Crystallization and reaction kinetics of a crystallizable K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder with 17–40 vol% titania powder were investigated. The initially amorphous K2O–CaO–SrO–BaO–B2O3–SiO2 glass powder formed cristobalite (SiO2) and pseudowollastonite [(Ca, Ba, Sr)SiO3] during firing. The above crystalline phases were completely replaced by a crystalline phase of titanite [(Ca, Sr, Ba)TiSiO5] when the amount of added titania was greater than a critical value, e.g., 10 vol%, at 99–1100 °C. A chemical reaction taking place at the interface between titania and the glass was attributed to the above observation. The dissolved titania changed the composition of the glass, and the dissolution kinetics was much faster than the formation of cristobalite and pseudowollastonite. Activation energy analysis showed that the crystallization of titanite [(Ca,Sr,Ba)TiSiO5] was controlled by a reaction-limiting kinetics of formation for the Ti–O bond.

Substitution effects of Ta5+ by Nb5+ in BiTa1−xNbxO4(0 ≦ x ≧ 1.0) on photocatalytic, photophysical, and structural properties were investigated. The powder x-ray diffraction and Rietveld structural refinement showed that the structure of BiTa1−xNbxO4 at R = Nb/Bi = 0.0 and 0.5 is a triclinic system with space group P1. However, the structure at R = 0.2, 0.8, and 1.0 is an orthorhombic system with space group Pnna. Ultraviolet-visible diffuse reflectance spectroscopy measurement revealed that the band gap of orthorhombic samples is narrower than that of triclinic compounds. The H2 evolution was obtained from an aqueous CH3OH/H2O solution and pure H2O with BiTa1−xNbxO4 under ultraviolet irradiation. The orthorhombic samples exhibit much higher activity than that of triclinic compounds. The orthorhombic compound at R = 0.2 showed the highest activity, which is higher than that of the well-known TiO2 photocatalyst.

Results of magnetization and magnetic susceptibility measurements on undoped and Co-doped FeSi2.5 single crystals are presented. The temperature dependence of the magnetic susceptibility of the Co-doped sample in the range of 5–300 K can be explained by temperature-dependent contributions due to paramagnetic centers and the carriers excited thermally in the extrinsic conductivity region. The values of the paramagnetic Curie temperature and activation energy of the donor levels were estimated. It is also shown that the magnetic susceptibility of Co-doped samples cooled in zero external field and in a field are different. This resembles the properties of spin-glasses and indicates the presence of coupling between magnetic centers.

We used an Ising model to determine whether boundary mobility is an intrinsic material parameter or if it depends on the nature of the driving force for boundary migration. The simulations included both capillarity and external field-driven boundary migration. The external field-driven, flat boundary simulations showed that boundary mobility depends strongly on boundary inclination at low temperature but not at high temperature. On the other hand, the boundary mobility in capillarity-driven migration shows no dependence on boundary inclination and is independent of the boundary migration geometry. An initially circular grain shrinks as a circle and a half-loop boundary retracts with profiles predicted under the assumption that the boundary mobility is isotropic during capillarity-driven migration even when the temperature is very low and the external-field-driven boundary migration is extremely anisotropic. However, when an external field is superimposed on the capillarity driven migration of the circular boundary, the circular grain exhibits well-defined corners consistent with the simulation lattice symmetry. In this case, the boundary mobility is much different than if the external field were omitted. This is a clear demonstration that the boundary mobility can depend on the nature of the driving force for boundary migration.

This paper reports the influence of lanthanum-doping on the dielectric behavior of Pb(Fe1/2Ta1/2)O3 relaxor ferroelectrics, where the La ions are incorporated into the B-site of the perovskite constructing unit and the resultant charge imbalance is compensated by the presence of free charge carriers (holes). The formulated compositions were fabricated using one-step preparation method, and a nearly pure perovskite phase was attained, as verified by XRD analysis. Both the dielectric permittivity maximum (ε′max) and the temperature at which ε′max occurs (Tm) are progressively reduced by La-doping. The degree of frequency dispersion, however, is promoted, indicating the weakened ferroelectric couplings among the oxygen octahedra as a result of lanthanum incorporation. Moreover, the breadth of paraelectric to ferroelectric phase transition is broadened with an increase in lanthanum content, due to enhanced inhomogeneity and increase in the number of B-site cations. Frequency spectroscopy at a certain temperature below Tm reveals a widening of the size distribution of ferroelectric nanodomains, which is characteristic of relaxor microstructure, by La-doping.

