Differences In Interatomic Distances Research Articles

Nanoporous and proton conductive hydrophobic-hydrophilic copolymer thermoset membranes

Copolymers of hydrophobic diglycidyl ether of bisphenol A (DGEBA) vinyl ester (VE) and hydrophilic 2-acrylamido 2-methyl 1-propane sulfonic acid (AMPS) were evaluated as proton conducting membranes for fuel cell applications. Membranes were synthesized using free radical copolymerization in the presence of a common solvent for both monomers, dimethyl formamide (DMF), followed by solvent removal by supercritical CO2 to induce porosity. Micrographs revealed pore sizes below 60 nm with porosity proportional to the initial solvent fraction used. Studies on the states of water showed that the presence of this pore volume significantly altered the freezable water fraction at equivalent AMPS concentrations. Comparison of the moles of water per mole of sulfonic acid (λ) between copolymer membranes and AMPS monomer solutions showed that the nonfreezable water (λ|nonfr) was depressed at high AMPS concentrations, suggesting that differences in interatomic distances between sulfonic acid groups might alter λ|nonfr. The highest average through plane conductivity of membranes was determined to be 30 mS/cm and was comparable to that of Nafion®117 (27 mS/cm). The effective proton mobility, μeff, was calculated and suggested to be a parameter used to capture the effects of membrane structure and swelling while acting as a comparison between different membrane types. Fuel cell tests on membranes at low ion exchange capacities were compared to Nafion®117, with suggestions on improvements of copolymer structures for improved performance. © 2010 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 48: 1245–1255, 2010

Local structure of Y and Ho in calcite and its relevance to Y fractionation from Ho in partitioning between calcite and aqueous solution

Among rare earth elements (REEs), the behavior of Y and Ho in most igneous activities is very close due to the similarity in their ionic radii, while Y fractionates from Ho in marine systems. In this study, in order to elucidate Y–Ho fractionation observed in marine systems in terms of structural chemistry, we examined Ho L III-edge and Y K-edge EXAFS study for two partitioning systems, namely, 1) calcite-aqueous solution (Y–Ho fractionation system) and 2) strong acid cation exchange resin-aqueous solution (non-Y–Ho fractionation system). The results of the EXAFS analysis did not show significant differences in interatomic distances to the most neighboring O atoms between Ho and Y for all the samples. However, it was found that the first shell Ho–O and Y–O distances in the Y–Ho doped calcite were shorter than those in the aqua ion. In contrast, the first shell Ho–O and Y–O distances in the Y–Ho doped resin were similar to those in the aqua ion. Previous studies have suggested that lanthanide (Ln) is more covalent due to 4f orbital participation in bonding relative to Y. Spectroscopic studies on various Ln 3+ complexes show that Racah parameters for 4f electron repulsion in Ln 3+ ions decrease with an increase in covalency of bonding of Ln 3+ ions with anionic ligands. Therefore, our EXAFS results suggest that Y–Ho fractionation in partitioning is possibly attributed to the difference of change in covalency associated with the ligand exchange between Y and Ho, which we have observed as differences in partition coefficients between calcite and aqueous solution.

High-temperature mass spectrometry: Instrumental techniques, ionization cross-sections, pressure measurements, and thermodynamic data (IUPAC Technical Report)

Abstract An assessment of high-temperature mass spectrometry and of sources of inaccuracy is made. Experimental, calculated, and estimated cross-sections for ionization of atoms and inorganic molecules typically present in high-temperature vapors are summarized. Experimental cross-sections determined for some 56 atoms are generally close to theoretically calculated values, especially when excitation–autoionization is taken into account. Absolute or relative cross-sections for formation of parent ions were measured for ca. 100 molecules. These include homonuclear diatomic and polyatomic molecules, oxides, chalcogenides, halides, and hydroxides. Additivity of atomic cross-sections supplemented by empirical corrections provides fair estimates of molecular cross-sections. Causes of uncertainty are differences in interatomic distances and in shapes of potential energy curves (surfaces) of neutral molecules and of molecular ions and tendency toward dissociative ionization in certain types of molecules. Various mass spectrometric procedures are described that render the accuracy of measured thermodynamic properties of materials largely independent of ionization cross-sections. This accuracy is comparable with that of other techniques applicable under the conditions of interest, but often only the mass spectrometric procedure is appropriate at high temperatures.

