Samples of Co clusters embedded in a carbon fiber matrix have been prepared using a heat-treatment method of cellulose fibers with ion-absorbed cobalt cations. Depending on the heat-treatment temperature used, different cluster sizes have been obtained, ranging from superparamagnetic clusters (average size 10 nm) to ferromagnetic nanoparticles (size between 30 and 200 nm). The formation of graphite planes surrounding the nanoparticles has been observed.

Partially reacted mixtures of Pb(ZrxTi1−x)O3 and its corresponding starting oxide components were obtained by a high-energy ball milling process. The partially reacted powders were characterized by x-ray diffraction and scanning electron microscopy techniques. The sintering behavior of the milled mixtures has demonstrated a distinct volumetric expansion before the densification of the samples, which clearly shows the occurrence of a reactive sintering process of the partially reacted powders. Such process requires a lower densification temperature as compared with the PZT powders produced by the conventional solid-state reaction process. PZT ceramics were found to form directly from the partially reacted powders sintered at 900–1200 °C. The dielectric and ferroelectric properties of the PZT ceramics as a function of sintering temperature and milling time were also studied and discussed.

Amorphous silicon–nitrogen (a–Si1−xNx:H) alloys, thin films, and multilayers deposited by ultrahigh-vacuum plasma-enhanced chemical vapor deposition were studied and modeled by x-ray reflectivity (XRR) measurements. The analysis of XRR data obtained from the single-layer samples allowed us to calculate the density, thickness, and interface roughness of each layer. To check the deposition parameters, the deviation (tnom – texp)/(tnom) of the measured thickness texp from the nominal thickness tnom was evaluated. Based on these results, a simulation of a multilayer film, obtained by deposition alternating stoichiometric and substoichimetric layers was carried out. It is shown that the best fitting is obtained by introducing into the XRR calculation a thickness distribution with a standard deviation related to the deviation (tnom – texp)/(tnom) estimated for the single layers.

By introduction of the chemical effects of fluorine, thick cubic boron nitride (cBN) films with high phase purity and low residual stress were synthesized on silicon substrates by dc-bias-assisted dc jet chemical vapor deposition in an Ar–N2–BF3–H2 system. In this paper, the characterization of the films by scanning electron microscopy, glancing-angle x-ray diffraction, infrared spectroscopy, and Raman spectroscopy was done. Among these techniques, Raman spectroscopy was intensively studied, and a method was established to evaluate the crystallinity and residual stress of the cBN films from the line width and peak shift of Raman charactersitic peaks. The influences of the experimental parameters, i.e., bias voltage, substrate temperature, and deposition time, on the film quality were systematically studied. An experimental window for the deposition of cBN films was described. The cBN films deposited under optimized conditions showed the similar line width of both Raman TO and LO modes and thus a crystallinity comparable to that of 4–8-μm cBN single crystals synthesized by high-ressure and high-temperature methods.

The structure and dielectric properties of Bi2O3–ZnO–Nb2O5-based ceramics with pyrochlore–fluorite biphase structure were investigated. Mixed-sintered ceramics were prepared by two precalcined constituents in the system of x[Bi1.5Zn0.5(Zn0.5Nb1.5)O7]−(1 − x)Bi3/4Nb1/4O7/4 (0.05 ≤ x ≤ 0.35), where Bi1.5Zn0.5(Zn0.5Nb1.5)O7 is a cubic pyrochlore (α) and Bi3/4Nb1/4O7/4 is a defect cubic fluorite (F). The phase composition of the mixed-sintered ceramics were characterized as a biphasic structure with a distorted pyrochlore (β) and a fluorite (F) coexisting. The phase ratio of β pyrochlore and F fluorite is related to the chemical composition x. The dielectric properties of the ceramics gradually change with their structure.

