Non-linear dielectric effect in the acetone-benzene and acetophenone-benzene systems

The non-linear dielectric effect has been studied for acetone and acetophenone, and their solutions in benzene. With the NDE results obtained in this work and the dielectric polarization calculated from literature values of the permittivity, density and refractive index, the mean values of the square and the fourth power of the dipole moment were calculated. Assuming dipolar association of the acetone and acetophenone molecules to be restricted to dimerization, the Gibbs free energy ΔG^o of the dimerization process is determined.     

Magnetic and dielectric properties of YbFe2−xMnxO4 (0?x?1)

We have investigated the magnetic and dielectric properties of YbFe_2−xMn_xO₄ (0?x?1), which is an Fe-site-substituted system of new multiferroic oxides RFe₂O₄ (R=Y, Ho-Lu). X-ray diffraction measurements show that a solid solution is formed between YbFe₂O₄ (x=0) and YbFeMnO₄ (x=1) for 0?x?1, whereas only compounds with x=1 (i.e., RM₁M₂O₄; M₁ and M₂=trivalent and divalent cations, respectively) have been known for the Fe-site substitution in RFe₂O₄. The valence of the Mn ion is determined to be ∼2+, consistently with the suppression of low-temperature magnetization by the Mn substitution. The magnetic transition temperature (T_N) and the dielectric constant (ε′) decrease monotonically with increasing x. This result plausibly confirms that the magnetic and dielectric properties in oxides isostructural with RFe₂O₄ are governed by the electron transfer between Fe-site ions, unlike ordinary ferroelectrics and dielectrics, in which the ionic displacement plays a key role. The possibility for application is briefly discussed as well.     

Synthesis and electrical properties of variable-composition phases Rb1 − x A1 − x R1 + x (MoO4)3 (0 ≤ x ≤ 0.2; A = Mg, Mn, Co, Ni; R = Sc, Yb, Lu)

Subsolidus region of the ternary systems Rb₂MoO₄-AMoO₄-R₂(MoO₄)₃, in which variable-composition phases Rb_{1 ? x} A_{1 ? x} R_{1 + x} (MoO₄)₃ crystallizing in the monoclinic system (space group C2) are formed, was studied. Their crystallographic parameters were calculated; temperature dependences of the electrical conductivity, dielectric constant, and dielectric loss tangent were analized.     

Heteromolecular structures in aqueous solutions of dimethylformamide and tetrahydrofuran,according to molecular dynamics data

The complex dielectric permittivity of aqueous solutions of tetrahydrofuran and dimethylformamide in wide ranges of temperature (220–300 K) and pressure (0.1–12 MPa) is studied by means of molecular dynamics. The autocorrelation functions of the dipole moments of molecules are calculated. Dielectric permittivity spectra are obtained. The dielectric relaxation times are determined as functions of the tetrahydrofuran and dimethylformamide concentrations in the indicated binary mixtures. The dielectric relaxation frequency shifts toward low frequencies in the range of tetrahydrofuran and dimethylformamide concentrations x ≤ 0.5 molar fraction, due to the formation of heteromolecular structures with hydrogen bonds. This is confirmed by the negative values of the excess dielectric permittivities of binary solutions at x ～ 0.3–0.4 molar fraction.     

Sign ambiguity in dipole moment derivatives of Br2CO

Signs of the dipole moment derivatives, ?p_x/?S₄ and ?p_x/?S₅ where p_x is the dipole moment vector along an axis perpendicular to the CO bond in the plane of the molecule and S_j are the symmetry coordinates for the B₁ vibrations of Br₂CO have been re-evaluated from the reported ?p/?Q_i values (p being the dipole moment of the molecule and Q_i the normal coordinates) and the L matrix elements. The new set of dipole moment derivatives fits well with similar parameters for Cl₂CO and F₂CO.     

