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We have undertaken a detailed analysis of the X-ray photoelectron spectra obtained from the three polymorphs of [Al.sub.2]Si[O.sub.5]; andalusite, sillimanite, and kyanite. Comparison of the spectra was made based on the chemical bonding and structural differences in the Al- and Si-coordination within each polymorph. The spectra for Si(2p) for all three polymorphs are nearly identical, consistent with the fact that all the Si atoms are in 4-fold (tetrahedral) coordination, whereas the binding energies, peak shapes, and peak widths for Al(2p) vary depending on the type of polymorph. The upper-valence band for all three polymorphs is characterized by four main features derived from O(2p), Al(3s), Al(2p), Si(3s), and Si(3p), and the differences in their contributions are observed. The density of state of the [Al.sub.2]Si[O.sub.5] polymorphs is relatively featureless compared to those observed from [alpha]-Si[O.sub.2] and [alpha]-[Al.sub.2][O.sub.3], suggesting that the orbital overlaps span a greater range in energy. The observed band gap energy for [Al.sub.2]Si[O.sub.5] (sillimanite) was ~9.1 eV, a value in between those for [alpha]-Si[O.sub.2] (~8.6eV) and [alpha] - [Al.sub.2][O.sub.3] (-9.6eV). The conduction band feature of [Al.sub.2]Si[O.sub.5] was experimentally compared to those of [alpha]-Si[O.sub.2] and [alpha]-[Al.sub.2][O.sub.3], and shown that it is indeed intermediate between the [alpha]-Si[O.sub.2] and [alpha]-[Al.sub.2][O.sub.3] phases. Keywords: [Al.sub.2]Si[O.sub.5] polymorphs, X-ray photoelectron spectroscopy, low electron energy loss spectroscopy, valence- and conduction band structures, andalusite, sillimanite, kyanite

Epoxy‐amine thermosetting resins undergo different reactions depending on the amine/epoxy stoichiometric ratio (r). Although many desirable properties can be achieved by varying the stoichiometric ratio, the effects of the variation on the crosslinked structure and mechanical properties and the contribution of these factors to the ductility of materials have not been fully elucidated. This study investigates the brittle‐ductile behavior of epoxies with various stoichiometric ratios and performs curing simulations using molecular dynamics (MD) to evaluate the crosslinked structures. The molecular structure is predominantly branched in low‐stoichiometric ratio samples, whereas the chain extension type structure dominates the high‐stoichiometric ratio samples. As a result, the higher‐stoichiometric ratio samples enhances the ductility of materials and the elongation at break increases form 1.4% (r = 0.6) to 11.4% (r = 1.4). Additionally, the tensile strength (105.4 MPa) and strain energy (7.96 J/cm3) are maximum at r = 0.8 and 1.2, respectively. On the other hand, the Young's modulus is negatively impacted and it decreased from 4.2 to 2.7 GPa with increasing stoichiometric ratio. [ABSTRACT FROM AUTHOR]

Thermopower and electrical conductivity of sodium-doped vanadium pentoxide (V2O5) thin films synthesized by a solution technique were investigated. An aqueous solution based V2O5 thin film is a good candidate for thin film devices using ink-jet deposition and screen printing techniques. To improve its thermoelectric properties for practical applications, Na was systematically introduced into V2O5 as a dopant to study how it influences the thermoelectric properties. A melt-quench technique was implemented to dope various concentrations of sodium ions into sol-gel solutions, and thin films were fabricated from these. X-ray diffraction showed that the Na doped V2O5 samples dominantly form the crystalline phase β-NaxV2O5. It was shown that by increasing the Na concentration, the electrical conductivity could be increased by a factor of up to ∼104, whereas the Seebeck coefficient decreased only by a half. Direct measurement of the thermoelectric power output verified that the power factor was improved up to 350 times. Temperature dependent characteristics of the electrical conductivity and the temperature independence of Seebeck coefficient, respectively, in a range of temperatures examined, suggested that the transport mechanism was a small polaron hopping type. A significant increase in the electrical conductivity was ascribed to the increase in the polaron population and the reduction of the activation energy due to formation of β-NaxV2O5. [ABSTRACT FROM AUTHOR]