The microstructure of Ag-doped La2/3Sr1/3MnO3 (LSMO) thin films deposited on (001) LaAlO3 single-crystal substrates was systematically investigated in cross section and plan view by high-resolution electron microscopy and analytical electron microscopy. The results showed that the films deposited at 750 °C were perfectly epitaxial with or without Ag-doping. No Ag in the doped film was detected. On the other hand, the LSMO films deposited at 400 °C were less perfect. With increasing Ag-doping level, the shape of LSMO grains became irregular, and the grain size increased gradually. Large polycrystalline clusters consisting of LSMO, AgO, and Ag grains formed in the doped films, and the amount and size of them increased with increasing Ag-doping level. Ag existed at the LSMO grain boundaries in its elemental state. A growth process for the LSMO-Ag system is discussed based on the experimental results. The enhancement of the magnetic spin disorders at the grain boundaries and interfaces caused by doping Ag could result in an improvement of low-field magnetoresistance.

Electrospun nanofibers have applications in the areas of filtration, composites, biomaterials, and electronics. Controlling the surface properties of these nanofibers is important for many applications. Nanofibers can also be used as unique substrates for observing the growth of deposited films and creating nanoscale structures. In this work, electrospun poly(meta-phenylene isophthalamide) (MPD-I) nanofibers were used as substrates for creating nanoscale structures out of carbon-based materials and metals. MPD-I was used because it can be electrospun into nanofibers with diameters smaller than 10 nm and it has good thermal stability. MPD-I nanofibers were coated with carbon, copper, and aluminum using plasma enhanced chemical vapor deposition and physical vapor deposition methods. Some of the aluminum-coated nanofibers were then converted into nanotubes. Transmission electron microscopy was used to determine the thickness, uniformity, and grain size of the coatings on the fibers and the nanotubes.

The grain growth kinetics and ordering behavior of direct-current magnetron sputter-deposited Ni75at.%Al25at.% alloy films were investigated using in situ isothermal annealing in a transmission electron microscope. Both normal and abnormal grain growth modes were observed. The normal grain growth kinetics under isothermal heating from 300 to 700 °C were found to comply with the Burke law d = K/dn−1, where d is grain size and K and n are constants with respect to time. The grain boundary mobility parameter K was found to obey an Arrehnius rate law with an apparent activation energy of 1.6 eV, and n was found to increase gradually from 5.2 at 300 °C to 8.7 at 700 °C. Abnormal grain growth occurred at 500 °C or higher, and grain coalescence was identified as an important operative mechanism. It was also observed that the initially as-deposited state of the films was crystalline with a disordered face-centered-cubic structure, but ordering into the equilibrium L12 intermetallic structure followed from annealing at temperatures above approximately 500 °C.

Hexagonal 6H– and 4H–SiC wafers were implanted with (1−1.5) × 1016 cm−2 germanium ions at room temperature and at 700 °C with subsequent annealing between 1000 and 1600 °C. Structural changes in the SiC matrix were studied in detail by means of transmission electron microscopy (TEM). After implantation at room temperature the hexagonal SiC matrix becomes amorphous and, after annealing, recrystallizes into cubic SiC. The latter process was accompanied by the creation of voids and cracks. In case of high-temperature (700 °C) implantation, where amorphization was avoided, no polytype change in as-implanted and annealed SiC wafers was observed. In annealed samples nanocrystalline precipitates with high Ge content were observed in high-resolution TEM images.

