The ability to process large grain, uniform high temperature superconducting ceramics that exhibit high critical current densities at 77 K is essential if the enormous potential of these materials for a range of permanent magnet-type applications is to be realized. We report a study of the fabrication of large grain YBa2Cu3O7−δ by seeded peritectic solidification in which key processing parameters such as the peritectic melting process, the seed-YBCO reaction, and the YBCO solidification kinetics are investigated in detail. Evolution of the sample microstructure during various stages of the growth process, in particular, has been studied extensively. The superconducting properties of specimens cut from different regions of large grain samples have been measured using vibrating sample magnetometry, and the results correlated with the microstructure of the materials.

Macrosegregation of Y2Ba1Cu1O5 (Y211) particles was observed in Pt-added Y1Ba2Cu3O7−δ (Y123) crystals grown by an undercooling method. It was found that the macrosegregation of Y211 particles depended on the growth direction and the growth rate (R) as a function of undercooling (ΔT). The amount of Y211 particles in Y123 crystals grown at large R was larger than at small R. Also, the amount of Y211 in Y123 growing along the a-direction was larger than that along the c-direction. Further, it was noted that the smaller Y211 particles in size were distributed in Y123 grown at large R. These phenomena could be at least qualitatively explained by the prevalent trapping/pushing theory. In the direct observation of magnetic flux with the Faraday effect of iron garnet film, the flux pinning force was found to be in good agreement with the macrosegregation of Y211 particles.

Large YBa2Cu3O7−x (Y123) single crystals (larger than 13 mm cubed) have been grown along the c-axis reproducibly by the modified pulling method. The crystallinity of Y123 single crystal was investigated by x-ray diffraction and x-ray topography. Crystals grown from an MgO single crystal seed had some low angle subgrain boundaries which tilted 0.1–0.8° from each other. These grain boundaries originated from the seed crystal, and the subgrains were extended along the growth direction from the seed crystal. Y123 single crystals with no marked subgrains in the whole area were obtained by using Y123 single subgrain crystal seeds. FWHM of the x-ray rocking curve for the crystal so produced was about 0.14°, which was much better than the spectrum consisting of several separated peaks obtained from the previous crystals. Tc onset of the annealed sample was about 93.6 K, and the transition width was about 0.9 K. The low angle subgrain boundaries did not seem to be effective pinning centers for the magnetic flux.

A sol-gel process for preparing SnO2 monolith of high specific surface area and transparency from chloride solution is described. Without introducing any alkaline precipitating reagent to induce condensation, this new process employs tin chloride (or its hydrate), water, and, optionally, alcohols as the only process reagents. Spontaneous solution-to-sol and sol-to-gel transitions take place upon mixing these reagents under appropriate conditions, and the entire transition processes are carried out under acidic conditions (typically pH ≤ 4.0). The rate of condensation has been found to increase with decreasing SnCl4 concentration, which corresponds to decreasing solution acidity, and with increasing temperature. For fixed starting salt concentration and temperature, there exists an optimum amount of ethanol addition for the fastest condensation. Good performance of thus derived SnO2 monolith has been demonstrated in two applications, including catalytic oxidation and solid-state gas-sensing for carbon monoxide.

Well-crystallized polycrystalline thin films of cubic barium titanate (BaTiO3) have been synthesized on Ti-covered Si substrates by exposing the substrates to a Ba(OH)2 aqueous solution at 160 °C and a low pressure less than 1 MPa. It was presumed that the film formation of BaTiO3 involved a dissolution-crystallization mechanism, which provides an attractive approach to produce other titanate films and powders. Also, we have used for the first time this hydrothermal technique to deposit epitaxial (001)-textured PbTiO3 thin films on SrTiO3(100) substrates.

By means of dc-reactive sputtering, it is possible to vary the stoichiometry of deposited zirconium nitrides, by varying the molar fraction of N2 in an Ar–N2 gas mixture. In order to understand the origin of this effect, a theoretical model of reactive sputtering is devised. It is based on the study of reaction kinetics taking place at the surfaces of the cathode and the chamber walls. In fitting the model with experimental data, it turns out that one has to introduce the roles of Ar, N2, and N species. For reactive sputtering of ZrNz films, a good fit is obtained when it is assumed that the molar fraction of N is constant when the molar fraction of N2 increases up to about 75% (under our experimental conditions). Above this concentration of N2, the concentration of N has to increase. By the analysis of the theoretical model, general scaling laws between experimental parameters (current, pressure, and areas of the cathode and the chamber walls) are easily obtained.

The removal of binder from ceramic or metal moldings by thermolysis involves the transport of degradation products through the parent organic phase and the vacated porous body. A numerical model has been developed to combine an equation which takes into account different gas-flow regimes with an equation for the transport of organic molecules in molten polymers. Computer modeling reveals the critical heating rate above which defects occur due to boiling of the polymer-monomer solution at the center of the molding. The situation in which a porous outer layer of the molding develops, offering resistance to flow of the evolved monomer gas, is then treated. This gives rise to a moving boundary with a variable concentration of diffusant which is dependent on the surface flux, gas transport coefficient, and thickness of the porous layer. The contributions of diffusion and viscous flow to gas transport are considered.

