Bismuth-based high Tc superconductors have been prepared as fibers by a technique of melt extraction. As-made, the fibers are amorphous with diameters ranging from 0.7 μm to 100 μm and lengths of up to 5 cm. The fibers were subsequently transformed into high Tc superconductors by heat treatment in air. Superconducting transitions at 105 K and 82 K were measured in annealed fibers of initial composition Bi1.8Pb0.2Sr2Ca3Cu4Ox by SQUID magnetometry. The volume fractions of superconducting phases were estimated to have lower bounds of 30% for 2212 and 5% for 2223. The crystallization process has been studied by differential scanning calorimetry, electron microscopy, and x-ray diffraction. Crystallization involves first the formation of the Bi-2201 phase and a bcc phase with lattice parameter a = 0.425 nm before finally significant fractions of both the Bi-2212 and Bi-2223 phases are formed.

Rapidly solidified Al78Mn20Ge2 alloy exhibits a curious structural feature; this corresponds to the simultaneous occurrence of almost all the quasicrystalline phases, e.g., primitive and face-centered icosahedral phase, rational approximant, and a new metastable cubic phase. The cubic crystalline phase shows yet another type of recently observed twin relation which effectively produces an icosahedral symmetry, a feature that has so far been specific to alloy systems Al–Mn–Si and Al–Mn–Fe–Si only. The diffraction evidences obtained in the present investigation reveal that the orientation of the structural subunit, which is a MacKay icosahedron, remains invariant across the various interphase boundaries. These results elucidate clearly the structural interrelationship among the various phases.

We have studied the effects of temperature (10 ≤ T ≤ 295 K) and pressure (0 ≤ p ≤ 0.8 GPa) on the state of intercalate layer crystallization in SbCl5 graphite intercalation compounds of stages 2, 4, and 8. At room temperature (RT), the intercalate layer may in some second stage compounds be fully crystallized and lowering the temperature creates no further modifications. In all other cases, i.e., those in which the intercalate layer has only partial crystallization at RT, lowering T leads to the formation of new in-plane unit cells, the final state depending on the kinetics. Applying pressure to above 0.3–0.5 GPa results in crystallization in all cases, different from that induced simply by lowering of the temperature. We discuss the unit cells observed and the relationships they bear to each other in the light of other works on similar compounds.

Hydrogen implanted into ceramic YBa2Cu3O7−x (YBCO) with a dose of 1 × 1017 H+ cm−2 started to effuse as molecular hydrogen from the YBCO to atmosphere at a temperature of 200 °C, effuse predominantly as water by reacting with oxygen at temperatures of 300–700 °C, and again effuse as molecular hydrogen at temperatures above 800 °C. The improvement of the superconducting properties of the proton implanted YBCO occurred at annealing temperatures for which implanted hydrogen effused predominantly as water by reacting with oxygen.

Copper and lead powders were precipitated by laser-induced reduction of copper(II) formate, copper(II) acetate, and lead(II) acetate dispersed/dissolved in glycerine by exposure to 248 nm KrF pulsed laser radiation. The deposited powders consisted of pure copper and a mixture of pure lead and partially reduced metallo-organic complexes, respectively. The reduction of the metallo-organic complex of lead was completed thermally. Temperature, concentration, laser pulse repetition rate, and stirring influenced the deposition rate in both cases. The copper particles were predominantly hexagonal in shape and ranged in size from 0.01–0.04 μm. The lead particles were football shaped and had a very narrow size distribution, with an axial dimension of about 0.5 μm. It was shown from a spectroscopic analysis of the reaction products that the initial nucleation was caused by photochemical processes. However, exposure of the nonaqueous solutions to CO2 laser pulses at room temperature did not yield any particles.

Modulated microwave absorption measurements at 9.3 GHz were made on the low field absorption observed in the superconducting phase of Bi–Sr–Ca–Cu–O. The line intensity observed with a low modulation amplitude of 50 mOe showed a maximum between 70 K and 80 K and dropped to zero near 95 K. With a modulation amplitude of 10 Oe, an additional broad line absorption was observed above 88 K, peaking in intensity near 95 K, and disappearing above 100 K. Hysteresis, associated with flux trapping, occurred when the maximum field Hmax in a sweep cycle exceeded a critical value H*(T), which varied from about 7 Oe at 59 K to 1 Oe at 82 K. For Hmax > H*, the hysteresis splitting at first varied linearly with (Hmax – H*), later saturating at a value δHmax(T). Above 70 K, the relationship δHmax = b(T0 – T) was obeyed with T0 = 92.3 K and b· = −0.3 Oe/K for H perpendicular and b· = −0.23 Oe/K for H parallel to the c-axis.

