A new form of transparent condensed nanophase material of GaN was synthesized directly by ammono-thermal synthetic route. Nano-sized effects and thermal stability of that material were investigated through Raman scattering and infrared spectra. Compared with bulk GaN, we observed the Raman low-energy-shift of the phonon frequency of E2(high) and the transverse optical mode [E1(TO)], the infrared high-energy-shift of, ωT, and the variation of relative intensity IE2/E1(TO). These characteristics can be attributed to the existence of the interface effects and the vacancy of N in the GaN nanophase material. This material has a high thermal stability even at 900 °C as indicated through infrared and Raman spectral investigation of annealed samples of as-synthesized nanophase material.

In this work we report a high-tensile ductility in a fully dense bulk nanocrystalline (nc) pure copper sample prepared by electrodeposition. A tensile ductility with an elongation to fracture of 30% was obtained in the nc Cu specimen with an average grain size of 27 nm, which is comparable to that for the coarse-grained polycrystalline Cu. An enhanced yield stress (119 MPa) and a depressed strain hardening exponent (0.22) were observed in the nc Cu sample with respect to the conventional polycrystalline Cu. The high-tensile ductility was attributed to the minimized artifacts in the nc sample, and the grain-boundary sliding deformation mechanism resulted from the numerous amount small-angle grain boundaries and the low microstrain (dislocation density).

A novel optical multilayer filter characterized by symmetrically stepwise graded refractive index profiles and high optical performance was designed. This 33-layer TiO2–SiO2 filter was fabricated by helicon plasma sputtering. The prepared filter exhibited a sharp cutoff reflection band around the central wavelength of 1340 nm and wide pass regions with high transmittance. These results correspond well with calculated estimations. Symmetrically stepwise graded refractive index profiles were demonstrated to effectively contribute to suppression of the sidelobes and to be potentially applicable in the design of other filters.

We have demonstrated that an efficient energy transfer takes place from Yb3+ to Cr4+ in calcium aluminate glasses. Yb3+ improves excitation efficiency at around 980 nm, enhancing emission intensity of Cr4+ fluorescence at 1.2–1.6 μm. Nonradiative energy transfer via electric dipole–dipole interaction between ytterbium and chromium ions was found to be dominant over radiative Yb3+ → Cr4+ energy transfer. A diffusionlimited energy transfer mechanism well explains the decay behavior of Yb3+/Cr4+- codoped glasses. This codoping scheme may be applicable to other Cr4+-containing crystals and glasses.

Photobleaching of the optical absorption band in the 5-eV region of sol-gel-derived germanium oxide glass thin films was examined with the irradiation of the 5-eV light. The photobleaching represented by the saturated absorption coefficient change (−Δα) and the ratio of the neutral oxygen monovacancies to neutral oxygen divacancies concentrations for the germanium oxide were 175 cm−1 and 0.113, respectively. These values are larger than those of the pure germanium oxide bulk glass as well as germanosilicate thin films. The changes in bonding configuration around Ge atom by ultraviolet illumination were analyzed using x-ray photoelectron spectroscopy.

A detailed compositional analysis of high-critical-current-density (Jc) (55 and 65 kA/cm2 at 77 K) (Bi,Pb)2Sr2Ca2Cu3Oy (Bi-2223) tapes was undertaken by energy dispersive spectroscopy in the transmission electron microscope. Structural features were coupled with characteristic compositions of the Bi-2223 phase. The average of all compositional measurements of the Bi-2223 phase was determined to be Bi1.88Pb0.23Sr1.96Ca1.95Cu2.98Oy. However, spatial variations in the Bi-2223 composition and differing phase equilibria were found throughout the filament structure. In particular, a considerable range of Bi-2223 compositions can be found within a single tape, and the lead content of the Bi-2223 phase is significantly depressed in the vicinity of lead-rich phases. The depletion of lead in the Bi-2223 phase around the 3221 phases may be a current-limiting microstructure in these tapes.

