides is made.

Optical metallography, scanning electron microscopy, electron microprobe analysis, and transmission electron microscopy were used to characterize metallurgical grade silicon, produced in an electric are furnace. Coincidence fraction determinations were assumed to be Σ7 and Σ9 when grain boundaries are underlined by precipitated phases and Σ3 when they are not. The study of intergranular compounds was emphasized; ten compounds were found, the main ones being Si2Ca, Si8Al6Fe4Ca, Si2Al2Ca, Si2FeTi, and Si2.4Fe (α leboitc). The precipitation of these compounds was discussed according to the principal impurity concentrations in silicon. The crystalline structure of Si8Al6Fe4Ca was determined to be triclinic with a = 1.3923 nm, b = 1.3896 nm, c = 1.3900 nm and α = 92.4°, β = 110.3°, γ = 119.9°.

A change in microstructure, including dislocation Burgers vector, length, and behavior, has been observed to occur when the epilayer mismatch is varied in GexSi1−x layers grown on (100) Si. At low mismatches (<1.5%), there is an orthogonal array of very long 60° misfit dislocations. At higher mismatches (>2.3%) there is an orthogonal array of short edge dislocations. At intermediate mismatches (1.5 to 2.3%) there is a mixture of 60° and edge dislocations. The nature of the microstructure has a pronounced effect on the density of threading dislocations in the epilayer, which increase by a factor of ∼60× through a relatively small range of mismatch (1.7 to 2.1%, corresponding to x ranging from 0.4 to 0.5). These morphologies are discussed in the light of recent work on the sources of misfit dislocations. While mechanisms for the introduction and propagation of dislocations at low mismatch have recently been observed and explained, the high misfit case is clearly very different; i.e., surface nucleation seems to be likely in the latter case as opposed to operation of an internal source in the former. A mechanism for edge dislocation formation is proposed.

An analysis of nucleation from solid nuclei in Polix photovoltaic polycrystalline silicon is reported. The bulk texture is studied by neutron diffraction using a transmission method. The crystallographic orientation is determined for three adjacent samples along the growth axis in the lower central part of the ingot. The size and orientation of all crystallites are obtained in the domains showing different morphologies: a nucleation zone with equiaxed crystallites, an upper domain with columnar structure, and an intermediate part where both types of crystallization are present. The crystallites are counted in terms of their volume in the three parts. The mean grain size increases in the columnar domain, but a pronounced elimination of particular crystalline orientations is not observed as the morphology is changed.

The surface morphology of SIMOX wafers implanted at 180 keV with doses of 0.4–2.2 ⊠ 101816O+ cm−2 in a temperature range of 400–700 °C has been investigated using transmission electron microscopy (TEM) replica and cross-sectional TEM (XTEM) techniques. Wafer temperature during oxygen implantation strongly affects the morphology. A number of dents are formed on the surface of wafers implanted at temperatures higher than 510 °C with a dose of 1.8 ⊠ 1018 cm−2. Increasing the wafer temperature causes the dents to grow. The dents disappear by a high-temperature anneal of 1260 °C after the implantation. It is found that oxygen implantation through a 50-nm-thick screen oxide film prevents dent formation. A model explaining the dent formation and dent growth is also proposed.

The reduction of propagation losses in ZnO thin film waveguides for integrated optics after CO2 laser treatment is studied. RHEED patterns show that the measured decrease of optical losses is accompanied by an increase of ordering after the laser treatment. The reordering depends on the initial film state and the laser irradiation conditions.

The ferroelectric to paraelectric phase transition in lithium niobate is examined. The present study focuses on the microscopic mechanism for this phase transition. Literature reports that give insight into this mechanism are reviewed. Two alternate mechanisms for this second order transition have been discussed previously. The phase transition has been proposed to occur by either (a) cooperative displacement of Li ions or (b) statistical disordering of Li between two octahedral sites in the structure. The present study develops a general Landau expression for the second order phase transition. The spontaneous polarization of the lattice is used as an indicator of the extent of transformation. Then both displacement and disordering models are explored. These are compared with the observed spontaneous polarization data. It is concluded that the spontaneous polarization data are indicative of a Li disordering model, rather than a Li displacement model.