Nanoparticles of Ag, Au, Pd, and Cu have been prepared by the reduction of their salts by ethyl alcohol under refluxing conditions in the presence of polyvinylpyrrolidone (PVP). In the case of Au and Cu, it was necessary to use magnesium metal as a catalyst during the reduction. The nanoparticles are in the 5–35 nm range in the case of Ag, Au, and Pd, but there is considerable agglomeration in the case of Cu even in the presence of PVP.

A method for the preparation of pure amorphous Fe2O3 powder with particle size of 25 nm is reported in this article. Pure amorphous Fe2O3 can be simply synthesized by the sonication of neat Fe(CO)5 or its solution in decalin under an air atmosphere. The Fe2O3 nanoparticles are converted to crystalline Fe3O4 nanoparticles when heated to 420 °C under vacuum or when heated to the same temperature under a nitrogen atmosphere. The crystalline Fe3O4 nanoparticles were characterized by x-ray diffraction and M¨ossbauer spectroscopy. The Fe2O3 amorphous nanoparticles were examined by Transmission Electron Micrography (TEM), Differential Scanning Calorimetry (DSC), Thermogravimetric Analysis (TGA), and Quantum Design SQUID magnetization measurements. The magnetization of pure amorphous Fe2O3 at room temperature is very low (<1.5 emu/g) and it crystallizes at 268 °C.

CaSi2 and CaSi have been investigated by Auger Valence Electron Spectroscopy (AVES). Some drastic differences of the Auger peak due to 3s states in the Si atoms were observed in the Si[2s, 2p, V] Auger spectra. The peak that arised from valence electron states in the Ca atoms was observed in the Ca[2p, 3p, V] Auger spectra for both Ca-silicides. This result suggests that the Ca–Si bonds are partially ionic. However, the number of the valence electrons in Ca atoms for CaSi was larger than that for CaSi2. This result implies that the part of homopolar bonds between the Si and Ca atoms in CaSi is stronger than that in CaSi2. Based on these results, it has been concluded that the change of the Si [2s, 2p,V] Auger spectra is associated with the difference of the part of homopolar bonds between the Si and Ca atoms.

A BN film containing comparable amounts of sp2 and sp3 phases was subjected to a gas-phase chemical etch in a hot-filament environment containing 1% CH4 in H2. After a partial etch, examination by FTIR shows that the sp2 was preferentially etched, leaving a larger sp3 fraction than in the unetched film. The possibility that preferential etching could be used to increase the purity of cBN films is discussed.

Vanadium dioxide thin films (VO2) have been deposited by laser ablation. The temperature dependence of resistivity and temperature coefficient of resistance (TCR) for each deposition condition were investigated. It was clarified that the TCR at room temperature (RT) can be optimized by controlling the oxygen pressure introduced during deposition as the deposition parameter. In the result, larger TCR's at RT were observed for the oxygen deficient condition of VO2 than for oxygen-richer samples. Obtained TCR values were 0.072/K and 0.045/K at 25°C for VO2 thin films deposited onto R-cut sapphire and SiO2/Si, respectively.

Geometrical effects on the cooling performance of the thin film thermoelectric (TFTE) modules were investigated by varying the film thickness and the number of p/n couples of the (Bi, Sb)2Te3/Bi2(Te, Se)3-based system which were fabricated by the flash evaporation technique. Maximum temperature difference (δTmax, maximum cooling) and optimum input current (Iopt) increased with film thickness for a fixed number of couples. For the case of given thickness, however, Iopt decreased with the number of couples, maintaining almost constant δTmax. The measured values for the cooling characteristics were compared with the results obtained through computer simulation work by the finite difference method (FDM). The thinner the film and the larger the number of p/n couples of the modules, the larger was the deviation between the experimental and the simulated values.

Alumina aerogels were synthesized by low temperature CO2 supercritical drying (SCD) of gels via the Yoldas process. The aerogels have a surface area of ˜425 m2/gr, similar to that obtained under high pressure/temperature SCD. The surface area and the cluster size of the aerogels are strongly influenced by the amount of acid during gelation. Gels and aerogels were studied by small angle x-rays scattering (SAXS), and the data were analyzed using the Fisher–Burford equation. The SAXS results along with TEM observations support the existence of a hierarchical aggregation at the gelation stage, having a mass fractal dimension of Dm = 2.6−2.8. During the SCD the morphology collapses to form a structure with surface fractal dimension Ds = 2.6−2.9.