Aging experiments were conducted to study initial state Fe-clustering in Au–Fe alloys with Fe content from 10.7 to 33%. Information derived from experiments using transmission electron microscopy, electron diffraction, and high resolution electron microscopy suggests the coexistence of short-range-order and Fe-clusters. At early stages of aging, lobe-like and/or rod-shaped strain contrast images, identified as clusters, were revealed after specimens were further cleaned by an ion-miller. The (11/20) special point diffuse reflections were prominent in the as-quenched condition and/or early stage aging, and the intensities decrease gradually as aging proceeds. After a certain period, (11/20) diffuse reflections disappear but strain contrast images still remain similar. This suggests that the strain contrast images are not related to the (11/20) diffuse reflections. The cluster characteristics of Au–Fe alloys are differentiated from those of Al–Cu and Cu–Be based upon theoretical calculations.

Diamond crystallites and thin films have been deposited onto polycrystalline aluminum substrates utilizing an electron cyclotron resonance microwave plasma-assisted chemical vapor deposition (ECR-PACVD) method. For all depositions, the substrates were biased to +40 V dc with respect to ground and their temperature was maintained at 500 °C. Similar deposits were obtained from two different feedgas systems at a total pressure of 1.33 Pa (10 mTorr). The first system consisted of a carbon monoxide (CO) and hydrogen (H2) mixture (CO:H2 = 20:80), and the second was a methane (CH4), oxygen (O2), and hydrogen (H2) mixture (CH4:O2:H2 = 21:10:69). The deposits were subsequently characterized by scanning electron microscopy, micro-Raman spectroscopy, and x-ray diffraction. The results of these analyses indicate that polycrystalline diamond was deposited onto aluminum substrates, as both individual crystallites and continuous films.

Thick Bi2Sr2CaCu2O8 films have been produced by melting Bi2Sr2CaCu2O8 powder on MgO substrates at temperatures just above the melting temperature of the powder. X-ray diffraction measurements indicate enhanced c-axis alignment throughout the thickness of the films. Films melted at 900 °C show greater alignment and contain less Bi2Sr2CuO6 compared to those processed at 950 °C. Both the degree of alignment and the Bi2Sr2CuO6 content increase as the cooling rate is decreased. Transport measurements show that films quickly cooled from low melt-processing temperatures have the highest critical current densities (Jc = 13 kA/cm2 at 30 K). The temperature dependence of Jc is best described by a flux creep model. Finally, Jc at 4.2 K (in both parallel and perpendicular magnetic fields) undergoes a sudden drop at low fields, but levels off above 0.5 T to about 30% of the zero field value.

Elemental Fe and Sn powders in the ratio of 1:2 were ball-milled for various times at room temperature, and phase transformations in the powders were studied by 57Fe and 119Sn Mössbauer spectrometries, transmission electron microscopy, and x-ray diffractometry. Although Fe-Sn alloys are not obvious candidates for solid-state amorphization reactions, an amorphous phase formed after only a few hours of ball milling. Nanocrystalline intermetallic FeSn2 particles nucleated and grew within the amorphous phase, and FeSn2 became the major phase after 10–20 h of ball milling. These small particles were superparamagnetic, and were above the blocking temperature at room temperature.

Previous studies of a single lot of NiAl powder which had been ground under high intensity conditions in liquid nitrogen (cryomilling) indicated that this processing leads to a high strength, elevated temperature NiAl–AlN composite. Because this was the first known example of the use of the reaction milling process to produce a high temperature composite, the reproducibility of this technique was unknown. Two additional lots of NiAl powder and a lot of a Zr-doped NiAl powder have been cryomilled, and analyses indicate that AlN was formed within a NiAl matrix in all three cases. Compression testing between 1200 K and 1400 K has shown that the deformation resistance of these heats is similar to that of the first lot of NiAl–AlN; thus cryomilling can improve the creep resistance of NiAl by a factor of six. Based on this work, it is concluded that cryomilling of NiAl powder to form high temperature, high strength NiAl–AlN composites is a reproducible process.