Nano-sized copper particles are loaded into the pores of monolithic mesoporous silica by soaking and drying, followed by thermal reduction of copper nitrate [Cu(NO3)2]in a hydrogen atmosphere at 973 K for 90 min. It has been shown that copper nanoparticles are isolated from each other and highly uniformly dispersed inside the pores of silica. It is found that the surface plasmon resonance peak of the copper particles shows a significant red-shift with decreasing the particle size, which is in contrast to the corresponding fully embedded system. The peak decreases with exposure time to air and exhibits a linear relation with logarithmic exposure time. This red-shift phenomenon and decrease are explained on the basis of the structural features of this new composite or coexistence of local porosity and the nanoparticle's free surface in contact with air.

SrBi2Ta2O9 (SBT) thin films were prepared by the radio-frequency (rf ) magnetron sputtering method on Pt/Ti/SiO2/Si substrates. The composition and orientation of SBT thin films were changed by the control of sputtering parameters such as pressure and rf power. As the sputtering pressure increased from 2.5 to 300 mtorr, the film was changed from Sr- and Bi-deficient SBT film to stoichiometric film. The SBT thin films with stoichiometric composition showed good electrical properties. As the rf power increased from 25 to 40 W, the Sr content decreased. However, the Bi content was maximized in the power of 30 W, where the (200)-predominant SBT thin films were fabricated. In lower power of 25 W, typical polycrystalline SBT films were obtained. The Sr and Bi contents in both films were not deficient. However, at the higher power of 35 and 40 W, the secondary phase appeared due to the Sr deficiency. The Bi content of (200)-predominant SBT film was higher than that of polycrystalline films. The degree of the (200) orientation depended on the magnitude of excess Bi content. It is also suggested that the (200)-predominant SBT films were formed by the decomposition of SBT phase to the Bi and Sr atoms caused by rf power control and the lower atomic migration energy along the a axis.

Fiber textured Sr0.53Ba0.47Nb2O6 ceramics were reactively sintered to ≥95% of the theoretical density from a mixture of SrNb2O6 and BaNb2O6 powders. Texture in 〈001〉 was obtained by templated grain growth on 〈001〉-oriented acicular KSr2Nb5O15 template particles. The most highly textured ceramics had a peak dielectric constant of 23,600 (at Tc = 128 °C), a remanent polarization (Pr) of 20.3 µC/cm2, a saturation polarization (Psat) of 24 µC/cm2 (69–96% of single crystal), and a piezoelectric charge coefficient (d33) of 84 pC/N (76–93% of single crystal). A model, correlating polarization with grain orientation, predicts that Pr increases sharply when a percolating grain network forms to transfer charge between elongated grains.

A solution of a polymeric precursor for silicon carbide (SiC) was subjected to electrostatic atomization in the cone-jet mode to spray droplets on a zirconia substrate. The resulting deposit was heated to 1300 °C to obtain SiC relics. Precursor and ceramic relics were characterized by microscopy. The size distribution of the droplet relics was studied at several flow rates of the solution to the electrostatic atomization chamber. The results show that by controlling the flow rate SiC relics approximately 5 μm in diameter can be produced.

Planar thin films of dye-doped silica were prepared by sol-gel synthesis. The optical properties of the films were characterized by transmittance measurements in the visible-infrared range and by photoluminescence. Micropatterns whose feature size was on the order of 2.4 μm, were imprinted on the film surface by a simple soft lithography approach. An optical microscope interfaced to a charge-coupled device camera was used to image the imprinted patterns and to analyze the patterned films photoluminescence. A sensitive spectral narrowing of the emission, which occurred only in micropatterned films, was attributed to the lateral confinement of the luminescence due to the micrometer-scale modulation of refractive index produced by the embossing procedure.