Subsolidus phase relations and crystal structures of R-Ca-Cu-O (R=Nd, Sm, Gd, Tm) systems

The subsolidus phase relations of R₂O₃-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950° in air. There exists a ternary compound Ca_14−xR_xCu₂₄O₄₁ (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca_2+xR_2−xCu₅O₁₀ (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca_14−xR_xCu₂₄O₄₁ possesses a layered orthorhombic structure and is isostructural to Sr_14−xCa_xCu₂₄O₄₁. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca_2+xR_2−xCu₅O₁₀ solid solution is isostructural to Ca_2+xY_2−xCu₅O₁₀, the structure of which is based on an orthorhombic “NaCuO₂-type” subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels.     

Dielectric relaxation losses in lead chloride and lead bromide: Localized dipoles

A further analysis of previous reported measurements of dielectric relaxation losses in lead chloride and lead bromide crystals shows that the dipoles may occupy several energetically different positions, giving rise to localization of the dipoles and anomalous behaviour of the susceptibility. This energy difference is determined. Inspection of the crystal structure shows that the anion vacancy, being the mobile part of the dipole (which is an associate like (Me_Pb·V_X)^x or (O_X·V_X)^x where X = Cl, Br), may jump indeed between halide ion sites with different coordination number.A comparison between the dipole concentration as calculated from the observed losses and the associate concentration as estimated from ionic conductivity experiments leads to the conclusion that local field corrections in the calculations are important.     

About the concentration dependence of the anisotropy in the magnetic susceptibility of some aromatic compounds in the liquid phase,studied by NMR

Magnetic field induced quadrupolar line splittings in the ²H NMR spectra of pyridine and metadinitrobenzene are reported. From the splittings the anisotropy in the magnetic susceptibility Δ_x has been deduced. The concentration dependence of the quadrupolar magnetic field effect, and hence of Δ_x, of nitrobenzene, metadinitrobenzene and naphthalene has been investigated. The effect of different solvents has also been studied. Environmental effects of Δ_x have been found to be substantial in several cases. The relation of the present experiments with the Cotton-Mouton effect is discussed in detail.     

Significantly Improved Colossal Dielectric Properties and Maxwell—Wagner Relaxation of TiO2—Rich Na1/2Y1/2Cu3Ti4+xO12 Ceramics

In this work, the colossal dielectric properties and Maxwell—Wagner relaxation of TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ (x = 0–0.2) ceramics prepared by a solid-state reaction method are investigated. A single phase of Na_1/2Y_1/2Cu₃Ti₄O₁₂ is achieved without the detection of any impurity phase. The highly dense microstructure is obtained, and the mean grain size is significantly reduced by a factor of 10 by increasing Ti molar ratio, resulting in an increased grain boundary density and hence grain boundary resistance (R_gb). The colossal permittivities of ε′ ~ 0.7–1.4 × 10⁴ with slightly dependent on frequency in the frequency range of 10²–10⁶ Hz are obtained in the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics, while the dielectric loss tangent is reduced to tanδ ~ 0.016–0.020 at 1 kHz due to the increased R_gb. The semiconducting grain resistance (R_g) of the Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics increases with increasing x, corresponding to the decrease in Cu⁺/Cu²⁺ ratio. The nonlinear electrical properties of the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics can also be improved. The colossal dielectric and nonlinear electrical properties of the TiO₂–rich Na_1/2Y_1/2Cu₃Ti_4+xO₁₂ ceramics are explained by the Maxwell–Wagner relaxation model based on the formation of the Schottky barrier at the grain boundary.     

Active Pd/Fe(OH)x catalyst preparation for nitrobenzene hydrogenation by tracing aqueous phase chlorine concentrations in the washing step of catalyst precursors

By tracing the chlorine concentrations in the aqueous solutions containing the catalyst precursors, Pd/Fe(OH)_x catalysts with different activities can be controllably prepared. For the hydrogenation of nitrobenzene, the active Pd/Fe(OH)_x catalysts were obtained from aqueous solutions with chlorine concentrations below 18 ppm and above 8 ppm.     

