It was demonstrated that molten Pd40.5Ni40.5P19 undergoes liquid state phase separation in the undercooling regime δT = T1 − T where T1 is the liquidus of Pd40.5Ni40.5P19 and T is the kinetic crystallization temperature. Liquid state phase separation by nucleation and growth takes place for δT ≤ 60 K while that by spinodal decomposition occurs for δT ≥ 100 K. Microstructural analysis of the undercooled specimen obtained in the undercooling regime of 60 ≤ δT ≤ 100 K indicates that it is the transition regime. Finally, it was found that when undercooled molten Pd40.5Ni40.5P19 undergoes liquid state spinodal decomposition, it first decomposes into two liquid networks, which is finally replaced by a system of three liquid networks.

Natural degradation of YBa2Cu3O7−δ powders leads to trapping of CO2 by the powder. The presence of residual carbon in ceramics or textured materials can strongly affect the superconducting properties. Optimal conditions for carbon elimination during thermal treatment are defined. Amounts of carbon lower than 500 ppm are easily obtained when thermal treatment is performed in temperature, gas flowing rate, and heating ramp conditions allowing CO2 departure before pore closure. Liquid phase formation and the presence of BaCuO2 are limiting factors. An oxycarbonate formed by reaction between this latter compound and evolved CO2 is implied in the last step of the decarbonation process.

Porosity-free nanocrystalline element selenium (nc-Se) samples with the mean grain sizes ranging from 8 to 70 nm were synthesized by complete crystallization of the melt-quenched amorphous Se solid. Mechanical properties including microhardness (Hv) and elastic modulus (E) of the nc-Se samples were measured by means of nanoindentation tests and microhardness tests, respectively. With a reduction of grain size, the nc-Se samples were found to be substantially hardened. But the grain size dependence of Hv does not follow a simple Hall–Petch relation over the whole grain size range, exhibiting three distinct stages corresponding to three different Hall–Petch slopes. The maximum Hall–Petch slope was found to be in the grain size range of 15–20 nm, corresponding to large values of the elastic modulus. This behavior can be explained in terms of the lattice distortion in the nc-Se samples that was experimentally determined by using quantitative x-ray diffraction measurements. A conclusion is drawn that the lattice structure of the nm-sized crystallites may play an important role in mechanical properties of nanocrystalline materials.

Transparent organic analogues were directionally solidified to investigate, via in situ observation the peritectic reaction occurring in the YBa2Cu3O7−x (YBCO)-superconductor system. Nucleation and growth of peritectic and properitectic phases were examined with respect to similarities with the solidification of the YBCO superconductor. The selected organic system, salicylic acid-acetamide, turned out to match the requirements concerning crystal shape, small nucleation rate of the peritectic phase on the properitectic phase, existence of stoichiometric phases with no solubility limits, and undercooling ability of the peritectic phase. Several features of YBCO growth which were previously deduced only from metallographic cross sections could be verified by direct observation. The organic analogue system will also be used in the future to improve numerical simulations.

Raman microspectroscopy (RMS) and imaging Raman microscopy (IRM) were used to probe the composition and spatial distribution of chemical phases in Bi(Pb)–Sr–Ca–Cu–O (BSCCO) ceramic superconductor powders and silver-BSCCO composites. The Raman techniques were used to identify various phases, including alkaline earth cuprates, CuO, Bi-2212, Bi-2223, and Pb-containing phases. Changes in the Ca/Sr ratios in (Ca, Sr)2CuO3 phases were distinguished by differences in orientation with respect to polarization of the exciting radiation. Variations were observed in the content and distribution of lead in various phases formed during intermediate stages of the thermal processing of composite conductors. The spatial distribution of the various phases detected in powder and composite conductors was established to a resolution of a few microns by collecting images of the Raman scattering at wavelengths corresponding to the signature peaks of the observed phases. Reference Raman spectra of the major phases observed in the BSCCO system are also reported. The Raman techniques, when combined with complementary techniques, such as x-ray diffraction and electron microscopy, can provide valuable information about the reaction paths and mechanisms of the high temperature BSCCO superconducting ceramics.

We report the results of measurements of resistivity up to 300 K and of thermoelectric power up to 400 K on ceramic samples of Nd1+xBa2−xCu3Oy with 0 ≤ x ≤ 0.65. The samples were fully oxygenated; they were characterized by x-ray diffraction and iodometric titration. The results are compared with data from literature reporting on effects of substitutions on the Ba site in 1–2–3 compounds and with our earlier experiments on substitution of Co for chain Cu. The focus is on the metal-nonmetal transition and on the nonmetallic regime in all these systems. Tc and the temperature dependence of S close to the metal-nonmetal transition and in the nonmetallic state seem to be determined by a single parameter, irrespective of the nature of the dopant. This result and its implications on the electronic structure of Rba2Cu3Oy (R = Y, or lanthanide ion) will be discussed.