The subsolidus equilibria and the primary phase field (crystallization field) of the 110 K high-Tc (Bi,Pb)-2223 ([Bi,Pb]:Sr:Ca:Cu) phase have been determined in the presence of Ag under a 92.5% Ar/7.5% O2 atmosphere (volume fraction). A total of 29 six-phase volumes that include both the (Bi,Pb)-2223 and Ag phases was observed. These subsolidus volumes are similar to those observed without the presence of Ag. The compositional range of initial melts of these volumes (mole fraction basis) covers BiO1.5 from 5.6% to 25.3%, PbO from 0.4% to 13.8%, SrO from 8.4% to 31.9%, CaO from 12.2% to 33.3%, CuO from 21.7% to 40.9%, and AgO0.5 from 1.2% to 6.3%. Based on these data, the primary crystallization field for the (Bi,Pb)-2223 phase in the presence of Ag was constructed using the convex hull technique. A section through this “volume” was portrayed by holding the AgO0.5, SrO, and CaO components at the median value of the 29 compositions while allowing projection on the other three axes (BiO1.5, PbO, and CuO). The net effect of Ag on the melt composition is a reduction in the PbO concentration and an increase in the SrO content. Applications of the liquidus data are also discussed.

A solid metal-bearing precursor route has been used to fabricate Ag-sheathed Bi2Sr2Ca1Cu2O8±x (2212) superconducting tapes. Intimately mixed Bi2O3–Sr–Ca–Cu-bearing powder was first synthesized by a two-stage, high-energy/low-energy mechanical alloying process. The powder was then packed into silver tubes and formed into tapes by drawing and biaxial (Turk's-head) rolling. The precursor tapes were oxidized and converted into Ag-sheathed 2212 by heat treatment at 350–860 °C in oxygen. Subsequent annealing at 897 °C, followed by slow cooling and subsolidus annealing at 850 °C, yielded 2212 grains with enhanced c-axis alignment. The resulting tapes exhibited average and maximum transport Jc (4.2 K, self-field) values of 3.2 × 104 and 6.8 × 104 A/cm2, respectively.

Chemical vapor deposition (CVD) of thin films onto a moving surface is an important material processing technique for semiconductor fabrication, optical coatings, and many other applications. Continuous CVD processing offers an attractive solution to meet high volume requirements. In this study, the deposition on a finite thickness moving susceptor, considering surface reactions, is numerically investigated. When a susceptor is in motion, the reaction zone residence time and the coupling of conduction heat transfer in the susceptor with convection heat transfer in the gas flow significantly alter the deposition rate and film quality. A model is developed to quantify continuous CVD film production for several important design parameters. The numerical model is validated for the deposition of silicon through comparisons with analytical results and experimental data available in the literature. Films produced by continuous CVD are shown to be strongly dependent on susceptor speed, material selection, and susceptor thickness. Susceptor speed is directly linked to residence time in the reaction region, with lower residence times resulting in less time for reaction and heating, hence reducing growth rates. Increased thickness and susceptor thermal diffusivity alters the thermal energy distribution, thereby reducing the susceptor surface temperature and lowering the deposition rate. These effects may be overcome by increasing the length of the heating zone. Film quality is also influenced by the susceptor temperature, since reaction-controlled deposition typically produces different film structure than deposition under diffusion-controlled conditions. Overall, the results obtained demonstrate the feasibility of employing a moving finite thickness susceptor for CVD processing. A correlation of several operational parameters is also obtained for the film thickness. This may be used for the design and optimization of continuous CVD systems. The numerical model may also be used for considering deposition of other materials.

The martensitic transformation behavior of FeMnGe alloy (0–6 wt% Ge) was investigated by resistivity and dilation methods. Ge depresses the martensitic transformation of FeMn alloy. The effect of Ge on starting temperature of martensitic transformation (Ms) temperature of FeMn alloy is −12 K/wt% Ge. Comparing Ge (4s24p2) with Si (3s23p2) and Al (3S23P1), which have similar outer shells of electrons, we found that their effects on the Ms of FeMn alloy are completely different. The result suggests that the outer shell of electron is not the main factor governing the Ms temperature of FeMn alloy, although it is essential in the alloy's antiferromagnetic transition.