Typical titanium-based perovskite oxides Eu1−xBaxTiO3 (x = 0.6−0.8), Eu1−xKxTiO3 (x = 0.2,0.32), and La0.7 (Na,K)0.3TiO3 were synthesized by high pressure and temperature using RE2O3 (RE = La,Eu), TiO2, alkaline, or alkaline earth carbonates as the starting materials. X-ray diffraction data analysis showed that there was a structural transformation in Eu1−xBaxTiO3 by varying Ba content [i.e., from cubic (x = 0.6,0.7) to tetragonal (x = 0.8)], and that samples Eu1−xKxTiO3 and La0.7(Na,K)0.3TiO3 crystallized in the cubic perovskite structure. 151Eu Mössbauer spectroscopy and electron paramagnetic resonance measurements revealed mixed valence of Eu2+/Eu3+ in samples Eu1−xBaxTiO3 and Eu1−xKxTiO3, while Ti ions were present in pure Ti4+ state. Cubic Eu1−xKxTiO3 was metastable, which decomposed into a mixture of perovskite and pyrochlore phases at high temperatures as accompanied by an oxidation process from Eu2+ to Eu3+. For samples La0.7 (Na,K)0.3TiO3, Ti3+ signals were clearly observed. The reduction mechanisms for Eu ions at A site and Ti ions at B site in the perovskite oxides are discussed in terms of the chemical nature of the framework ions and substitution ions under high pressure and temperature.

Some of the most interesting compounds from both technological and a scientific viewpoint can be found within the B–C–N composition triangle. Despite all the attention that some phases on the vertices and sides of the triangle have attracted, few works have focused inside the triangle itself. A laser-assisted chemical vapor deposition system was used to deposit B–C–N phases over fused quartz substrates. Two sets of gaseous precursors were used, namely B2H6 + NH3 + C2H4 and B2H6 + (CH3)2NH. The coatings were characterized regarding chemical composition, structure, and morphology. Hardness measurements were also carried out with a depth-sensing indentation instrument. It was found that depending on the gas phase, different regions of the BCN solid composition triangle are accessed. Coatings ranging from pure h-BN to pure B4C were obtained, as well as mixtures of these with BxCyNz compounds.

A series of photochromic sol-gel films are prepared through entrapping tungsten heteropolyoxometallates (PW12O403−, SiW12O404−) and molybdenum heteropolyoxometallate (PMo12O403−) into a kind of inorganic–organic matrix cohydrolyzed from tetraethylorthosilicate and 3-aminopropyltriethoxysilane. The films show reversible photochromicity. Irradiated with ultraviolet light, the transparent films change from colorless to blue. Then, bleaching occurs when the films are in contact with air or O2 in the dark. The Keggin-type polyanions interact with R–NH3+ cations strongly, and thus disperse uniformly in the sol-gel matrix, as proved by Fourier transform infrared spectra and x-ray diffraction. The molybdenum heteropolyoxometallate sol-gel film has higher photochromic efficiency and much slower bleaching than its counterparts of tungsten heteropolyoxometallate. A charge-transfer model which is supported by electron spin resonance and related literature [T. Yamase, Chem. Rev. 98, 307, (1998)] is put forth to explain the above experimental results.

Silica–polyimide nanocomposites were prepared by hot-pressing mixtures of polyimide and highly porous silica powder. The silica powder was produced using a sol-gel process that generates pores as small as 15 Å. The effects of loading, cure, and post-cure temperature on fracture toughness were investigated. The addition of silica particles improved the fracture toughness from 0.5 to a maximum of 1.9 MPa m0.5. However, fracture toughness dropped at silica weight percentages ≥30%. The cure and post-curing temperatures have a strong influence on toughness; post-curing exposure ≥400 °C reduced toughness. Transmission electron microscopy examination of the fracture surfaces indicated that the toughness improvements may occur at the nanometer scale due to crack pinning and branching induced by the nanoporous silica particles.

Crystallization behavior of amorphous Zr65Cu17.5−xAl7.5Ni10Agx (x = 0, 5) alloys prepared by melt spinning and injection casting techniques has been studied using differential scanning calorimetry, x-ray diffractometry, and transmission electron microscopy. Ag addition changes crystallization sequence of the amorphous phase. The amorphous Zr65Cu17.5Al7.5Ni10 alloy crystallizes via simultaneous precipitation of icosahedral phase and NiZr2 phase in the first crystallization step whereas that in Zr65Cu12.5Al7.5Ni10Ag5 alloy crystallizes via precipitation of only icosahedral the phase. Partial replacement of Cu by Ag in Zr65Cu17.5Al7.5Ni10 alloy stabilized the icosahedral phase relative to competing intermetallic phases resulting in suppression of the precipitation of the NiZr2 phase, enhancement of the precipitation of icosahedral phase, and reduction of undercooled liquid range. Crystallization behavior of the amorphous Zr65Cu12.5Al7.5Ni10Ag5 alloy is not affected by cooling rate during solidification. Johnson–Mehl–Avrami analysis of isothermal transformation data suggests that the formation of the quasicrystalline phase is not entirely polymorphic in nature and may involve partitioning of the solute at later state.