The crystal structure of α-copper vanadate

The crystal structure of α-copper vanadate has been determined and refined by full-matrix least-squares procedures using automatic diffractometer data to a residual R = 0.050 (R_w = 0.059). The space group is rhombohedral, $\text{R}\text{3}$, with hexagonal unit cell a = 12.857(3) and c = 7.161(2) Å (a_R = 7.797(2) Å and α = 111.06(1)°). On the basis of the detailed structural analysis the contents Cu_7?xV₆O_19?x with x = 0.22 are proposed for the rhombohedral cell. Copper is in the divalent and vanadium in the quadrivalent state. The structure is based on a cubic close-packed array of oxygen ions with the vanadium ion occupying an octahedral site, one copper in a partially occupied octahedral site and the other copper in a tetrahedral site. The latter is one of the few examples of tetrahedrally coordinated copper.     

Photopolymerization of methyl methacrylate using triethylamine-nitrobenzene complex as photoinitiator

Photopolymerization of methyl methacrylate in bulk and in solution at 40° using triethylamine nitrobenzene (TEA-NB) complex as photoinitiator was studied kinetically. Initiator order x, given by the relation R_pα([TEA][NB])^x, was 0.28 for [TEA][NB] < 25 × 10 ^?8 mol² · l^?2; for higher values of [TEA][NB], x was practically zero. Monomer order was 1.1 in benzene and pyridine but much less than unity (0.65–0.70) in carbon tetrachloride and chloroform. Kinetic analysis indicated that the initiation process was monomer and solvent dependent. The halomethane solvents enhanced the polymerization rate through their active participation in the initiation or radical-generation steps. End-group analysis indicated incorporation of basic (amino) end-groups in the polymers. The kinetic non-ideality was explained on the basis of significant initiator-dependent termination through primary radicals or via degradative transfer to initiator.     

Effect of phase purity on dielectric properties of CaCu3+xTi4O12 ceramics

Different amounts of CuO are used to synthesize CaCu_3+xTi₄O₁₂ (CC_xTO, −1 ≤ x ≤ 1) powders in this work. In order to investigate the effects of Cu constituent on the componential, morphological, and dielectric properties, 975 °C is selected as the sintering temperature to prepare the ceramic pellets with different x values from −0.2 to 0.2. They basically keep the same component and morphology despite the different Cu constituents in the ceramics. Cu component has complex effects on their dielectric properties, whose changes are not linear with the Cu increase. However, the CC_0.2TO ceramic sample has the most frequency-independent dielectric constant and the lowest dielectric loss.     

The linear correlation of the (ΔR′m)i function determined for the ortho derivatives of phenol,aniline, benzaldehyde,and nitrobenzene

The additivity of selected chromatographic data with a group of ortho derivatives of phenol, aniline, benzaldehyde, and nitrobenzene has been proved with the help of the theoretical approach developed by Snyder (1–5), and this concept is assumed to be useful in the attempt to predict the R_f, values of substances with known structures or in elucidating such structures with compounds having known R_f, values.     

Overlap population and the homopolar dipole

The expression {[^S_AB/(1 + S_AB)]R/2} 2e is shown to be an upper limit approximation to the homopolar dipole. It results from adding the overlap population 4C₁C₂S_AB to the atom with the smaller orbital radius. Dipole moments calculated from this partitioning are closer to the experimental values than those computed with equally sophisticated techniques from the standard gross atomic populations. Atomic charges are identical to Löwdin's in the limiting case when S_ABR/2 = $\text{x}$_AB, but the calculations are over non-orthogonalized AO's.     

Superionic transport in solid fluoride solutions with a fluorite structure

Results of systematic research into ionic transport in solid solutions M_{1 ? x} R_xF_{2 + x} and Na_{0.5 ? x} R_{0.5 + x} F_{2 + 2x} (M = Ca, Sr, Ba, Cd, Pb; R = rare-earth elements) with the fluorite structure are reviewed. The mechanism of anionic conduction is analyzed. The link between ionic transport and defects in the structure of these crystals is discussed. Potentialities of their application in electrochemical devices are considered.     