This paper describes ZBLA fluoride glass thin films produced via an inexpensive, low-temperature reactive atmosphere sol-gel approach. Luminescence from erbium at 1.55 μm has been observed in x-ray-amorphous doped films deposited on calcium fluoride, polyimide, sapphire, and silicon substrates. Fluorescence studies of the erbium 4S3/2 → 4I13/2 transition, a characteristic emission for a reduced phonon energy host, were conducted for both sol-gel-derived films and conventionally prepared glass rods. The peak intensity observed from the sol-gel films was blue-shifted by 16 nm with a FWHM value approximately half that measured for the melt-quenched rods. Excitation studies indicate that, unlike conventionally prepared glasses, sol-gel materials suffer from nonradiative relaxation of the 4S3/2 excited state to the 4I9/2 level, where subsequent radiative emission to the 4I15/2 ground state occurs. The proposed source of the quenching mechanism are remnant species inherent to the sol-gel process. While this causes the luminescence behavior of rare-earth-doped sol-gel-derived fluoride materials to be similar to oxide hosts, these remnant species modify the branching ratios, resultantly leading to a novel 824 nm emission when excited at 488 nm.

Based on our recent experimental observations, a growth mechanism for the reactive diffusion between Si single crystal and NbC powder compact is proposed. In Si–NbC diffusion couples annealed at 1300 °C, a two-phase NbSi2 + SiC reaction layer formed with NbSi2 as the matrix and SiC as discontinuous particles. The NbSi2 grain sizes and SiC particle sizes are both in the μm range. We propose that the SiC particles nucleated at the void surfaces in the NbC powder compact. This proposed nucleation mechanism offers a potential way of controlling the SiC particle size by changing the void size and void density of the NbC powder compact. It is also pointed out that this microstructure requires Si to be the dominant diffusing species. Si must diffuse through the reaction layer, while C only has to undergo local rearrangement, and Nb need not diffuse at all.

The morphology and microstructure of an Al2O3 glass composite (trade name In-Ceram, Vita Zahnfabrik) were studied using scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The composite was produced by infiltration of a lanthanum-based glass throughout a porous Al2O3 body. This alumina body was formed by three classes of particles differing in size and shape: faceted particles typically ≤4 μm in diameter, platelets of average diameter 8 μm, 1.5 μm thickness, and small spheres 0.4 μm in diameter. The outstanding strength properties of the composite (600 MPa, ball-on-ring test) are a result of the high wetting capability of the glass phase on the Al2O3 surface. In addition, plastic strain relaxation in the faceted particles by dislocation formation compensates partially for residual stresses and impedes crack formation at the glass/Al2O3 interface.

We report the electrical bistability of C60-tetracyanoquinodimethane (TCNQ) thin films fabricated by using an ionized-cluster-beam method in a high vacuum system. The films were characterized by transmission electron microscopy and electronic absorption spectroscopy. The spectroscopic results showed evidence of the formation of the charge-transfer complex system in C60-TCNQ thin films, and the TEM results revealed the microstructure of the films. The film thickness is ∼100 nm. The electromotive intensity at the transition point was of the order of 106 V/m. The possible mechanism of the electrical phenomena of the films is discussed in the paper.

A discussion of the embrittlement of B-doped and B-free Ni3Al is given. Tensile test data and SEM fractography have been evaluated to show that additions of Pd to polycrystalline Ni3Al (B) essentially eliminate the embrittlement concomitant to charging Ni3Al (B) to the level of ∼5 wt. ppm of hydrogen.

A process for the manufacture of very thin parallel wires has been developed. A series of parallel silver wires have been written for the study of one-dimensional electron transport. The wires are approximately 200 nm wide and 8 mm long. The method used can produce longer and thinner wires.

Electromagnetic characterization and high resolution transmission electron microscopy have been conducted on the same 8° [001] symmetrical (010) tilt boundary in a naturally grown, bulk-scale bicrystal of Bi2Sr2CaCu2O8 + x (BSCCO-2212). The resistive transition showed excess resistance above and below Tc, suggesting some weak coupling at the boundary, but the inter- and intragranular voltage-current characteristics, irreversibility fields, and critical current density (Jc) values were very similar and characteristic of strongly coupled grains and grain boundary. The misorientation was accommodated by a set of partial dislocations with the Frank spacing of 1.9 nm. The dislocation cores appeared to be separated by relatively undistorted regions of crystal. The Jc, values at 25 K exceeded 103 A/cm2 in fields of several tesla, more than two orders of magnitude larger than that found earlier in [001] twist boundaries of BSCCO-2212. This result is consistent with the view that low angle [001] till boundaries play an important role for current transport in polycrystalline BSCCO tapes.