We report on needlelike silicon nitride nanowires grown on silicon using ammonia microwave plasma heating. Scanning electron microscope reveals that the nanoneedles are either straight, slightly bent, or kinked with sharp tips. Transmission electron microscope shows that the sizes of the nanowire tips are less than 5 nm and the structures are well crystallized. X-ray diffraction on the surface of the as-deposited structures indicates that both α-silicon nitride and β-silicon nitride exist. Catalyst particle splitting and merging explain observed structure derivation and bending. A vapor–liquid–solid model is employed to explain nucleation and growth mechanism.

Nanocrystalline nickel films of about 0.1 μm thickness grown by sputtering with and without substrate bias possessed average grain sizes of 9–25 nm. Variation in substrate bias at room and liquid nitrogen temperature of deposition strongly affected grain structure and size distribution. Qualitative studies of film surfaces showed variation in roughness and porosity level with substrate bias and film thickness (maximum of 8 μm). The films had tensile residual stress, which varied with deposition conditions. The hardness values were much higher than those of coarse-grained nickel but decreased with an increase in the film thickness because of grain growth.

We report on the relaxation of ultraviolet-radiation-induced structure and long-lasting phosphorescence in Eu2+-doped glass samples with compositions of xAl2O3 · 40SrO · (60 − x)SiO2· 0.05Eu2O2 · 0.05Dy2O3 (x = 0, 10, 30) (mol%). After irradiation by an ultraviolet lamp (λmax = 254nm) with a power density of 5 mW/cm2 for 30 min, a visible light (peaking at 510 nm) could be seen with the unaided eye in the dark even 24 h after the removal of the activating light. Thermostimulated luminescence glow curves, x-ray absorption, and electron-spin-resonance spectra were measured. We suggest that the long-lasting phosphorescence in the Eu2+-doped glass samples resulted from the recombination of electrons and holes at shallow traps in the glass matrix that can be thermally released at room temperature, and energy transfer between the recombination centers and Eu2+ ions.

Morphological evolution of cobalt germanide epilayers, CoxGey, was investigated in situ by scanning tunneling microscopy and spectroscopy and reflection high-energy electron diffraction, as a function of deposition method and, hence, the phase content of the epilayer. During reactive deposition epitaxy, in which Co atoms were evaporated onto a flat pseudomorphic Ge/Si(001) wetting layer at 773 K, the first phase formed was cobalt digermanide, CoGe2, in the form of elongated pyramidal islands. Each of these three-dimensional islands has locally exerted an additional strain on the Ge wetting layer already strained at the Ge/Si(001) interface, lifting the layer metastability and causing, in turn, the formation of three-dimensional Ge pyramids underneath every CoGe2 island. Solid-phase epitaxy of Co onto the same Ge/Si(001) epilayer resulted in the formation of more Co-rich germanide islands. Coupling of strain from these germanides to the epitaxial Ge/Si(001) strain has also facilitated a two-dimensional-to-three-dimensional transition of the Ge layer, however, with the germanide islands located at the Ge pyramid troughs, rather than crests. The difference in the relative location of germanide and germanium islands in these two cases is explained by accommodation of the large lattice-constant germanides at the more relaxed regions of the Ge pyramid crests and the smaller lattice-constant at the compressed Ge pyramid troughs.

Alkali halides such as KBr, KI, CsBr, and CsI were added to Dy3+-doped Ge–Ga–S glasses, and their effects on the 1.31-μm emission property were investigated. The intensities of the 1.31-μm emission (6F11/2 · 6H9/2 → 6H15/2) increased at the expense of the 1.75-μm emission intensity (6H11/2 → 6H15/2) with the alkali halide addition. The lifetimes of the 1.31-μm emission level also increased as much as 35 times from 38 μs for Ge–Ga–S glass to 1320 μs for the glass containing 10 mol% CsBr. These enhancements occurred only when the ratio of MX (M = K, Cs; X = Br, I)/Ga was equal to or larger than unity. Raman spectra of Ge–Ga–S–CsBr glasses indicated the formation of [GaS3/2Br]− complexes, which provide the preferred sites for Dy3+. Due to this new local environment of Dy3+, the multiphonon relaxation rates from the Dy3+:6F11/2 · 6H9/2 level decreased by approximately four orders of magnitude. The enhancement in the 1.31-μm emission properties with alkali halide addition supports the potentials of these glasses as hosts for the Dy3+-doped fiber-optic amplifiers.

