We first measured the thermoelectric properties of layer-structured homologous compounds, (ZnO)mIn2O3 (m = integer), and reported that they would becomecandidate materials for high-temperature thermoelectric energy conversion.1–4 We further tried to improve their thermoelectric properties by partially substituting yttrium for indium in (ZnO)5In2O3. Though the ionic radius of Y3+ is larger than that of In3+, the a-axis (hexagonal system) elongated and c-axis shrank as Y was substituted for In. The thermoelectric properties were found to vary with a varying amount of Y substitution; 3% Y substitution gave rise to the largest thermoelectric figure of merit, i.e., 1.1 - 1.3 × 10-4 K-1 at 960–1100 K. The abnormal change in the lattice structure by Y substitution was responsible for the unusual behavior of the thermoelectric properties.

The CHF3 electron cyclotron resonance (ECR) plasma etched LiNbO3 (LN) surface was analyzed chemically and crystallographically to investigate the dry-etch machining process for LN crystal, which was recently needed to obtain broader-band optical modulators. The etched surface was entirely covered with amorphous-like precipitates having ~70 nm diameter. These precipitates (or a part of them) were thought to be LiF from Auger electron and x-ray photoelectron spectroscopy. The results indicated that the LiF was formed and remained on the etched surface while the Nb was almost completely removed.

Production problems attributed to excessive stresses generated during the cure of epoxies led us to develop a formalism to predict these stresses. In our first studies, we developed a fundamental understanding of the complex evolution of viscoelasticity as the cure progresses. We then incorporated these results into a proper tensorial constitutive equation that was integrated into our finite element codes and validated using more complicated geometries, thermal histories, and strain profiles. The formalism was then applied to the original production problem to determine cure schedules that would minimize stress generation during cure. During the pursuit of these activities, several interesting and puzzling phenomena were discovered that have stimulated further investigation.

The evolution of surface structure, grain microstructure, and superconducting transition temperature of a-axis YBa2Cu3O7 thin films has been studied as a function of film thickness. The grain size increases and develops a bimodal distribution of grain size during film growth, concurrent with an improvement in Tc. The surface structure does not represent the grain size, but rather the development of the bimodal grain structure follows the formation of the surface structure. The results are discussed in terms of thin film growth modes.

Superconducting HgBa2CaCu2O6+δ (Hg-1212) thin films have been prepared by laser ablation followed by post-annealing at high temperatures. Two synthesis methods were investigated, using (1) direct reaction of Hg–Ba–Ca–Cu–O precursor films in a Hg-controlled ambience, and (2) thermal diffusion of Hg into Ba–Ca–Cu–O precursor films in a controlled atmosphere containing both Hg- and Tl-bearing species. Effects of the annealing temperature, time, and bulk material composition on the Hg-1212 film and residual impurities are presented. Surface morphologies, growth defects, and transport properties of Hg-1212 on SrTiO3 substrates are discussed. Formation of Hg-1212 films on MgO and LaAlO3 substrates is briefly described.

A new quenching technique was used for detailed microstructural examination of quenched YBa2Cu3O6+δ/liquid interfaces. The examination revealed that the growth rate and the amount of excess Y2BaCuO5 (211) had a strong influence on the growth morphology of YBa2Cu3O6+δ (123). The maximum growth rate at which single crystal growth could be obtained increased from 1 μm/s to 1.5 μm/s as excess 211 content increased from 0 to 20 wt. %. It then decreased to 1 μm/s as excess 211 increased to 40 wt. %. Dendritic growth with distinguishable secondary arms occurred for stoichiometric 123 samples in the regime of cellular/dendritic growth. A highly curved 123 envelope was formed on 211 particles located at the 123 growth interface for stoichiometric 123 samples in the regime of single crystal growth. The microscopic 123 growth interface became flat as excess 211 content increased to 20 wt. %. The engulfment of 211 particles into 123 matrix is discussed based on detailed microstructural examination. It is found that the formation of a small highly curved 123 envelope on 211 particles for stoichiometric 123 samples is due to the large 211 particle spacing.