Compositional variations of spinel oxides to a reference composition Mn1.68-XCu0.6+X+Y+ZCo0.24-YNi0.48-ZO4 (x and z=0.2, 0.4 and y=+/-0.1) are made. Thermopower and electrical conductivity of these materials are measured in thin film forms obtained through metal organic decomposition. This low-temperature fabrication technique allows the concentration of metastable Mn4+ and Cu1+ ions, which are essential to charge transport in the oxide spinel, to be controlled. All compositions have n-type behavior, and the conduction occurs via polaron hopping between neighboring Mn3+oct and Mn4+oct sites. Compositional variations alter the Mn and Cu oxidation state concentrations, and modify the conductivity and thermopower. Charge balance models are used in some cases to interpret the influences that doping and fluctuating oxygen content have on the variable valence Mn and Cu. After accounting for changes in oxygen concentration, we found that replacing portions of Co with Cu raise both the conductivity and thermopower magnitude, and substituting small amounts of Cu for Ni reduces these thermoelectric factors. Surprisingly, the effects of doping show parallel rises or declines in conductivity and thermopower magnitude. This implies that conductivity is more strongly impacted by the activated carrier mobility than by the number of charge carriers in these oxides. [ABSTRACT FROM AUTHOR]

Perovskite type conducting materials (Ca, Sr)RuO[sub 3] and (Ba, Sr)RuO[sub 3] were prepared by rf magnetron sputtering as bottom electrodes for (Ba, Sr)TiO[sub 3] thin film capacitors. The crystallinity, interface property, and electrical properties of the (Ba, Sr)TiO[sub 3] capacitor applying the perovskite oxide electrodes were investigated. The interface between the dielectric and the electrode were analyzed by high-resolution electron microscopy and Auger electron spectroscopy. The interface had a marked effect on the electrical properties of the (Ba, Sr)TiO[sub 3] thin films. Dielectric constant for the (Ba, Sr)TiO[sub 3] had considerable dependence on the thickness of interfacial layer. The leakage current density of the capacitor was sensitive not only to the structural match but also to the chemical match between (Ba, Sr)TiO[sub 3] and the electrode. © 2000 American Institute of Physics. [ABSTRACT FROM AUTHOR]

The thermopower and electrical conductivity of sodium-doped vanadium pentoxide ([V.sub.2][O.sub.5]) thin films synthesized by a solution technique are examined. The increase in the electrical conductivity is attributed to the increase in the small polaron concentration and a decrease in the activation energy and the increase in power factor has improved the thermoelectric properties of the [V.sub.2][O.sub.5] thin films.

A study made compositional variations of spinel oxides to a reference compositions [Mn.sub.1.68-X][Cu.sub.0.6+X+Y+Z][Co.sub.0.24-Y][Ni.sub.0.48-Z]O4. Thermopower and electrical conductivity of these materials are measured in thin film forms obtained through metal organic decomposition.

Presents information on a study which discussed interfacial reactions between titanium (Ti) and cordierite-based ceramic thin films using x-ray photoelectron spectroscopy. Applicability of bulk thermodynamics in interfacial phenomena; Deposition of Ti at room temperature onto cordierite-based ceramic substrates; annealing of substrates with various levels of Ti coverage.

Perovskite type conducting materials (ca, Sr)RuO3 and (Ba, Sr) RuO3 are prepared by rf magnetron sputtering as bottom electrodes for (Ba, Sr)TiO3 thin film capacitors. The crystallinity, interface property and the effect of interfacial states on the electrical properties of BST are observed.

Single-phase monoclinic aluminum-gallium oxide powders, β−(AlxGa1−x)2O3, have been produced by solution combustion synthesis for Al fraction 0 ≤ x < 0.8. α−(AlxGa1−x)2O3 is observed for x = 1, with mixed α + β for x = 0.8. The contraction in lattice parameters and increase in band gap with increasing Al concentration were characterized by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS), respectively, and are compared with a first-principles density-functional theory calculation. A novel filtering procedure is described to reduce the uncertainty involved in measuring band gap using photoemission, and to remove asymmetry in XPS line shapes caused by differential charging of loose powder. The lattice parameters vary linearly with Al fraction, but exhibit a change in slope at x = 0.5 that is attributed to the difference between aluminum occupying tetrahedral and octahedral sites in the monoclinic lattice. The band gap changes linearly with local stoichiometry, including increasing when aluminum content at the surface is enriched relative to the interior, with a range of over 1.8 eV. [ABSTRACT FROM AUTHOR]