Pyrochlore solid solutions (LaxY1−x)2Mo2O7, x = 0.0 to 0.5. Spin-glass-like behavior

The (La_xY_1−x)₂Mo₂O₇ system was investigated in the range x = 0.0 to x = 0.5. Single-phase materials exist up to x = 0.4; the x = 0.5 composition has a small impurity contamination. The lattice constants are linear with x and range from 10.224 Å (x = 0.0) to 10.461 Å (x = 0.5). These lattice constants span the same range as the R₂Mo₂O₇ series from R = Y to R = Nd. In this series, there is a discontinuous change from ferromagnetic long-range order to short-range spin-glass-like order between R = Gd and R = Tb. Yet, the solid solutions all show spin-glass-like properties with maxima in the susceptibility in the 20–25 K range and sample-history-dependent effects at lower temperatures. Deviations from the Curie-Weiss Law occur well above the susceptibility maxima. The Weiss constants change from −61 to +41 K for x = 0.0 and x = 0.5, respectively, indicating a competition between antiferromagnetic and ferromagnetic exchange interactions. This competition, coupled with the inherent frustration of the Mo⁴⁺ lattice in space group Fd3m is a possible origin of the spin-glass properties.     

Structural and electrical properties of (1−x)(Na1/2Bi1/2)TiO3-xPb(Mg1/3Nb2/3)O3 solid solution

Structural, dielectric and piezoelectric properties of (1−x)(Na_1/2Bi_1/2)TiO₃-xPb(Mg_1/3Nb_2/3)O₃ (NBT-xPMN) solid solution have been investigated. An addition of PMN into NBT transformed the structure of sintered samples from rhombohedral to pseudocubic phase where x is larger than 0.1. In calcined powders, however, the intermediate structure were observed between rhombohedral and cubic phases near x=0.1. The formation of solid solution between NBT and PMN modified the dielectric and piezoelectric properties of NBT to be suitable for high temperature dielectric and piezoelectric material. With increasing the content of PMN, the temperature-stability of ε_r(T) increased and the high temperature dielectric loss decreased. In addition, the piezoelectric property of NBT-xPMN was enhanced, for the decrease of coercive field and conductivity promoted the domain reversal under the high electric field of the poling process.     

X-ray and neutron powder diffraction studies of Ba(NdxY2−x)CuO5

Ba(R,R′)₂CuO₅ (R,R′=lanthanides and Y) plays an important role as a flux-pinning agent in enhancing the superconducting properties of the Ba₂(R,R′)Cu₃O_6+x (R,R′=lanthanides and Y) coated conductors. Using X-ray diffraction and neutron diffraction, we found that the Ba(Nd_xY_2−x)CuO₅ solid solution adopts two structure types. In the Nd-rich region (1.8?x?2.0), the materials are of brown color (commonly referred to as the ‘brown phase’), and the structure is tetragonal with space group I4/mbm (no. 127). In the Y-rich region (0.0?x?1.4), the materials are green (commonly referred to as the ‘green phase’) and the structure is orthorhombic with space group Pnma (no. 62). A two-phase region (1.4<x<1.8) exists between the orthorhombic and tetragonal phases. The crystal chemistry and crystallography of the orthorhombic ‘green phase’ series, Ba(Nd_xY_2−x)CuO₅ (isostructural to BaY₂CuO₅), are discussed in this paper.     

Preparation and applications of novel fluoroalkyl end-capped acrylamide oligomers/polythiophene nanocomposites

Thiophene monomer reacted with ferric chloride in the presence of a variety of fluoroalkyl end-capped N-(1,1-dimethyl-3-oxobutyl)acrylamide oligomers [R_F-(DOBAA)_x-R_F] to afford nanometer size-controlled R_F-(DOBAA)_x-R_F oligomers-polythiophene composites [R_F-(DOBAA)_x-R_F/PTh]. R_F-(DOBAA)_x-R_F/PTh nanocomposites thus obtained were demonstrated to have a good dispersibility and stability in methanol to give a transparent brown solution. In addition, these fluorinated nanocomposites were applied to the surface modification of common organic polymers such as poly(methyl methacrylate), and were dispersed regularly above the polymer surface.