Surface microroughness of various Si(100) wafers was detected and characterized by a 180° backscattering Rayleigh–Brillouin scattering spectrometer (RBSS), and measured by an atomic force microscopy (AFM). The intensity of the scattered light from the wafers is found to increase with increasing surface microroughness which was measured by AFM. By scanning across the wafer, the inhomogeneous distribution of surface microroughness is detected and characterized. The system can be easily developed into a mapping technique. The results of the surface microroughness detected by AFM and RBSS suggest that they are complementary for the characterization of the surface microroughness from a microarea to a whole wafer.

Dislocations produced by 1300 °C indentation of the silicon-terminated (111) face of 3C-SiC were investigated by transmission electron microscopy. They were all found to be either widely separated partial dislocation pairs, or else, arrays of single partial dislocation half-loops on neighboring parallel slip planes and having the same Burgers vector. It was concluded that in the latter case, each array consisted of leading partial dislocations which had nucleated without accompanying trailing partial dislocations. The core nature of both dissociated dislocations and arrays of single partial dislocations has been determined by the technique of large angle convergent beam electron diffraction. The results indicate that the core of all single partial dislocation half-loops constituting an array consists of silicon atoms. It is concluded that, with the present deformation geometry, the Si-core partial dislocations are preferentially nucleated before the C-core partial dislocations. In the case of a dissociated dislocation, when a pair of partials was present, electron microscopy observations revealed that the morphology of the two partial dislocations was very different; while the Si-core partials were smooth, the C-core partial dislocations had a zig-zag morphology.

Transparent, conductive indium-tin oxide (ITO) and tin oxide thin films were deposited on soda-lime-silicate (SLS) float glass and silica glass substrates by an RF aerosol plasma technique in an atmospheric environment. The ITO films were deposited from solutions with various In: Sn ratios. The dependence of the film properties on the substrate temperature, deposition time, and tin concentration has been studied. The films were characterized by several techniques including XRD, EDS, electrical resistivity, SEM, optical (IR-UV-Vis transmission), Mössbauer, and infrared spectroscopy. The results showed that film phase, morphology, thickness, crystallite size, and conductivity depend on the solution composition and deposition parameters. XRD revealed that In2O3 was present in the film when a In: Sn ratio of 5: 5 or higher was used; otherwise only SnO2 shown. SEM analysis showed that dense and uniform films were formed with particle sizes ranging from approximately 50 nm to 150 nm. The resistivity of the ITO films ranged from 0.12 to 5.0 ohm-cm at room temperature. Optical transmission of the ITO-coated glasses was not different from the uncoated samples. Infrared results indicated that the structure of the near surface of the glasses was significantly modified with a higher indium concentration. The advantages of the atmospheric, RF aerosol plasma deposition process over other techniques are discussed.

The formation processes of epitaxial nickel silicides, resulting from the interaction of nickel silicide films (10 nm–100 nm) on (111) silicon (Si) substrates after furnace annealing, have been studied using transmission electron microscopy (TEM) and x-ray diffraction (XRD) techniques. The formation of type-A epitaxial grains (i.e., grown with the same orientation of the underlying Si substrate) and type-B epitaxial grains (i.e., rotated by 180± around the surface normal) in “thick” epitaxial films (i.e., greater than 35 nm) is proposed to be linked to the formation of a fluorite-based CuPt (L11)-like NiSi phase. This phase is found to be a metastable phase and is believed to be a transitional phase toward the formation of the equilibrium NiSi2 phase in both type-A and type-B orientations. In addition, we have found that a fluorite-based CuPt-like NiSi may even coexist with a fluorite-based CuAu I-like structure. The interrelationship between these two structures is discussed in the context of a displacive transformation process in fcc structures as originally proposed by Hansson and Barnes [Acta Metall. 12, 315 (1964)] and Pashley et al. [Philos. Mag. 19, 83 (1969)].

A Pd–Si–Cu bulk nanocrystalline material was prepared by quenching the melted Pd78Si16Cu6 alloy at a cooling rate of 200 K/s under 2–6 GPa. It was found that the nanocrystalline material consists of Pd(Cu) disordered solid solution and a metastable phase-II, Pd4Si. The grain size was found to decrease with increasing pressure. The influence of high pressure on the grain size of bulk nanocrystalline material is discussed, and a possible formation mechanism is proposed.

The coprecipitation technique has been used to prepare ZrO2 (Y2O3 3 mol %) nanopowder. The influence of residual NH4Cl and pH value on the crystallization of ZrO2 (Y2O3 3 mol %) nanopowder have been investigated by differential scanning calorimetry (DSC), thermogravimetric analysis (TGA), x-ray diffraction (XRD), infrared spectrometry (IR), and transmission electron microscopy (TEM) techniques. The IR spectra proved that the presence of residual NH4Cl increased the amount of the hydroxo group. This led to serious gel agglomerate and free enthalpy decrease. Therefore, the crystallization of ZrO2 (Y2O3 3 mol%) nanopowder is greatly influenced by the residual NH4Cl. While there is no residual NH4Cl, the crystallization takes place at 445 °C and is an exothermic process. On the contrary, with NH4Cl the crystallization takes place at 376 °C and is an endothermic process. However, the pH value does not influence the crystallization of ZrO2 (Y2O3 3 mol%) nanopowder.