The continuous hydrothermal synthesis of nanoparticles of two metal oxides (α–Fe2O3 and Co3O4) is described. Two variations of the technique were investigated, involving the precipitation reaction between a metal salt solution and a hydroxide solution at ambient conditions and at elevated temperatures. Elevated temperatures resulted in more uniform particles of α–Fe2O3 and Co3O4, although the actual sizes of the particles were apparently unaffected by the temperature. This behavior was attributed to the species present in solution and the solubilities of the cation(s), both of which were calculated via a thermodynamic model for the systems under study.

To improve the strength of brazed joints, a TiN-coated layer was introduced as an interlayer and reaction barrier for ceramic-ceramic joints. Al2O3, Si3N4, and ZrO2 ceramics were brazed with a Ag–Cu–In–Ti alloy after a TiN coating was applied on the ceramic substrates. The strength of as-brazed and thermally treated Al2O3 specimens with a TiN coating was found to be equivalent to that of bulk Al2O3. However, the Si3N4 and ZrO2 systems showed a significant reduction in joint strength. The difference in the strength can be explained on the basis of the bond strength of the coating, the reaction products, and residual stress developed at the joint interfaces.

The crystallization kinetics of Sr0.7Bi2.3Ta2O9 (SBT) and 0.7SrBi2Ta2O9–0.3Bi3TiTaO9 (SBT-BTT) thin films formed by the sol-gel and spin coating techniques were studied. Phase formation and crystal growth are greatly affected by the film composition and crystallization temperature. Isothermal kinetic analysis was performed on the x-ray diffraction results of the thin films heated in the range of 730 to 760 °C at 10 °C intervals. Activation energy and Avrami exponent values were determined for the fluorite-to-Aurivillus phase transformation. A reduction of approximately 51 kJ/mol in activation energy was observed for the SBT-BTT thin films, and an Avrami exponent value of approximately 1.0 was obtained for both the SBT and SBT-BTT. A comparison is made, and the possible crystallization mechanism is discussed.

The growth of polycrystalline silicon on glass by low-pressure chemical vapor deposition and in situ laser induced recrystallization was investigated with the aim to study the influence of the seed layer and the mechanism of the recrystallization dynamics on the structural and morphological properties of the grown film. A seed layer was used to trigger the solidification process of many additional in situ laser-crystallized overlayers. One-dimensional calculations of the thermal flow produced by laser irradiation were used to clarify the complex interaction between the substrate and the molten silicon surface layer during nucleation and growth. The experiments show the relevant role played by the seed layer and the peculiar shaping of the film surface due to the preferential aggregation of molten silicon. Compact polysilicon films with thicknesses up to 4 μm with almost monocrystalline grains of 1–2-μm size were obtained.

In the Ni–Mo system, two possible nonequilibrium states located near Ni3Mo were predicted through calculation of the total energies of eight possible structures of the A3B type as a function of their lattice constant(s) by applying the Vienna ab initio simulation package. Comparatively, Gibbs free energy diagrams were constructed from Miedema's model and, in general, the calculated results were in accordance with the prediction from ab initio calculation. Besides, the prediction of one of the nonequilibrium states was in agreement with the fact that a metastable hexagonal-close-packed Ni3Mo phase was indeed observed in Ni75Mo25 multilayer films upon thermal annealing, and calculated lattice constants matched well with those determined by diffraction analysis in experiments as well.

Nanowires were produced by injection of molten Hg and Pb into chrysotile nanotubes. The breakdown of chrysotile and the surface tension of the molten metals are the limiting factors for the filling procedure. The thermal stability of chrysotile nanotubes was investigated by infrared spectrometry, thermogravimetry, differential thermal analysis, and x-ray diffraction analyses. For short-term thermal annealing (30 min) the tube morphology remains stable up to 700 °C. The high surface tension of both molten Pb and Hg (γLV > 200 mN/m) requires external pressure for the melts to penetrate into the tubes. Filling of the tubes was achieved under high pressure and high temperature conditions compatible with the stability range for chrysotile determined in the annealing experiments. Transmission electron microscopy observations confirmed high filling yields for both metals. Almost all nanotubes were partially filled with lead. The length of continuous wires ranged from tens to hundreds of nanometers. Additional experiments with tin were not successful.