Large spontaneous polarization and clear hysteresis loop of a room-temperature hybrid ferroelectric based on mixed-halide [BiI3Cl2] polar chains and methylviologen dication

The search for hybrid organic-inorganic materials, which have the great advantage that they can be synthesized at moderate temperature (T < 200 °C), remains a great challenge in the field of ferroelectrics. Here, a room-temperature ferroelectric material with interesting characteristics, (MV)[BiI(3)Cl(2)] (MV(2+) = methylviologen), is reported. Its structure is based on polar inorganic chains resulting from a remarkable Cl/I segregation induced by methylviologen entities, which coincide with the fourfold polar axis of the tetragonal structure. Of great importance is that this room-temperature hybrid ferroelectric displays a clear electrical hysteresis loop with a large spontaneous polarization (>15 μC·cm(-2)).     

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Exploring the Chemistry of the P-Complexed Parent Phosphine

Abstract

Whereas the parent phosphine is a highly poisonous, easily oxidized gas, a phosphine complex such as W(CO)₅PH₃ is much easier to handle, as this complex is an air stable white solid.     

Analogie Photochimique. II—Cyclisation des Aldéhydes δ,ε Insaturés sous Impact Electronique

The mass spectra of 4, 4-dimethyl δε-unsaturated aldehydes show an ion at m/e 126 which results from the elimination of a neutral olefin directly from the molecular ion. This fragmentation is shown to occur through a cyclohexanone intermediate involving a process whcih has its equivalent in the photochemistry of these aldehydes. The abundance ratios of the unimolecular metastable decompositions of these m/e 126 ions are in excellent agreement with the proposed mechanism.     

Optical preprocessing for texture classification using specialized binary black and white pseudocoloring masks

Image texture is a neighborhood information which is time consuming to analyze by computer. Optical processing can be used as a preprocessor to reveal some of the texture information in parallel on the whole image before classification of the preprocessed image by computer. Pseudocoloring allows an easy discrimination of texture information. A specialized binary black and white mask is introduced which selects at one particular wavelength one peak of the diffracted power spectrum of each texture considered. The method is applicable to textures showing some periodicity. The resolution, selectivity and difficulties of the method are described qualitatively and an experimental example including a problem of partial cross talk between different textures is presented.     

Structure,vibrational study and conductivity of the trihydrated uranyl bis(dihydrogenophosphate): UO2(H2PO4)2·3H2O

The X-ray structure (293 K) of UO₂(H₂PO₄)₂·3H₂O has been refined (R = 0.062): M_r = 518g, space group: P2₁/c (Z = 4); $\text{a = 10.816(1)}\text{A}\text{?}$, $\text{b = 13.896(2)}\text{A}\text{?}$, $\text{c = 7.481(1)}\text{A}\text{?}$, β = 105.65(1)^°, $\text{V = 1082.7(2)}\text{A}\text{?}{}^3$; D_c = 3.17 Mg m^?3. The structure consists of infinite chains along the (101) axis with U atoms bridged by two H₂PO₄ groups. The U atom is surrounded by a pentagonal bipyramid of oxygen atoms, one of them being an equatorial water molecule. The cohesion between the chains is ensured by hydrogen bonds involving the two last water molecules. An assignment of IR and Raman bands with isotopic substitution spectra is proposed. A phase transition at 128 K was made evident by DSC and spectroscopy. The room-temperature phase is characterized by a high disorder of the OH bond orientation while in the low-temperature phase H₂O and POH species appear well oriented. The conductivity seems to occur by proton transfer and protonic-species rotation at the POH-water molecular interface between the chains. ac conductivity has been determined by means of the complex-impedance method ($\text{σ}{}_{\mathrm{<mtext>RT</mtext>}}\text{～ (3?12) × 10}{}^{\mathrm{?5}}\text{Ω}{}^{\mathrm{?1}}\text{cm}{}^{\mathrm{?1}}$; E ～ 0.20 eV).     