Nanosized amorphous alloy powders of Fe25Ni13Co62, Fe38Ni23Co39, Fe40,Ni24,Co36, and Fe69Ni9Co22 were prepared by sonochemical decomposition of solutions of volatile organic precursors, Fe(CO)5, Ni(CO)4, and Co(NO)(CO)3 in decalin, under an argon pressure of 100 to 150 kPa at 273 K. The amorphous nature of these particles was confirmed by various techniques, such as scanning electron microscopy, transmission electron microscopy, electron microdiffraction, and x-ray diffractograms. Magnetic measurements indicated that the as-prepared amorphous Fe–Ni–Co alloy particles were superparamagnetic. The observed magnetization measured up to a field of 1.5 kG of the annealed Fe–Ni–Co samples (75–87 emu g−1) was significantly lower than that for the reported multidomain bulk particles (175 emu g−1), reflecting the ultrafine nature of our sample.

The isothermal reduction of synthetic CoTiO3 and NiTiO3 in hydrogen (1 atm) was investigated using thermogravimetric analysis technique in the temperature range, 928–1287 K (CoTiO3) and 884–1387 K (NiTiO3). Shallow beds of fine titanate powders were reduced by hydrogen at a high flow rate. Quenched samples were analyzed by scanning electron microscopy. The rates of the reaction of the titanates with H2 were very fast during the reduction of Co2+, Ni2+, or Fe2+ ions into metals. The reduction of the remaining titanium oxide was very slow. The activation energy for the reduction of CoTiO3 by hydrogen to Co and TiO2 was evaluated to be 151 ± 1 kJ/mol, and the activation energy for the reduction of NiTiO3 by hydrogen to Ni and TiO2 was evaluated to be 153 ± 1 kJ/mol. The study was complemented by hydrogen reduction of synthetic TiO2 (rutile). The results were also compared with the hydrogen reduction of FeTiO3.

Ordered nanostructure of single-crystalline GaN nanowires in a honeycomb structure of anodic alumina was synthesized through a gas reaction of Ga2O vapor with a constant ammonia atmosphere at 1273 K in the presence of nano-sized metallic indium catalysis. Atomic force microscopy, x-ray diffraction, Raman backscattering spectroscopy, scanning electron microscopy, and transmission electron microscopy indicate that the ordered nanostructure consists of single-crystalline hexagonal wurtzite GaN nanowires in the uniform pores of anodic alumina about 20 nm in diameter and 40–50 μm in length. The growth mechanism of the ordered nanostructure is discussed. The photoluminescence spectrum of this nanostructure is also reported.

A shear-induced ordered structure in an exfoliated polystyrene (PS)/clay nanocomposite is reported. X-ray diffraction (XRD), transmission electron microscopy (TEM), and infrared dichroism techniques have been employed to investigate the shear-induced ordered structure in the exfoliated PS/clay nanocomposite. Compared with the broad amorphous peaks before extrusion, a series of sharp diffraction peaks were observed in XRD pattern for the extruded PS/clay nanocomposite pellet sample, showing that an ordered structure occurred under shear flow. TEM images confirmed directly that the origin of the ordered structure was mainly due to the planar orientation of the primary particles of silicate layers as well as local ordered microstructure of the primary particles, induced by shear flow. The infrared dichroism study indicated that the phenyl group of PS apparently oriented parallel to the film surface, whereas no obvious orientation of the aliphatic chain could be observed. Based on these investigations, a possible mechanism was deduced for the formation of the ordered structure induced by shear flow in the exfoliated PS/clay nanocomposite.