We present the first high temperature x-ray diffraction (HTXRD) studies of in situ quasicrystal-crystal and crystal-crystal transformations in Ti–Zr–Ni alloys. Together with differential scanning calorimetry studies, these x-ray measurements indicate three separate paths for the Ti–Zr–Ni quasicrystal-crystal transformation: single exothermic, single endothermic, or multiple endothermic. The mode of transformation depends on the alloy composition and the level of environmental oxygen. The crystalline products include the Ti2Ni, MgZn2 Laves, α−(Ti, Zr), and β−(Ti, Zr) phases. In the absence of oxygen, the endothermic transformation of the quasicrystal demonstrates that it is the lowest free energy (stable) phase at the Ti53Zr27Ni20 composition. Oxygen stabilizes the Ti2Ni phase, eliminating both the quasicrystal and the MgZn2 Laves phase, at partial pressures as low as a few hundred ppm.

Titania matrices prepared by a sol-gel technique were doped with several cations (La, Zn, Al, K, Na, Ca, Ba, and Co). The effect of the dopants on the thermal and structural properties of the materials is analyzed. The dopant concentration was 2% mol with respect to titanium, and in all cases the same anion (nitrate) was used. The transition temperatures from amorphous to anatase and from anatase to rutile were measured using x-ray diffraction. The amorphous-anatase transition is independent, for almost all samples, of the type of dopant used; however, the anatase-to-rutile phase transition depends strongly on the kind of cation. This means that the temperature range where the anatase phase exists can be controlled by choosing the appropriate dopant. We have found a correlation between the anatase-rutile phase transition temperature and the radius of the cations and their electric charge.

Lead zirconate titanate (PZT 40/60) thin films were fabricated on electroded silicon wafers using chemical solution deposition. Two different chelating agents, acetic acid and acetylacetone, were used in the synthesis of the precursor solutions. The microstructure of the acetylacetone-derived film was characterized by nucleation at the platinum electrode and a columnar growth morphology (˜100−200 nm lateral grain size). In contrast, the acetic acid-derived film was characterized by both columnar grains nucleated at the electrode, and larger (˜1 μm) grains nucleated at the surface of the film. Using Fourier transform infrared (FTIR) diffuse reflectance spectroscopy, we also noted that the pyrolysis behavior of the films was dependent on the chelating agent employed. The acetylacetone-derived films, which displayed only one nucleation event, were also characterized by a higher pyrolysis temperature than the acetic acid-derived films. Previously, microstructural differences of this nature were attributed to variations in “precursor structure.” In this paper, we discuss an alternative mechanism for the observed microstructural variations in films prepared from different solution precursors. In the model proposed, we discuss how changes in film pyrolysis temperature result in a change in film crystallization temperature, and hence, a change in the effective driving force for crystallization. We show how the change in crystallization driving force is expected to impact the thin film microstructure due to the accompanying variations that occur in the barrier heights for interface (lower electrode) and surface nucleation. A standard approach to nucleation in glasses is used as the basis of the proposed model. Finally, we also discuss how the model can be used to understand the observed effects of heating rate and thickness on the microstructure of solution-derived thin films.

180° domain boundaries in flux-grown lead titanate single crystals show intriguing domain boundary extreme fringe contrast using transmission electron microscopy. Symmetrically distributed domain boundaries with alternate contrast have been observed, indicating that opposite displacement vectors exist one by one at boundaries. If appropriate reflection vectors were employed, an inclined domain boundary shows reversed fringe contrast. An analysis based upon the two-beam dynamical theory and a rule similar to stacking-fault contrast analysis was employed to predict the geometric configuration of a 180° domain boundary using the extreme fringe contrast (EFC) behavior. Appropriately choosing reflection vectors and utilizing the EFC reversal, a displacement vector as well as the polarization vector arrangement across a 180° domain boundary can be unambiguously identified. Employing the information derived from diffraction patterns and a tilting experiment across a nearby 90° boundary, the whole polarization configuration can be uniquely determined.

