A method for the complete removal of twins from single crystals of superconducting YBa2Cu3O7−x is described. The process depends on ferroelastic behavior found to exist in the phase, and should be generally applicable to the layered perovskite-type phases containing accommodation twins resulting from a tetragonal-to-orthorhombic transformation on cooling. The twin-free, superconducting single crystals will enable investigation of a–b anisotropy of properties as well as crystal structure determination without complication by the presence of microtwins.

We present the results of an electron microscopy study of Pb-substitution in bulk Bi–Sr–Ca–Cu–O superconductors. We observe grains with c-axis lattice parameters of 30.8 Å (2212 phase), 36.7 Å (2223 phase), and 43.2 Å (2234 phase) containing no intergrowth defects. The existence of two separate incommensurate superstructures, Q1 and Q2, which were previously observed in Pb-doped ceramics and single crystals, has been confirmed in this study. It is found that superlattice reflections from the Q2,-modulated structure in the 2223 phase are much weaker than those from the Q2-modulation, whereas the diffraction intensities of the Q1- and Q2-modulations in the 2212 phase are similar. We also show that the periodicity along the b-axis of the Q2-modulation increases with increasing Pb-substitution, contrary to the implications of a previously suggested structural model.

In the processing of the high temperature superconductors RE1Ba2Cu3O7−x a knowledge of the liquidus temperatures is required in order to avoid liquid formation during the initial reactions of the starting materials. We have investigated the invariant points on the liquidus surface of the RE–Ba–Cu–O systems for RE = Y, Er, Gd, and Nd in oxygen, air, and argon, While the temperatures of the low melting reactions are almost independent of the rare earth species, they are heavily dependent on oxygen partial pressure. In addition, the peritectic decomposition temperature of the REBa2Cu3O7 phase was found to be a function of rare earth with a significantly higher value for the Nd compound than for the other rare earths.

Copper/nickel multilayered thin-films prepared by electrodeposition have been examined in cross section by electron energy loss spectroscopy and high-resolution transmission electron microscopy. The results of the examinations provide the first direct experimental evidence of the large composition modulation across successive layers in the thin-film structure and the coherent nature of Cu/Ni interfaces.

Gamma-ray-induced surface defects in YBa2Cu3Ox (x ≈ 7) have been investigated by thermally stimulated luminescence (TSL) following storage of the samples in dry (vacuum), oxygen, and 98% relative humidity environments. Irradiation of samples stored in either vacuum or oxygen environments shows that no insulating chemical species are formed on the surface of the superconductor. In contrast, exposure to the humid environment produces various chemical components on the surface, and, consequently, enhances the TSL yield. Comparison of the YBa2Cu3Ox, TSL glow curve and emission spectra with those of BaCO3 suggests that one of the components contributing to the purported YBa2Cu3Ox luminescence is BaCO3. Evidence for formation of other chemical species and the suitability of the TSL technique for their determination are discussed.

The reaction product from an oxide mixture of 1Pb:2Sr:0.75Y:25Ca:2Cu at 960 °C was nearly single phase. The crystal structure of a single crystal, selected from the reaction product, was determined from three-dimensional x-ray diffraction data. The stoichiometry was found to be Pb0.71Cu0.29Sr2(Y0.73Ca0.27)Cu2O7. The tetragonal lattice constants are a = 3.8207(4) Å, c = 11.826(1) Å, space group P4/mmm, Mr = 655.6, Z = 1, Dx, = 6.31 g cm−3, λ(MoKα) = 0.71069 Å. R = 0.0269 for 179 unique observed reflections. The crystal structure is isomorphous with the 1212 phases. The Pb ion at the origin has an occupancy of 0.705 (8) and a Cu ion is located at 0.221, 0, 0 with an occupancy of 0.295. The oxygen ion in the plane of the Pb ions is disordered over a fourfold site with an occupancy of one. An ordered arrangement of this oxygen ion results in a distorted environment for periodically repeated Pb ions. The Pb–O bond lengths to the two oxygen ions above and below the Pb plane are 1.968(14) Å. The Cu ion, displaced from the origin, can be considered as tetrahedrally coordinated. The four Cu–O bond distances in the CuO2 plane are 1.917(6) Å and the bond length to a fifth oxygen atom is 2.304(14) Å at the apex of the square pyramid. A valence sum calculation for Cu in square coplanar coordination yields a value of 2.01. A similar calculation for Cu in the tetrahedral site yields 1.5. Sr is in a monocapped square antiprism coordination polyhedron. Y and Ca atoms occupy statistically the same site and are in cubic coordination. The structure can be described as consisting of CuO2–(Y, Ca)–CuO2 layers with PbO6 octahedra flanking the layers and Sr in the oxygen interstice. The compound is metallic at room temperature and shows no superconducting transition to 20 K.