Two classes of samples, designated A and B, of layered Bi–Sr–Ca–Cu oxides having the same nominal composition 4 : 3 : 3 : 4, but different thermal histories, were investigated by using field modulated microwave absorption (ESR), powder x-ray diffraction (XRD), x-ray photoelectron spectroscopy (XPS), and x-ray absorption near the edge structure (XANES). Previous electrical resistivity measurements showed that the B samples presented only two superconducting phases with midpoints of the transition temperatures at ∼80 K and ∼105 K. The microwave absorption technique indicated instead the presence of islands which became superconducting at the above-mentioned temperatures also in the A samples. The crystalline and electronic structures of the two types of samples are illustrated and discussed. A plausible theoretical interpretation of the experimental results, based on a quantum percolation model with Coulomb interaction, is also given.

Time-resolved x-ray diffraction (TRXRD) was performed during Ti5Si3 synthesis by the self-propagating high-temperature synthesis mode for different Ti size fractions. It was determined that the time for product formation (ca. 15 s) was independent of Ti particle size. However, the formation of Ti5Si4 phase occurred when relatively large titanium particles were used. A simultaneous measurement of the temperature and TRXRD allowed us to attribute the shifting of XRD peaks at high temperature to thermal expansion of the Ti5Si3 product. The thermal expansion coefficients differ for different crystal planes, and their numerical values compare well with those reported previously in the literature.

Using x-ray Rietveld analysis the fcc (fluorite-type) structure of a Na-containing nanocrystalline zirconia powder (9.5 nm estimated crystallite size) obtained by precipitation and calcination has been confirmed. The result shows that conventional x-ray diffraction techniques can distinguish the cubic crystallographic form of ZrO2 from the tetragonal one in nanosized powders. These conclusions are supported by independent Raman scattering experiments.

Thin-film heterostructures experience structural relaxation when subjected to post-deposition thermal heat treatment. The rate of relaxation, elastic effects, and inelastic effects on the stress and deformation of the structure are determined by the physical properties of the materials, in particular, the solid-phase viscosity. During relaxation, movement of defects causes an increase of viscosity with time at a constant rate as these defects are annihilated. Experimental anneals have been performed on structures with polycrystalline silicon films on (111) germanium substrates, in which the substrate relaxes during thermal annealing. A numerical analysis of the experimental results has determined values for the viscosity and viscosity rate of (111) germanium wafers. In addition, four zones of the relaxation process have been identified, and results indicate that the increasing viscosity with time has a larger effect at lower furnace ramp-up rates.

Scanning tunneling microscopy (STM) was used to characterize the surface topography of polyacrylonitrile (PAN)-based carbon fibers before and after electrochemical treatment, stretch resistance test, and high-temperature treatment. A new kind of spiral structures was found, which was not only on the surface but also in the inner layer. The spiral structure of the fibers was caused by the spinning process. The fiber structure contained the shape of the precursor. There were some large cracks in the carbon fibers after the stretching resistance test. The large cracks can result in carbon fiber breaking under certain stress conditions. The difference in the structures of the carbon fibers before and after the high-temperature treatment was determined.

Using the pulsed laser ablation (PLA) technique, conductive LaNiO3 thin films have been successfully grown on (001) Si substrates. The XRD θ-2θ scan patterns indicate a preferential (110) orientation, and the electron probe microanalyzer (EPMA) investigations show that the three elements La, Ni, and O distribute uniformly in the films. The resistivity of the as-deposited LaNiO3 films display a metallic character. Polycrystalline PbTiO3films are deposited by metalorganic chemical vapor deposition (MOCVD) on these LaNiO3 electrodes. Ferroelectricity measurements of the PbTiO3/LaNiO3 heterostructure prove LaNiO3 to be a promising electrode material in the integration of ferroelectrics and Si wafer.

Hollow nanotubes of SiO2, Al2O3, V2O5, and MoO3 have been prepared using carbon nanotubes as templates. The procedure involves coating the carbon nanotubes with tetraethylorthosilicate, aluminum isopropoxide, or vanadium pentoxide gel, followed by calcination and heating at higher temperatures in air to oxidize the carbon. SiO2 nanotubes containing transition metal ions have been prepared by this procedure since such materials may be of use in catalysis.

Decaprismatic single crystals taken from a series of alloys of nominal compositions within Al65–77Co3–22Ni3–22 have been studied by means of x-ray diffraction techniques. The substitution of Co by Ni in increasing amounts changes the (pseudo)decagonal diffraction patterns drastically and indicates structural changes which range from a single-crystalline approximant via orientationally ordered nanodomain structures and quasiperiodic phases with different types of ordering phenomena, to a basic decagonal phase. A quantum phase diagram analysis shows a clear separation of the stability regions of the ternary systems described in this study and other decagonal phases.