YBCO was synthesized using atomically mixed nitrate precursors. Atomic mixing was achieved using a freeze-dried process which is fully discussed here. The thermal processing behavior of these precursors is fundamentally different from that of mechanical mixtures of the Y, Ba, and Cu oxides and it is examined in detail. Ba2Cu3O5+x (normally considered a high oxygen pressure phase) and Y2O3 formed as nitrate decomposition products at ambient atmospheric conditions. Subsequent reaction of these materials (2 h at 925 °C) produced polycrystalline YBCO. Without any post-processing of the powders, product YBCO powders consisted of 30 μm agglomerates composed of crystals 1–3 μm on an edge. The powdered products exhibited a magnetic susceptibility greater than 90% – 1/4π.

The nucleation and growth of quasicrystalline thin films during sequential vapor deposition of aluminum and manganese on various substrates have been studied at temperatures between 530 and 650 K. The films were analyzed by transmission electron microscopy, electron diffraction, energy dispersive x-ray analysis, replica techniques, and Auger depth profiling. The quasicrystalline phase is identified as icosahedral. It nucleates on the surfaces of the Al films. There is no indication of substantial bulk Mn diffusion. The growth process is governed by diffusion of Al to the quasicrystal surface where it reacts with the incident Mn.

A detailed study of the crystallization process for compositions near Bi2Sr2Ca1Cu2Oy was undertaken using differential thermal analysis (DTA), transmission and scanning electron microscopy (TEM and SEM), and x-ray diffraction (XRD). Glasses prepared by a splat-quench technique were free of secondary phases in most cases. A two-step crystallization process in oxygen was observed in which partial crystallization of the glass occurs initially with the nucleation of “2201” and Cu2O, and is completed with the formation of SrO, CaO, and Bi2Sr3−xCaxOy. No specific thermal event could be associated with the formation of the “2212” phase. Rather, formation occurs via conversion of 2201 into 2212. This was a kinetically limited process at temperatures below 800 °C as other phases were found to evolve in addition to the 2212 phase during extended anneals. In contrast, a nearly full conversion to the 2212 phase occurred after only 1 min of annealing at 800 °C and above. However, changes in resistivity data, secondary phases, and the measured 2212 composition upon extended anneals at 865 °C showed that considerably longer heat treatments were necessary for the sample to reach its equilibrium state.

A series of samples along the composition lines Bi2+xSr2−xCuOy, and Bi2Sr2−xCuOy have been used to study the structural modulation, chemistry, and superconducting properties of pseudo-tetragonal Bi2Sr2CuO6 (2201). The 2201 phase can be formed from crystallization of thin glassy platelets. The sample displayed a strong crystallographic (00l) orientation which made it possible to determine incommensurate modulations near (00l) reflections using a conventional x-ray θ-2θ scan. From the crystallization of the 2201 phase, it was found that structural modulation was intrinsic to the phase, and ordering of the structure required a long time at high temperature. High temperature in situ x-ray diffraction of a 2201 Bi2Sr1.85CuOy platelet showed that the modulation existed at 875 °C in O2 (Tmelt ≍ 892 °C in O2). These suggest that the structural modulation cannot be caused solely by oxygen ordering and that metal-ion displacement must be involved. By removing 0.04 to 0.05 oxygen atom per formula unit from Bi2Sr2CuOy and Bi2Sr1.85CuOy, the c* components of the modulation changed from 0.31 to 0.26 and from 0.38 to 0.31, respectively, while the b* component of the modulation remained approximately 0.2. This demonstrates that oxygen, while not the sole cause, does play a role in the formation of the structural modulation. However, the invariance of bmod with respect to the change in oxygen content does not support the model that explained the modulation by inserting extra oxygen in the BiO plane. By varying metal-ion concentrations of Bi and Sr we found that both the lattice parameters and the modulation vectors depended more on the Bi/Sr ratio than on the Sr concentration alone. As the Bi/Sr ratio increased from 1.0 to 1.35, the modulation lines moved toward the (00l) reflections. The corresponding superstructural periodicities were calculated to vary from ∼1/5b* + 0.32 c* to ∼1/5 b* + 0.63 c*. Effects of oxygen content and metal-ion concentration on the 2201 phase formation and the superconducting properties will also be discussed.