Phase formation in the system Bi–Sr–Cu–O has been examined as a function of composition, temperature, ambient atmosphere, cooling history, and annealing time. Ceramic processing and melt crystallization techniques were used. For the ceramic materials (using Bi2O3, SrCO3, and CuO) processed at 700 °C in air the Bi2Sr2CuO6 composition (221) crystallizes to a mixture of CuO, SrCO3, and the rhombohedral Bi2O3 · xSrO solid solution. At 800–830 °C in air for short durations (5 min to 2 h) the reacted products consist principally of the ideal 221 phase with minor amounts of CuO. For longer reaction times (2–400 h) the reacted products consist of the ideal 221-type structure with c = 24.64 Å and a = 3.804 Å, a “collapsed” 221 structure with c = 23.6 Å, and CuO. With increasing reaction time the “collapsed” 221 phase grows gradually at the expense of the ideal 221 phase. The “collapsed” 221 phase is not an oxycarbonate and appears to be a distinct ternary compound near the 221 composition, with a layered structure having a 1 Å smaller stacking repeat. The ideal 221 phase is a solid solution with variable Sr content. With decreasing Sr in the starting mixture [2 to 1.25 atoms per formula unit (afu)] we observe the following: (1) the formation of the “collapsed” 221 structure is inhibited; (2) for the ideal 221 phase the c-cell dimension decreases significantly (0.2 Å) and the a-cell dimension increases slightly (0.02 Å); (3) the low temperature resistivity behavior changes from superconducting with Tc onset of 6 K for Sr>1.5 afu to semiconducting for Sr > 1.5 afu; (4) the positions of the superlattice peaks around the (001) reflections become more incommensurate with respect to the parent structure. Rapid quenching (<5 s) from temperatures near the melting point (900 °C) can raise the superconducting Tc onset to 9 K. Independent of the cell variation with Sr content, quenching causes the c-cell dimension to expand by 0.03 Å on average while the a-cell dimension remains invariant. A small number of oxygen vacancies are quenched in from high temperature, and presumably originate in the Bi2O2 layer. As grown from the melt, crystals of the ideal 221 phase exhibit semiconducting behavior at low temperature; but with an additional high-temperature anneal in oxygen, metallic resistivity is restored with a superconducting onset near 5 K. Ca doping does not increase Tc in the ideal 221 phase. La and Y substitution occurs for Sr in the ideal 221 phase and ruins superconductivity.

Thin films of YBa2Cu3O7−x (YBCO) have been prepared on MgO substrates at 650 °C by rf-planar magnetron sputtering using a single oxide target. Depositions at two different substrate positions were examined: (A) above the inner boundary of the erosion area of a target (position A), (B) right above the center of a target (position B). The films deposited at position A suffered a serious deficiency in the contents of Ba and Cu, especially in the low gas pressure region due to the bombardment of the growing films by high-energy particles. Though we could obtain almost stoichiometric films by raising the gas pressure to 15 Pa to reduce the bombardment, high temperature annealing at 950 °C was required to improve their crystallinity and to achieve high critical temperatures (Tc). On the other hand, those deposited at position B were more excellent in crystallinity than those at position A and showed high Tc above 80 K without any annealing. Critical current density C/r) at 77 K was improved from about 103 A/cm2 to about 104 A/cm2 by annealing at low temperature of 500 °C. It is concluded that the deposition with reduced bombardment by high-energy particles enables the fabrication of high Tc YBCO films without a high temperature process.

The successful fabrication of ceramic superconducting YBa2Cu3O7−x fibers has been investigated. A new method was proposed for synthesis of the fibers through a solution route. The thermoplastic gels were synthesized using Y, Ba, Cu, ethoxides, and diethylenetriamine. The fibers were drawn from the reheated gels. The fibers were characterized by x-ray diffraction, SEM, and shrinkage ratio measurements. The fired and then annealed fiber is shown to have a superconducting transition temperature of 91 K (onset) and zero resistance temperature of 84 K. With regard to the fired fibers, it is found that the surface area increased and superconducting transition temperature decreased with increasing organic content in the initial gel. The usefulness of this method is shown and the structure of the synthesized gel is discussed.