High-temperature x-ray diffraction measurements of a (Bi, Pb)-2223 precursor mixture used to produce high-Jc superconducting tapes were conducted on silver and ZrO2 substrates. The precursor mixture consisted primarily of 2212, Ca2PbO4, and CuO. Phase evolution was markedly sensitive to oxygen partial pressure: In 10% O2 growth of the 2223 phase on silver was rapid, proceeded at the expense of the 2212 phase, and was preceded by the disappearance of the Ca2PbO4 phase. When slowly heated on a silver substrate in 7.5% O2 the 2212 phase melted near 800 °C and subsequently recrystallized near 820 °C in a highly textured form, but with no detectable 2223 formation. Under similar conditions on a ZrO2 substrate, the mixture exhibited no marked changes in the XRD patterns up to 850 °C. The dramatic reactivity on silver was also highly dependent on heating rate; rapid heating in 7.5% O2 to 825 °C did not result in melting of the 2212 phase or appearance of the 2223 phase. In experiments leading to formation of 2223, the c-lattice parameter of the 2212 phase contracted just prior to the onset of formation of 2223. This result is consistent with the formation of an intermediate Pb-doped phase of 2212. A transient amorphous phase appeared briefly at the onset of formation of 2223. No evidence for intergrowth conversion of 2212 to 2223 was observed.

When a melt of BaO and CuO mixture was infiltrated into sintered Y2BaCuO5(211) compact to form YBa2Cu3Ox(123) superconductor, butterfly-like plane patterns of 211-free regions were observed to form within growing 123 grains. In a 123 grain, the 211-free region was found to be a pair of vertex-shared pyramids and 211 entrapped region to be the rest of the bulk of the grain. An observation of patterns and cracks formed within 123 grains revealed the base of the pyramids to be (001) plane. The difference in entrapment, which depends on crystallographic planes and results in the formation of the pattern, was explained by the dihedral angles between 123 and 211. The dihedral angle between a - (or b-) plane and 211, which is believed to be greater than zero degree, might cause the entrapment of 211 particles in a [100] (or [010]) direction. In contrast, the dihedral angle of most probably zero degree between c-plane and 211 inhibited the entrapment. The observed shape of 211 particles in front of a-(or b-) and c-planes supports the above explanation of 211 entrapment to form the butterfly-like patterns. was explained by the dihedral angles between 123 and 211. The dihedral angle between a- (or b-) plane and 211, which is believed to be greater than zero degree, might cause the entrapment of 211 particles in a [100] (or [010[) direction. In contrast, the dihedral angle of most probably zero degree between c-plane and 211 inhibited the entrapment. The observed shape of 211 particles in front of a-(or b-) and c-planes supports the above explanation of 211 entrapment to form the butterfly-like patterns.

(Bi, Pb)2Sr2Ca2Cu3Ox (2223) single crystals have been grown using a fused-salt reaction of Bi2O3, PbO, SrCl2, CaCl2, CuCl, and KNO3 in a KCl flux. The pristine crystals show regular plate-like morphology with typical dimension of 0.1 × 0.1 × 0.001–0.01 mm3. Crystal orientation, chemical composition, phase purity, and superconductivity of the pristine crystals were determined by SEM, TEM, EDX, x-ray diffraction techniques, and SQUID magnetometry. The relative fraction of the Bi-2223 phase (Tc = 110 K) in as-grown crystals is ~97%. The only impurity phase, Bi-2212, occurs in some selected crystals but is present in amounts less than the detection limit of x-ray diffraction and is unobserved in the diamagnetic signal determined by SQUID magnetometry.