This paper presents a method for determining diffusivities in solids where the diffusing species desorbs or reacts at the external surfaces, and where the diffusivity does not vary appreciably with concentration. The method involves measuring the flux of the diffusive species out of the solid under the influence of a temperature program. A general model is developed, based on nonisothermal Fickian diffusion, which is applicable to solid particles with slab or spherical geometry. The solution is presented both as an analytical expression and as correlation charts of experimentally observable quantities. These charts are contour diagrams of the temperatures of peak diffusion rate with ln(E/R) and ln(D0/h2) as the axes, where E and D0 are the activation energy and pre-exponential terms of the diffusivity expression D = D0 exp(−E/RT), where R is the gas constant, and h the size of the particles. This paper deals exclusively with the case of oxygen diffusion in the vanadium oxide system. In this case, vanadium oxide was reduced in a reactive ammonia stream at conditions in which the surface reaction was fast compared to the diffusive transport process. Using this method the diffusion parameters were found to be D0 = 1.9 × 10−5 cm2 s−1 and E = 101 kJ/mol. The method was checked by varying the crystallite size of the vanadium oxide sample in the range 2h = 0.14−0.29 μm.

This paper presents a new form of linear free energy (LFE) relationship for diffusive mass transport in oxides and other binary compounds. The relationship applies to a family of related compounds. For a given substance, i, solid-state diffusivity is related to the equilibrium constant Ki or the free energy of transformation, , via a transfer coefficient γ, through the expression ln Di = γ ln Ki + constant . The system investigated here is the series of suboxide intermediates of vanadium pentoxide formed during temperature-programmed synthesis of vanadium nitride. The value of γ for this series is 0.27. The diffusivity values are determined by fitting a mathematical model to the experimental data. Diffusivity data are presented graphically in contour diagrams which correlate pre-exponential values, activation energies, particle sizes, and heating rates used in the temperature-programmed syntheses. An Evans–Polanyi linear relation, , relating activation energy, Ei, to enthalpy change of transformation, , via a transfer coefficient α = 0.53, is also shown to exist for the above system. The discrepancy between α and γ is resolved by using the Horiuti concept of the stoichiometric number of the rate-determining step.

The deformation behavior of fine-grained, α-phase rich silicon nitride materials has been studied between 1823 and 1923 K, both in compression and in tension. It is first shown that the higher the α-phase content, the better the superplastic forming ability. A large tension-compression flow asymmetry was evidenced. For instance, shear-thickening flow shows up in compression whereas shear-thinning is observed in tension. Furthermore, much higher flow stresses and hardening rates are reported in compression than in tension. Elongations of more than 80% were achieved for strain rates between 2.5 and 5 × 10−5 s−1. In the light of our results and of the abundant literature dealing with the high temperature deformation in silicon nitride, a sketch of the different deformation stages is proposed, which emphasizes the tension-compression asymmetry. Starting from the promising results obtained at the laboratory scale, the feasibility for net-shaping of a real part was demonstrated by hot-forging of a parabolic shell.

Yttria-stabilized cubic zirconia powders and coatings produced by the sol-gel method have been investigated by Perturbed Angular Correlation Spectroscopy (PAC). Results indicate that the metastable cubic phase is retained during heating and cooling cycles. The hyperfine interaction that describes this cubic phase, once crystallized, exhibits two components in a constant ratio of 4 : 1. The components represent different vacancy configurations. For the fast movement of oxygen vacancies starting at 750 °C, which is reflected by the damping of the hyperfine pattern, an activation energy of 0.96 eV was determined.

This paper deals with the mechanisms and kinetics of interactions between screen printed and fired PbO layers and ceramic substrates: alumina and beryllia. The interaction with alumina occurs via two main processes: (i) a reaction between PbO and Al2O3 grains, which induces the formation of a crystalline phase, Pb2Al2O5; and (ii) an interdiffusion process involving Pb and the intergranular amorphous phase in the ceramic substrate. This latter process results in a compositional change of the intergranular phase at considerable depths inside the ceramic substrate, as well as in the formation of a high lead glass layer on the substrate surface. Since PbO is not completely reacted, the Pb penetration in the ceramic is diffusion limited (penetration depth , where td is the reaction time) with an activation energy of 1.20 ± 0.05 eV. The ceramic microstructure significantly affects the interaction processes.