A nucleation-and-growth mechanism for the twin formation in YBa2Cu3O7–δ superconductors based on the oxygen uptake rate curve and published transmission electron microscopic observations is proposed together with an oxygen-depleted twin boundary model. The difficulty of reaching stoichiometric YBa2Cu3O7 is explained.

We have fabricated superconducting composites composed of Y1Ba2Cu3O7–δ, copper oxide, and metallic silver. Sharp superconducting transitions were observed well above the liquid nitrogen temperature. The normal state resistivity of these composites was much lower than that of the pure ceramic Y1Ba2Cu3O7–δ. The critical current density was measured and it was comparable to that of ceramic superconductors. A substantial improvement of the mechanical properties has been achieved over those of the ceramic Y1Ba2Cu3O7–δ material.

The microstructure and the coercivity of sintered Nd20Fe(73.5-x)B6.5Alx (x = 0, 2.5) permanent magnets are influenced by the Al concentration. In Al-containing magnets we found a homogeneous distribution of Al in the hard magnetic phase and the occurrence of an intergranular Nd(Fe, Al)2, phase between the hard magnetic grains. Our analytical TEM study revealed that in “Al2O3-doped” magnets the crystal structure of the Nd-rich intergranular phase partly changes from fcc (a = 0.52 nm) to hep (a = 0.39 nm, c = 0.61 nm), whereas the content of iron simultaneously decreases from 5–10 at.% to 1.5–4 at.%. A platelet-shaped phase, embedded in the Nd-rich intergranular phase, was determined as a Nd5Fe2 (B, O)x, phase. The influence of the microstructure on the coercivity in Al-doped magnets is discussed.

The thin-film interactions of Al with refractory metals (Co, Cr, Mo, Ta, Ti, and W) have been investigated. The composition and thickness of the reacted aluminide layers were determined by Rutherford backscattering and phase identification was made by x-ray diffraction. Scanning electron microscopy was used to examine the lateral uniformity. The initial aluminide phases to grow are the Al-rich phases: Co2Al9, Cr2Al13, MoAl12, TaAl3, TiAl3, and WAI12. These are the most Al-rich phases on the phase diagrams. The reaction temperatures varied between 350 and 525 °C.

Previous qualitative studies of ion beam mixing of Ni–Ti and Fe–Ti multilayers at room temperature have shown the Ni–Ti samples to mix considerably faster than the Fe–Ti, in apparent contrast with theory. Furthermore, the Fe–Ti mixing was strongly inhibited by previous charging of the sample with hydrogen, whereas only a small effect was seen for Ni–Ti. We have quantified the mixing and extended the study to four more systems (Al–Ti. Co–Ti, Cu–Ti, and Pd–Ti) and lower temperatures. This allows some important conclusions to be drawn. Predictions based on a thermal spike model underestimate the larger room temperature mixing rates (Cu–Ti, Ni–Ti, and Pd–Ti), apparently because of contributions from a temperature dependent mechanism such as radiation enhanced diffusion. The lower mixing rates (Fe–Ti, Co–Ti, and Ni–Ti at ∼80 K) are overestimated by a factor of 2–3.5, possibly because of hydrogen contamination of the as-deposited samples. For the Al–Ti sample, the experimental mixing rate was in good agreement with predictions. Except for the Cu–Ti sample, results were seen to vary with heat of solution, rather than heat of mixing, suggesting significant contributions from the lower temperature after-spike regime. Hydrogen charging was found to reduce the Fe–Ti mixing rate by a factor of 7 at room temperature, whereas the Co–Ti and Ni–Ti rates were only reduced by a factor of 2, and the mixing of the Pd–Ti was influenced very little. Near liquid nitrogen temperature the Ni–Ti mixing rate was more strongly reduced (by a factor of 3–4). Our results suggest that the original hydrogen contamination in as-deposited samples may also cause significant reduction of mixing rates in some materials.

Films of three compound semiconductors with the zincblende structure grown epitaxially on {100} silicon substrates by chemical vapor deposition or metal-organic chemical vapor deposition were investigated by transmission electron microscopy. The three systems have similar thermal mismatches but cover a wide range of lattice mismatch. From the comparison of the observed microstructures as well as from the investigation of early stages of film formation it is concluded that the lattice mismatch plays a minor role in the formation of stacking faults and twin boundaries. A formation mechanism is proposed for these defects which is based on deposition errors during the adsorption of atoms on {111} facets of film nuclei. The observed microstructural features are discussed in terms of this model.