A Cu-rich CuInSe2 (CIS) thin film with an atomic ratio of Cu/In = 3.6 was characterized using high-resolution and analytical transmission electron microscopy (TEM). The film was deposited on a Mo coated soda-lime glass substrate by physical vapor deposition. Rutherford backscattering spectroscopy (RBS) and Auger electron spectroscopy (AES) showed that a secondary impurity phase such as Cu2Se segregated on the CIS surface. The three-dimensional crystallographic relationship between the Cu2Se and CIS was found to be (111)Cu2Se (111)CIS and [011]Cu2Se || [011]CIS where the Cu2Se and CIS had pseudocubic structures with a = 5.8 Å and a = 11.6 Å, respectively. CuPt type CIS could be observed near the interface between the Cu2Se and CIS. A growth model of CIS crystals under Cu and Se excess condition is proposed based on the results of TEM. The characteristics of the CIS growth model in Cu-rich CIS film are summarized as follows: (i) CIS crystals are produced from Cu2Se crystals by a “topotactic reaction,” and (ii) sphalerite and/or CuPt type CIS are produced first after the reaction, and (iii) the metastable sphalerite and/or CuPt type CIS is then transformed to the stable chalcopyrite CIS phase.

Directional solidification of YBa2Cu3O7 has been carried out through a Bridgman technique, and the influence of Y2BaCuO5 and CeO2 additives on the size of Y2BaCuO5 precipitates has been investigated. It is demonstrated in this work that the most efficient procedure to reduce the size of the Y2BaCuO5 precipitates is to increase the concentration of nucleation centers present in the peritectic decomposition of YBa2Cu3O7−x. A small concentration (0.3−1 wt. %) of CeO2 has a strong influence on the solidification process and on the size of Y2BaCuO5 precipitates. It is shown that when CeO2 is added, further refinement of the size of precipitates results from the formation of nanometric Y2O3 particles which further enhance the multinucleation effect. We have also observed that coarsening effects are avoided with CeO2 additives.

Mechanical alloying (MA) has been performed in the CoxCu(100-x) (x = 10, 25, 50, 60, 75, and 90) system. High resolution electron microscopy (HREM) and field emission gun transmission electron microscopy (FEG TEM) were used to characterize the microstructure and homogeneity of the nanocrystalline Co25Cu75 solid solution. After 20 h of MA, all the mixtures show an entirely face-centered cubic (fcc) phase. HREM shows that the ultrafine-grained (UFG) materials prepared by MA contain a high density of defects. Two kinds of typical defects in UFG Co25Cu75 are deformation twins and dislocations. The dislocations are mostly 60° type, and in many cases they dissociate into 30° and 90° partials. The grain boundaries are ordered in structure, curved, and slightly strained, which is similar to that observed in NC–Pd. Nanoscale energy dispersive x-ray spectroscopy (EDXS) shows that the Co concentration in both the interior of grains and the GB's is close to the global composition, which proves that supersaturated solid solutions are indeed formed. In the meantime EDXS revealed that the mixing of Co and Cu in the solid solutions is homogeneous at nanometer scale. MA in the Co–Cu system is suggested to be a diffusion-controlled process, and stress-stimulated diffusion is proposed to be the reason for the formation of supersaturated solid solutions in this immiscible system.

We report here on the synthesis of large crystals of Si-containing carbon nitride, consisting of a predominantly C–N network, by microwave CVD. The Si content in this material varies from crystal to crystal and also with the deposition conditions and has been observed to be as low as less than 5 at.% in some crystals, wherein the Si atoms are believed to substitute for some of the C sites only. This is the first time that such large and well-faceted crystals consisting almost entirely of carbon-nitride network have been synthesized. Moreover, there is no obvious deposition of amorphous CN material.

Oxygen content is a very important factor influencing the electrical properties of YBa2Cu3Oy. In this work the electrical properties of laser deposited YBa2Cu3Oy thin films on LaAlO3(100), in the whole range 6 ≤ y ≤ 7, are studied. An electrical network model, which randomly assigns oxygen contents and R(T) characteristics to the different elements in the circuit according to an arbitrary distribution, is used to analyze several features in the measured R(T) characteristics as a function of oxygen homogeneity. The model takes into account both short-range and long-range oxygen inhomogeneities. Good agreement between estimated oxygen contents from x-ray diffraction data in our samples and the average oxygen contents used to reproduce their R(T) characteristics is found.The model points out that oxygen homogeneity is very important in order to get the best and reproducible properties, and for conduction and superconductivity analysis through the shape or derivatives of R(T) characteristics.

Biaxially aligned YBa2Cu3O7−x (YBCO) films were fabricated on random Ni-based alloy tapes with yttrium stabilized-zirconia (YSZ) buffer layers deposited by ion-beam-assisted deposition (IBAD). Ar+ ion bombardment was found to have two significant effects on the crystalline structure of the YSZ buffer layers: to align a [100] axis with the substrate normal and a [111] axis with the bombarding beam axis. The resulting YSZ films were biaxially aligned on the random polycrystalline tapes, and the azimuthal distribution of the a- and b-axes of YBCO films on the top of the YSZ films was restricted to 10° FWHM. A critical current density (Jc) of 1.13 × 106 A/cm2 (77 K, 0 T) was obtained, and 1.1 × 105 A/cm2 was maintained at 5 T (77 K, B⊥c). The existence of both intrinsic and extrinsic pinning properties was clearly observed in the angular dependence of Jc with B⊥I. The longitudinal field effect on Jc was clearly observed, which indicated straight transport currents. This is evidence for strongly coupled current paths that demonstrate the bulk pinning properties of YBCO.