Conducting polyaniline/barium titanate (PANI/BaTiO3) composites exhibiting piezoresistivity properties have been synthesized by the in situ deposition technique by placing a fine grade powder of BaTiO3 in the polymerization reaction mixture. The polyaniline was formed preferentially on the ceramic particles giving a much higher yield for PANI than in absence of the BaTiO3 These composites exhibited piezoresistivity with the piezosensitivity being maximum at a certain composition. The current–voltage characteristics clearly revealed a nonlinear space charge controlled charge transport process. A large hysteresis in these characteristics was also observed which was dependent on the BaTiO3 content in a composite. The various results have been explained on the basis of the charge transport mechanism in the heterogeneous conducting material having insulating domains dispersed in it.

The tensile creep behavior of yttrium- and lanthanum-doped alumina (at dopant levels below the solubility limit) was examined. Both compositions (100 ppm yttrium, 100 ppm lanthanum) exhibited a uniform microstructure consisting of fine, equiaxed grains. The creep resistance of both doped aluminas was enhanced, compared with undoped alumina, by about two orders of magnitude, which was almost the same degree of improvement as for materials with higher dopant levels (in excess of the solubility limit). In addition, measured creep rupture curves exhibited predominantly steady-state creep behavior. Our results, therefore, verified that the creep improvement in these rare-earth doped aluminas was primarily a solid-solution effect.

Highly densed silicon nitride ceramics with various α/β phase ratios were produced by pulse electric current sintering process. The β-phase content of Si3N4 in sintered materials varied from 20 to 100 wt% depending on the sintering condition. The microstructure was observed by scanning electron microscopy and investigated by image analysis. Young's modulus, hardness, fracture toughness, and strength were strongly dependent on the α/β phase ratio. The fracture toughness increased from 4.6 MPa m1/2 for 20-wt% b-phase content to 8.2 MPa m1/2 for 95-wt% β-phase content, and the fracture strength showed a maximum value of about 1.6 GPa at 60-to-80-wt% β-phase content.

Low-density, open-cell nickel base superalloy foams have been synthesized by a high-rate, electron beam-directed vapor deposition process and their mechanical properties evaluated. The deposition process uses an open-cell polymer foam template upon which is deposited a metal alloy coating. The electron beam evaporated flux was entrained in a rarefied transonic gas jet and propagated along the flow stream lines through the polymer structure. After vapor deposition, the polymer template was removed by low-temperature thermal decomposition. The resultant ultralightweight metal foams consisted of a three-dimensional open cell, reticulated structure possessing hollow triangular ligaments with relative densities of <3%. Their mechanical integrity was increased by either pressureless or transient liquid phase sintering. The mechanical properties of these ultralightweight metal foams were comparable to theoretical predictions for open-cell, reticulated foams.

BaTiO3-coating films were prepared from a solution containing poly(vinylpyrrolidone) (PVP) of molar composition Ba(CH3COO)2:Ti(OC2H5)4:PVP:CH3COOH:H2O: C2H5OH = 1:1:0.5:27:4:5, via nonrepetitive, single-step dip-coating. The gel films were found to be converted into BaTiO3 films via evaporation of the solvent and CH3COOH below 210 °C, decomposition of PVP at 210–360 °C, decomposition of CH3COO− below 440 °C, and crystallization at 500–610 °C. The decomposition of PVP was accompanied by the progress of the condensation reaction, which resulted in significant reduction in film thickness. When the gel films were heated isothermally at 700 °C, crack-free BaTiO3 films as thick as 0.9 μm were obtained. When the gel films were heated isothermally at 360 °C and then at 700 °C, the film became denser. Higher dielectric constants around 290 were found for the film that underwent the isothermal heat treatment at 360 °C. A slower rate of PVP decomposition was thought to be the key for the film densification.