The thermal and mechanical properties of aluminum titanate–mullite composites prepared by a gel-coated powder processing method, namely a mullite precursor gel coating aluminum titanate particles (containing 2.5 wt% MgO), were investigated. A microstructure with both elongated and equiaxed mullite grains was observed in the composite samples. Both the mechanical strength and the thermal expansion coefficient increased with the mullite amount. The mechanical strength showed a strong dependence on the grain size of aluminum titanate with an exponent of −3. Inhibition of aluminum titanate grain growth due to the presence of the mullite phase enhanced the mechanical strength of the composites. The thermal shock resistance tended to decrease as the mullite content increased. The thermal stability of aluminum titanate was improved in the present composite system.

The effects of SiC-nanoparticle and Si3N4-whisker additions on the microstructural evolution and mechanical properties of Si3N4 were investigated. The addition of SiC nanoparticles suppressed Si3N4 grain growth, leading to an improvement in the flexural strength. On the other hand, Si3N4 whiskers in the specimen promoted the formation of large elongated grains, which were found to be beneficial to the fracture toughness of the material. When both SiC nanoparticles and Si3N4 whiskers were added concurrently, large grains were formed in fine matrix grains. The microstructure of Si3N4 was controlled by adjusting the relative concentrations of SiC nanoparticles and the Si3N4 whiskers added. These compositional and microstructural variations of the Si3N4 had significant influence on the mechanical properties, such as strength, fracture toughness, R-curve behavior, and high-temperature strength.

Pure stoichiometric ZrO2 films were deposited on amorphous silica substrates by electron beam evaporation of Zr in the presence of an electron cyclotron resonance oxygen plasma. Grain size, strain, and texture were analyzed by x-ray diffraction and reflection high-energy electron diffraction. Films grown at room temperature are polycrystalline and exist in the cubic phase. Growth at elevated temperatures produces coexisting cubic and monoclinic phases and shows a maximum critical grain size of ??~10 nm for stabilization of the cubic phase. Pole figure analysis indicates a preferred cubic [200] fiber axis for room-temperature growth and dual monoclinic {111} and in-plane textures for films grown at 400 °C. Postdeposition annealing experiments confirm the existence of a critical grain size and suggest mechanisms for grain growth.

We have found that both tetragonal and monoclinic zirconia annealed at temperaturess in the range of 1100 to 1300 °C in atmospheres of low oxygen partial pressures (down to 10−26 Pa) transform slowly to an apparently cubic phase. The transformation can be reversed by increasing the oxygen partial pressure sufficiently, i.e., exposing the sample to air again. These observations were made by 111In/Cd perturbed angular correlation (PAC) measurements of undoped zirconia samples. Upon annealing under various reducing atmospheres PAC spectra show a steadily increasing fraction of Cd probe atoms in a locally cubic environment with the fraction of probe atoms in tetragonal or monoclinic sites decreasing accordingly.

Electrical conductivity and thermopower of Bi2Sr3Co2Ox sintered bodies were first investigated in the temperature range 440–1060 K in air for high-temperature thermoelectric application. The samples fabricated by the sinter-forging method increased their bulk densities and electrical conductivity. The value of thermopower and the temperature dependence of electrical conductivity of the sinter-forged samples were close to that of the single crystal. Evaluating the thermal conductivity of the polycrystalline sample, we calculated a thermoelectric figure of merit Z to be 0.107 × 10−3 K−1 at 1060 K.

Aligned slicon dioxide nanotubes with diameters of 30–40 nm synthesized by the sol-gel template method are presented. This process involves the growth of nanotubes from ordered nanochannel-array pores in anodic alumina. For a silica sol aged at room temperature and dipped for 1 min, nanowires were formed in a shorter period of aging time (2 days); nanotubes connecting with solid nanofibers were obtained in a longer aging time (30 days). The formation of nanotubes depends strongly on the temperature of the sol. For a short dipping time (<1 min), bamboolike nanofibers were prepared when the sol was at high temperature (50 °C); however, perfect nanotubes with the sharp wall were synthetized for the lower sol temperature (5 °C). The lower sol temperature is, the smoother the inside wall of nanotubes is. It is proved that viscosity plays an important role on the morphology of nanotubes.