Phase separation and gap bowing in zinc-blende InGaN, InAlN, BGaN, and BAlN alloy layers

We present first-principles calculations of the thermodynamic and electronic properties of the zinc-blende ternary In x Ga 1− x N, In x Al 1− x N, B x Ga 1− x N, and B x Al 1− x N alloys. They are based on a generalized quasi-chemical approximation and a pseudopotential-plane-wave method. T– x phase diagrams for the alloys are obtained. We show that due to the large difference in interatomic distances between the binary compounds a significant phase miscibility gap for the alloys is found. In particular for the In x Ga 1− x N alloy, we show also experimental results obtained from X-ray and resonant Raman scattering measurements, which indicate the presence of an In-rich phase with x≈0.8. For the boron-containing alloy layers we found a very high value for the critical temperature for miscibility, ∼9000 K , providing an explanation for the difficulties encountered to grow these materials with higher boron content. The influence of a biaxial strain on phase diagrams, energy gaps and gap bowing of these alloys is also discussed.

Texture Control and Electromigration Performance in Al-Based and Cu-Based Layered Interconnects

ABSTRACTTexture control of Al and Cu by underlying refractory metal is discussed. Al texture can be controlled with underlayer metals like as Ti and TiN which have the same atomic arrangement within 3% misfits to Al. Cu texture can be also controlled by underlayer TiN in spite of a large difference in inter-atomic distance of Cu and TiN. Since the epitaxial growth of TiN on Cu is observed, it is suggested that epitaxial growth may occur at the early stage of Cu deposition on TiN.The electromigration performance was evaluated in double level interconnects with W-stud via. It is confirmed that highly <111> textured Al and Cu have high electromigration resistance. Both the diffusion of Cu in Al-Cu and Al drift are suppressed in <111> textured Al-alloy interconnects, and Cu drift is also suppressed in Cu damascene lines formed on <111> textured TiN. Grain boundary diffusion and the interfacial diffusion would be suppressed in highly textured metals with underlayer and it is speculated that interfacial diffusion is more important in Cu damascene lines.

Spin and magnetism of rare-earth intermetallic nickel borocarbides: RENi 2B 2C

The spin and magnetism in quaternary intermetalic borocarbides RENi 2B 2C, REPr, Nd, Sm, Gd, Ho, Tm are determined by first-principles density functional theory, using the embedded cluster formalism. Spin polarization of the lattice by the RE moments is examined in detail, and related to observed magnetic ordering phenomena. The observed superconductivity and regions of coexistence with antiferromagnetism are discussed in terms of the lattice polarization, magnitude of moments, and differences in interatomic distances.

新たな観点から見つめ直した高温超伝導体の結晶構造

The extended electrostatic valence rule is applied to several superconductors and related compounds to explain differences in interatomic distances within coordination polyhedra. A general structural feature is indicated that bonds between apical oxygen and atoms opposite to Cu on CuO2 sheets are relatively short and covalent. A new method in conformity with this idea is proposed for describing the crystal structures of superconductors.

A geometric model of deviations from Vegard's rule

There is much evidence that X-ray measurements of sufficient accuracy reveal deviations from the linear dependence of unit-cell parameters on composition, i.e., departures from Vegard's rule. The dependence of such deviations on composition for a random solid solution with one substitutional position (Ax1 Bx2C is usually of a parabolic form: δa=x1x2σ where σ is positive. Many attempts to explain these observations are based on elastic models. It is known that less than 50% of the predictions of these models are correct. An alternative model under consideration is a simple geometric one. It is concerned with secondary atomic displacements around substitutional defects, i.e., shifts of the second nearest neighbors. The result is structurally dependent and the analysis deals with binary solid solutions of B1 (CN=6), B3 (CN=4), and B2 (CN=8) structure types. For instance, in sodium chloride structure-type solid solutions, the following simple equation is valid, δh=(3/2)x1x2(R)2/R, where R is the difference in interatomic distances of pure components and R is the average interatomic distance. Calculations for NaCl−KCl, NaCl−NaBr, KCl−KBr, and other systems are in good agreement with experimental data.