Diamond was deposited at 850 °C by microwave plasma chemical vapor deposition (CVD) on the interlayers with various intensity ratios (ID/IG) of the D band (~1400 cm-1) to the G band (~1570 cm-1) in the Raman spectra. Diamond could be grown only on the interlayers with higher ID/IG (≤1.95), and Nd was slightly increased to 3 × 106/cm2with ID/IG. The predeposition at 350 °C, which decreased the full-width at half-maximum of the broad D band, further increased Nd to 5 × 107/cm2. With 300 ÅA Pt overlayer on the interlayer, Nd was much more enhanced to 8 × 107/cm2. We suggest the sp3 bonded carbon clusters within the interlayer contribute to diamond nucleation, but they should be survived against atomic hydrogen etching during diamond deposition by increasing the sp3/sp2 ratio, by increasing the degree in clustering, or by protecting them with overlayer.

In this paper, nanometer-sized CdO organosol was prepared by using microemulsion methods. Its electronic structure and optical properties are characterized through UV-visible light absorption, photoluminescence, and Z-scan techniques. Some newfeatures were observed. Fluorescence and nonlinear optical responses are mainly related to surface trapped states.

The nature of dissociated superlattice dislocation cores in Al66Ti25Cr9, deformed at room temperature, has been characterized by weak-beam transmission electron microscopy (TEM) and comparison of experimental images with computer-simulated images. The displacement fields associated with narrowly dissociated APB- and SISF-dissociated ‹110› superdislocations were calculated to account for the asymmetry in dislocation contrast and led to a better understanding of the formation of images. Such calculations are a powerful aid, when coupled with image simulations, in distinguishing the “real” intensity peaks from the supplementary peaks that can be generated under experimental imaging conditions. While both APB- and SISF-dissociated superdislocations were identified, the vast majority of superdislocations were determined to be APB-dissociated. Corrected values of the fault energies (γAPB and γSISF ) have been measured for this alloy. These energies and the observed dissociations are shown to be self-consistent.

A γ-based TiAl alloy with equiaxed microstructure and fine grain size has been studied to analyze the deformation mechanisms responsible for the creep behavior. The microstructures produced by creep and high temperature deformation have been examined by TEM to obtain information about the different aspects characterizing the primary and secondary stages of creep. Mechanical twinning has been confirmed to occur in a fraction of the grains that never exceeds 50% while 1/2 ‹110› dislocations are active within all the γ grains. The twins are only responsible for a small amount of strain, but they lead to a subdivision of the microstructure and determine (directly or indirectly) the hardening process observed during the primary stage of creep. We have proposed that during the secondary stage the creep rate is determined by the unblocking of pinned dislocations by processes such as a pipe diffusion or cross slip that allow thermally activated glide of 1/2‹110› dislocations on (001) planes.

Superplastic behavior of aluminum matrix composites with discontinuous reinforcements has been investigated in a temperature range below the melting temperature measured by differential scanning calorimetry. The experimental results of the mechanical properties revealed that the rate-controlling process of superplastic flow was associated with dislocation movement controlled by lattice self-diffusion. The strengthening due to the presence of reinforcements was retained. It is suggested that the strongest strengthening process of the dislocation-pileup mechanism and the diffusional relaxation-limitation or dislocation bypass mechanism affects the rate-controlling process.

The hydrothermal growth of epitaxial BaTiO3 thin films on single-crystal SrTiO3 substrates occurs by the island growth mode. The aqueous solution chemistry is found to control interfacial characteristics and plays an important role in controlling film formation and faceting. Island faceting can be changed by the introduction of additional cations during synthesis. Electrophoretic data, confirmed by adsorption measurements, show that barium is a potential determining counterion and adsorbs on SrTiO3 surfaces. Initial electrical measurements show that the BaTiO3 films have a dielectric constant of 141 with a loss tangent of 0.9 that decreases with heat treatment.