We present experimental data for the c-axis resistivity ρc of stage s = 2, 3, 4, 5, and 8, SbCl5 intercalated graphite, over the temperature range 40 to 300 K and the pressure range 0 to 0.8 GPa (0–8 kbar). For most specimens studied, resistance anomalies are observed below 230 K at atmospheric pressure and at pressures up to 0.5 GPa at 293 K. These anomalies are explained in terms of structural changes from a disordered or partly crystallized in-plane intercalate structure at atmospheric pressure and T > 230 K to an almost completely crystallized structure below this temperature, or at elevated pressures, as discussed in a companion paper. In the crystallized phases ρc is approximately linear in T except for stage 8, for which a nonlinear behavior, with a negative temperature coefficient of resistivity below 200 K, is observed. The results are compared with previously available literature data, and the p-T phase diagram is briefly discussed.

We report on 27Ai, 65Cu, and 51V spin-echo spectra for the amorphous phase and icosahedral quasicrystal of the Al75Cu15V10 alloy, and 27Al, 65Cu, and 55Mn spin-echo spectra for the icosahedral and crystalline phases of the Al67Cu20Mn13 alloy. The line shape and peak shift reveal different local characteristics among those phases. For the Al75Cu15V10 alloy, peak shifts of all constituent nuclei are more positive in the amorphous phase than in the icosahedral phase, indicating a different s-electron density. For the Al67Cu20Mn13 alloy, an as-quenched icosahedral phase transforms to a crystalline phase by heat treatment. Different peak shifts of 27Al and 55Mn except 65Cu between those phases have been found. It is suggested that there are Mn atoms carrying magnetic moment and that there is no difference in the electronic structure of Cu atoms between those phases.

Combustion synthesis of elemental powder compacts has been used to produce alloys with compositions corresponding to Al3Ti, Al73Ti24Cr3, and Al67Ti25Cr8. The binary composition exhibits a strong exothermic reaction at ∼665 °C, resulting in formation of single phase Al3Ti with the tetragonal DO22 structure. The heat of formation of the compound at 298 K, δHf(298), was estimated from peak reaction temperature measurements to be −35.0 kJ mol−1. Additions of Cr lowered the reaction initiation temperature and resulted in the formation of intermediate products attributed to Al–Cr reactions. The DO22 structure remained the primary reaction product in Cr-containing alloys. The Cr particles did not completely dissolve during initial reaction; an additional heat treatment at 1200 °C or above was required to homogenize the material, resulting in partial or complete transformation of the DO22 structure to the cubic L12 structure, depending upon Cr content. Homogenization at 1250 °C for 4 h produced material consisting approximately of a 50-50% mixture of the DO22 and L12 structures for Al73Ti24Cr3, and 100% L12 for Al67Ti25Cr8. In all cases, reaction at ambient pressure was accompanied by swelling, resulting in final densities less than 60% of theoretical. Application of external pressure, either during or subsequent to combustion synthesis, produced near theoretical density materials exhibiting a homogeneous and equiaxed microstructure.

Nuclear microscopy combines a range of MeV light ion beam analytical techniques such as Proton Induced X-ray Emission (PIXE), Rutherford Backscattering Spectrometry (RBS), and Scanning Transmission Ion Microscopy (STIM). One of the main advantages of using MeV light ion beams for materials characterization is the large analytical volume due to their high penetration depth. This paper shows how nuclear microscopy is used to determine the size and distribution of Pb precipitates in a 40 μm thick alloy sample with a nominal composition of Al–5 wt.% Pb.

Exoelectron emission from the surface of unexcited metallic glasses Fe78B13Si9 during heat treatment has been studied under ultra high vacuum condition. In the first heating cycle, exoelectrons are emitted from the as-cast ribbon in the temperature range from approximately 423 K to 773 K (150 °C to 500 °C), although the surface of the specimen is not excited by ionizing radiation, chemical processes, or mechanical treatments prior to measurements. In the second and subsequent heating cycles, however, there is no anomalous emission observed in the same temperature range. In order to elucidate the mechanism of emission, the surface of the specimen is observed by the atomic force microscope (AFM) before and after measurements. In the AFM image, many crystallites in the amorphous matrix can be found in the surface of the heated specimen. These experimental results show that exoelectrons are emitted in the same temperature range as the early stages of crystallization on the surface of metallic glasses. We hypothesize that the two effects are correlated.