Modified lead titanate of 0.9PbTiO3 −0.1Pb(Mg0.5 W0.5)O3 thin films have been deposited onto Pt-coated Si substrates by pulsed laser deposition. Films were crystallized in situ during deposition or by post-depositional heat treatment (post-annealing). Compositional and structural characterization showed that the phase formation and microstructure of the films were highly sensitive to deposition conditions. Perovskite single phase films were formed in situ at 650 °C, PO2 = 40 Pa as well as by post-annealing amorphous films at 650 °C. In the post-annealing process, the amorphous as-deposited phase was crystallized to perovskite and/or pyrochlore, and the ratio of perovskite to pyrochlore was found to be influenced by the depositional PO2. Depending on the deposition temperature, the grain structures of the crystallized films were columnar or equiaxed. A relatively homogeneous surface morphology was obtained by deposition at a lower pressure (PO2 = 13 Pa). The in situ crystallized films showed variable crystallographic orientation. The more (111) oriented films had the lowest remanent polarizations and the highest coercive fields. A method for preparing randomly oriented films, via a two-step deposition process with intermediate annealing, is believed to give the most consistent results and the best ferroelectric properties at the present level of development.

Ordering and microwave dielectric properties of Ba(Ni1/3Nb2/3)O3 have been investigated using x-ray diffraction, transmission electron microscopy, energy-dispersive spectroscopy, and a network analyzer. Samples sintered at 1400 °C for 2 h were disordered and showed the presence of Nb-rich liquid phase at grain boundary junctions. Degree of ordering increased with following annealing at 1300 °C. Growth of the ordered region during the annealing process was discussed in terms of nucleation and growth. A long-range order parameter was calculated using structure factor. Measurements of microwave dielectric properties showed that permittivity and temperature coefficient of resonant frequency decreased with ordering, and quality factor increased with ordering. The correlation between microwave dielectric properties and ordering was discussed in terms of covalency of bonding, inhomogeneous charge distribution, and defects concentration.

The results of measurements of dielectric constants, in the vicinity of ambient temperature, are presented for eight barium titanium niobium oxides (BaTi1+2nNb4O13+4n for n = 0, 1, 2, 3, 4; Ba3Ti4Nb4O21, Ba3Ti5Nb6O28, and Ba6Ti2Nb8O30) in polycrystalline ceramic form. The dielectric constants are in the range of 30 to 70. The results of dielectric measurements on solid solutions obtained by partial substitution of Ta for Nb are also reported. These substitutions do not dramatically increase the dielectric constants. One material, Ta-substituted Ba3Ti5Nb6O28, has a very low temperature coefficient of dielectric constant at K ≈ 45.

Rhombohedral Pb(Zr0.70Ti0.30)O3 thin films of four different well-defined textures, namely, (100), (111), bimodal (110)/(111), and (100)/(111), were prepared by a sol-gel method. The films were characterized in terms of grain size, presence of second phases, surface roughness, columnarity of grains, and other microstructural features. The dielectric, ferroelectric, and fatigue properties were investigated, with emphasis on the hysteresis switching characteristics. Results are discussed from the reference point of the allowable spontaneous polarization directions available for the different textures. The values of coercive field, remanent and saturation polarization, and slope of the loop at the coercive field, at saturating fields can be qualitatively explained based on the texture, independent of microstructural differences. The occurrence of surface pyrochlore, however, is observed to affect the functionality of the saturation curves, particularly for the samples of bimodal texture. Shearing of the hysteresis curves of the bimodal films is also attributed to surface microstructural features. The occurrence of nonswitching 71° or 109° domains in the (111) and (110)/(111) textured films is hypothesized based on a comparison with the data from the (100) textured film. Corrected saturation polarization values agree with the spontaneous polarization values of rhombohedral PZT single crystals and published calculated values for rhombohedral PZT ceramics. The fatigue characteristics show increases in the switching component of polarization in the range 103−107 bipolar cycles, particularly for the (111) textured sample. Onset of fatigue is observed for all samples between 107 and 108 switching cycles.