Donor-doped BaTiO3 ceramics were prepared by adding PbO B2O3 SiO2 as a sintering aid. Semiconducting BaTiO3 was obtained at a sintering temperature of 1100 °C. The sintered samples exhibit the Positive Temperature Coefficient of Resistivity (PTCR) effect, which depends on the amount of liquid phase, the concentration of the donor-dopant, and the sintering temperature. The cold resistivity of the samples decreases when the sintering temperature increases. The increase of the grain boundary resistivity and hence of the cold resistivity at lower sintering temperatures was explained by applying the diffusion grain boundary layer model.

The preparation of thin (ca. 200 μm) Ce0.9Gd0.1O1.95 planar electrolytes using the tape rolling technique is described. The processing and formation of these electrolytes involved several steps: (i) the production of a processable ceramic paste, (ii) rolling and cutting, (iii) binder burnout, and (iv) sintering. The rheology of these ceramic pastes is characterized by a hardness indentation test. The materials parameters which may be obtained from the hardness indentation test such as the hardness (plastic flow stress), elastic modulus, and plasticity index are provided. The rheology, as characterized by the hardness method, of the pastes is shown to be influenced by the nature and extent of processing aids and also the mixing and milling times. Further, it is shown that by using a paste formulation with appropriate rheological properties, it is possible to produce uniform thin green tapes using a twin roll mill. The binder burnout characteristics of the ceramic pastes were studied by using a specially constructed thermal gravimetric apparatus. It is shown that the heating rate and the ambient atmosphere have strong influences upon the binder burnout kinetics of these green tapes. Finally, it is shown that sintered Ce0.9Gd0.1O1.9 electrolytes, with a near theoretical density and with a uniform microstructure as well as a chosen near net shape, may be prepared from the corresponding tape rolled greens.

The initial dielectric aging behaviors of a Mg and Mn doped lead magnesium niobate ceramic were investigated over a wide range of direct current (dc) bias. Both the dielectric constant-log(time) and the loss tangent-log(time) were regressed in terms of a linear relationship. The dc bias is found to have a strong influence on the dielectric parameters at the start of aging and to suppress the aging of dielectric constant and loss tangent. The frequency dependence of the dielectric aging is also evidently affected by the dc bias.

A combustion synthesis (SHS) process developed in our previous study for the synthesis of Si3N4 has been tested for the synthesis of boron nitride (BN) powder. Boron and NaN3 powders were used as the reactants. In addition to ammonium halides, KHF2, FeCl3, NaNH2, or a mixture of 50 mol% FeCl3 and 50 mol% NaNH2 was added to the reactants to examine their catalytic effect. These powders were mixed and pressed into a cylindrical compact. The compact was wrapped up with an igniting agent (i.e., Mg + Fe3O4) and the synthesis reaction was triggered by the combustion of the igniting agent. It was found that only those reagents containing both halogen and hydrogen can exert effectively the catalytic effect. The BN powder as-synthesized is mostly in the form of agglomerated fine particles (0.1–1 μm in diameter) and is hexagonal in crystalline structure. Effects of various experimental parameters on the product yield were investigated. A possible reaction mechanism was proposed, which explains the effects of the experimental parameters on the synthesis reaction.

A nonfluorinated β-diketonate precursor, bis(t-butylacetoacetato)Cu(II) or Cu(tbaoac)2, was synthesized by modifying bis(dipivaloylmethanato)Cu(II) or Cu(dpm)2 for chemical vapor deposition (CVD) of copper. The complex was characterized by a variety of techniques, such as melting point determination, mass spectrometry, infraredspectroscopy, elemental analysis, thermogravimetric and differential thermal analysis, and x-ray diffraction. Cu(tbaoac)2 has a higher sublimation rate than Cu(dpm)2 over the temperature range 90–150 °C. Pyrolysis of Cu(tbaoac)2 leads to the formation of copper films at 225 °C, compared to 330 °C for Cu(dpm)2. As-deposited copper films ere highly dense, mirror-bright, adhered strongly to SiO2, and showed a resistivity of less than 2.9 μΩ-cm at a thickness as low as 1300 Å. A possible mechanism for the decomposition of the ligand tbaoac has been proposed.