Minimal regularity of the solutions of some transmission problems

We consider some transmission problems for the Laplace operator in two‐dimensional domains. Our goal is to give minimal regularity of the solutions, better than H¹, with or without conditions on the (positive) material constants. Under a monotonicity or quasi‐monotonicity condition on the constants (or on the inverses according to the boundary conditions), we study the behaviour of the solution near vertex and near interior nodes and show in each case that the given regularity is sharp. Without condition we prove that the regularity near a corner is of the form H^1+ρ, where ρ is a given bound depending on the material constants. Numerical examples are presented which confirm the sharpness of our lower bounds. Copyright © 2003 John Wiley & Sons, Ltd.     

Crystallization of bisphenol-A polycarbonate induced by organic salts: Chemical modification of the polymer. I. Model reactions

The chemical modifications induced in diphenyl carbonate (DPC) by sodium arylcarboxylates between 200 and 250°C were studied to model the behavior of bisphenol-A polycarbonate – salt systems. Reaction between the salt and DPC produces sodium phenoxide, the phenyl arylcarboxylate corresponding to the salt, and carbon dioxide. The two latter compounds probably result from the decarboxylation of an unstable intermediate compound, viz., a mixed carboxylic carbonic anhydride. CO₂ and sodium phenoxide act as catalysts transforming DPC into phenyl salicylate via the formation of a small amount of sodium salicylate. Electrophilic acylation of sodium phenoxide by DPC is another possible but minor source of phenyl salicylate. Above 250°C, phenyl salicylate becomes unstable and pyrolyzes into o-phenoxybenzoic acid, which is immedicately esterified in the presence of DPC into phenyl o-phenoxybenzoate. In DPC + sodium o-chlorobenzoate systems, reaction between phenyl o-chlorobenzoate and sodium phenoxide is another source of phenyl o-phenoxybenzoate.     

Back to the Local Score in the Logarithmic Case: A Direct and Simple Proof

Let X ₁, ... , X _n be a sequence of i.i.d. integer valued random variables and H _n the local score of the sequence. A recent result shows that H _n is actually the maximum of an integer valued Lindley process. Therefore known results about the asymptotic distribution of the maximum of a weakly dependent process, give readily the expected result about the asymptotic behavior of the local score in the logarithmic case, with a simple way for computing the needed constants. Genomic sequence scoring is one of the most important applications of the local score. An example of an application of the local score on protein sequences is therefore given in the paper.     

Energetics of hydride and electron pair attachment to EX3 (E = B, C, Al, Si and X = F, Cl, Br, I) and the study of bonding trends among EX3, EX3, and EX3H by use of ELF and NBO analyses

A theoretical gas-phase “ligand-free” or “electron pair affinity” (EPA) approach, based on CCSD(T)/(SDB-)cc-pVTZ//MP2/(SDB-)cc-pVTZ electronic structure calculations, is introduced as a possible means for determining Lewis acidity trends among planar EX₃^0/+ (E = B, C, Al, Si; X = F, Cl, Br, I) species. In this treatment, the free electron pair is considered to be an extreme Lewis base. The calculated EPA values are compared with experimental Lewis acidities, previously calculated fluoride ion affinity (FIA) and hydride ion affinity (HA) trends, and are found to exhibit reasonable correlations in all cases. The bonding in the planar and trigonal pyramidal conformations of EX₃^0/+ and of the trigonal pyramidal Lewis base EX₃^2−/− anions are assessed by use of natural bond orbital (NBO) and natural resonance theory (NRT) analyses. The NBO charges of the CX₃⁺ (X = Cl, Br, I, OTeF₅) cations are shown to correlate with the cation-anion and cation-solvent contacts in the recently determined crystal structures of [CCl₃][Sb(OTeF₅)₆], [CBr₃][Sb(OTeF₅)₆]·SO₂ClF, [CI₃][Al(OC(CF₃)₃)₄], and [C(OTeF₅)₃][Sb(OTeF₅)₆]·3SO₂ClF and known fluoro-carbocation structures. Topological electron localization function (ELF) basin lobe isosurfaces and volumes are used to rationalize the Lewis acidity trends and bond ionicities of the EX₃^0/+ species, and Lewis basicities of the EX₃^2−/− species.