Phase transformations at the Si–H2O interface, induced by nanosecond pulsed laser irradiation, were studied in real time. Si samples were irradiated using a 4 ns pulse from a Q-switched frequency-doubled Nd:YAG laser while immersed in the transparent liquid. Using time-resolved conductivity and reflectivity techniques, in combination with modeling of optical parameters and heat flow, transient processes in the Si, the H2O, and at the interface have been unraveled. In the liquid, local rapid heating occurs as a result of heat flow across the interface, and formation of a low-density steam phase occurs on a nanosecond timescale. Expansion of this phase is followed by a collapse after 200 ns. These rapid phase transformations in the water initiate a shock wave with a pressure of 0.4± 0.3 kbar. Transient phase transformations and the heat flow into the water during the laser pulse influence the energy coupling into the sample, resulting in an effective laser pulse shortening. The pulse shortening and the additional heat flow into the water during solidification result in a 30% enhancement of the solidification velocity for 270 nm deep melts. Cross-section transmission electron microscopy data reveal that the Si surface is planar after irradiation and is inert to chemical reactions during irradiation. Recent experiments described in the literature concerning pulsed-laser induced synthesis at the solid-liquid interface are reviewed and discussed in the context of the fundamental phenomena presently observed.

We have developed two new etchant systems by adding H2O2 and HBr into the conventional HCI–H3PO4 etchant for the fabrication of InP-based channeled substrate heterostructure (CSBH) lasers. These etchants do not erode photoresists and they provide high quality etched side walls. The etch factors for the new etchant systems based on HBr and H2O7 are 17% and 12% higher than that of the: conventional 5HCI–H3PO4 etchant, respectively. These high etch factors give a narrow V-groove in InP and they lead to a lower magnitude and a better control of the threshold current of CSBH lasers.

Silicon dioxide for use as a diffusion barrier between soda lime glass and fluorine-doped tin oxide is deposited uniformly by atmospheric chemical vapor deposition from silane. oxygen, and nitrogen using a simple single-slot injector head. With a sufficiently thick silicon dioxide layer, the conductivity of the tin oxide is greatly improved by reducing the diffusion of sodium into the tin oxide as it is deposited between about 500 to 600 °C. Based upon the conductivity of thin lightly doped tin oxide films, it appears that at least 250 nm of silicon dioxide deposited on soda lime glass are required to essentially eliminate the diffusion of sodium into the tin oxide. However, only about 10 nm of silicon dioxide are required to obtain almost the full benefit of 250 nm thick films for moderately doped tin oxide films approximately 500 nm thick, The silicon dioxide deposition process is examined between 350 and 580 °C. The activation energy for the deposition is about 27 kJ/mole. Peak and average film deposition rates greater than 50 nm/sec and 10 nm/sec, respectively, may be obtained. The dependence of the film growth rate on the silane, oxygen, and propylene (an inhibitor) concentration is examined. The deposition rate is found to be limited by the rate of gas-phase reactions. Deposition conditions which yield high silane utilization and good film uniformity are discussed. The origin of undesirable by-product powder is studied. At low silane concentration, powder is mainly formed as the gases cool due to condensation from intermediate species.

A radio-frequency glow discharge is used for the synthesis of submicron, amorphous, silicon nitride precursor powders from silanc and ammonia. Powders are produced with a range of Si/N ratios, including stoichiometric, Si-rich, and N-rich, and contain substantial amounts of hydrogen. The powders appear to be similar to silicon diimide and are easily converted to oxide by water vapor. The powders lose weight and crystallize to a mixture of α and β–Si3N4 after prolonged heating at 1600 °C. Studies of spectrally and spatially resolved optical emission from the plasma are reported.

Silicon oxynitride films have been grown by a photochemical vapor deposition process utilizing VUV light of a deuterium lamp from a gas mixture of Si2H6, NH3, and NO2 at the substrate temperature of about 330 °C. The deposition rate of the film varied with NO2 flow rate and also with the excitation light spectrum which was varied by a low-pass filter of a synthetic or fused silica plate. The composition of the films was sensitive to the NO2 flow rate which was smaller than that of NH3 by a factor of 103.