Vibrational progressions in vibronically induced transitions

It is shown that progressions of totally symmetric vibrations in vibronically induced spectra do not show the same intensity distribution as comparable progressions in allowed spectra. This is due to cross terms, involving both totally symmetric and inducing mode coordinates, in the Herzberg–Teller expansion. These cross terms express the modulation of the vibronic coupling resulting from differences in interatomic distances between the borrowing and lending states. The effect is universal, as opposed to effects based on normal-coordinate rotation or totally symmetric inducing modes, and enters even in the absence of anharmonic coupling. It leads to anomalous intensity distributions which, moreover, are different for emission and absorption spectra. Quantitative estimates are presented which indicate that it should be readily observable in many molecules.

A comprehensive X-ray study of the ferroelectric–ferroelastic and paraelectric–paraelastic phases of Gd2(MoO4)3

The crystal structure of Gdz(MoO4)a has been investigated both at room temperature and at elevated temperatures below and above the ferroelectric-ferroelastic transition temperature (~ 160°C). Space group, unit-cell dimensions, and formula units per unit cell Pba2 (C8v), a= 103881 +00003, b= 104194+0.0004, c= 107007+0.0006/~,, Z = 4 at 25°C and PS421m (D~), a=7.393 +0.002, c= 10.670 + 0.004/~, Z= 2 at 183 °C. Full-matrix least-squares refinements have been carried out with anisotropic thermal parameters with two single-crystal diffractometer data sets measured at 25 and 183 °C, yielding conventional R values of 0.032 (3000 reflections) and 0-028 (880). The high-temperature structure comes close to the average structure of the two ferroelectric-ferroelastic orientations. The differences in interatomic distances between the two modifications are all less than 0.05 .~. Ferroelectric-ferroelastic switching can be accomplished through two macroscopically equivalent switching mechanisms. Changes in interatomic distances of nearest neighbors upon switching are all less than 0.05 ,~,. The main difference between the two ferroelectric-ferroelastic orientations results through movements of several oxygen atoms by as much as 0.7.~. The spontaneous polarization was calculated assuming point charges Gd 3+ and [MOO4]'from positional parameters: Ps = 0.175/tC.cm -2, in good agreement with experiment. Since most of the dipole moments cancel out within the unit cell, Gd2(MoO4)3 can be described as a canted antiferroelectric. The temperature dependence of intensities and peak widths of superstructure reflections has been monitored through the transition temperature. Below the transition temperature, temperature-dependent physical properties can be accounted for by gradual changes in positional parameters towards the high-temperature structure. The mechanism of the phase transition is discussed in terms of the 'positional order-disorder' and the 'soft mode' model. The results obtained in the refinement of the room-temperature structure are compared with results of an independent study of this structure by Keve, Abrahams & Bernstein.

Magnetic Susceptibility of Iron-Nickel Alloys in Liquid and Solid States

The magnetic susceptibilities of various Fe-Ni alloys have been measured through their melting points up to 1600°C. The susceptibilities of the alloys with less than 60 % Ni increase discontinuously on melting, while those of the alloys with more than 60 % Ni decrease. The temperature variation of the susceptibilities is approximately expressed by the Curie-Weiss law in the liquid state as well as in the solid state, but the Curie constants and the paramagnetic Curie temperatures of liquids are in general different from those of solids. These results can be explained by assuming that the atomic magnetic moments remain unaltered and that the magnetic interaction varies with the interatomic distance as indicated by the Bethe-Slater curve. The change of susceptibility at the melting point is solely due to the difference in interatomic distance between the liquid and the solid. It is expected, in some cases, that the especially strong dependence of the magnetic interaction on the interatomic distance results ...