18O/16O ratio measurements of inorganic and organic materials by elemental analysis-pyrolysis-isotope ratio mass spectrometry continuous-flow techniques

We have used a high‐precision, easy, low‐cost and rapid method of oxygen isotope analysis applied to various O‐bearing matrices, organic and inorganic (sulfates, nitrates and phosphates), whose ¹⁸O/¹⁶O ratios had already been measured. It was first successfully applied to ¹⁸O analyses of natural and synthetic phosphate samples. The technique uses high‐temperature elemental analysis–pyrolysis (EA‐pyrolysis) interfaced in continuous‐flow mode to an isotope ratio mass spectrometry (IRMS) system. Using the same pyrolysis method we have been able to generate a single calibration curve for all those samples showing pyrolysis efficiencies independent of the type of matrix pyrolysed. We have also investigated this matrix‐dependent pyrolysis issue using a newly developed pyrolysis technique involving 'purge‐and‐trap' chromatography. As previously stated, silver phosphate being a very stable material, weakly hygroscopic and easily synthesized with predictable ¹⁸O/¹⁶O values, could be considered as a good candidate to become a reference material for the determination of ¹⁸O/¹⁶O ratios by EA‐pyrolysis‐IRMS. Copyright © 2011 John Wiley & Sons, Ltd.     

Pyroelectric properties of an antiferroelectric liquid crystal

The effects of temperature and applied voltage on the pyroelectric properties of an antiferroelectric liquid crystal are given. It has been found that the pyroelectric signal depends strongly on the bias voltage across the sample. The pyroelectric signal behaviour is interpreted with the aid of spontaneous polarization data and good agreement is found between the results from the pyroelectric and polarization techniques. The spontaneous polarization of the sample exhibits the temperature- and field-induced `Devil's staircase' behaviour, as predicted by the Ising model.     

A review of self-organising 2,5- and 2,4-disubstituted 1,3-thiazole-containing materials: synthesis,mechanisms and tactics

ABSTRACT

2,5- and 2,4-disubstituted 1,3-thiazoles have been incorporated as core units in thermotropic liquid crystalline materials. However, synthetic approaches to these systems have been somewhat limited, and this is reflected in the relatively few reports of these mesogenic systems. This paper highlights both recent and well-established synthetic approaches to these systems using ring closure (Gabriel- and Hantzsch-type approaches) methodology and modifications of an intact 1,3-thiazole ring. The scope and limitations of each of these approaches are discussed.     

Nature of the Arsonium‐Ylide Ph3As=CH2 and a Uranium(IV) Arsonium–Carbene Complex

Treatment of [Ph₃EMe][I] with [Na{N(SiMe₃)₂}] affords the ylides [Ph₃E=CH₂] (E=As, 1As ; P, 1P ). For 1As this overcomes prior difficulties in the synthesis of this classical arsonium‐ylide that have historically impeded its wider study. The structure of 1As has now been determined, 45 years after it was first convincingly isolated, and compared to 1P , confirming the long‐proposed hypothesis of increasing pyramidalisation of the ylide‐carbon, highlighting the increasing dominance of E⁺?C^? dipolar resonance form (sp³‐C) over the E=C ene π‐bonded form (sp²‐C), as group 15 is descended. The uranium(IV)–cyclometallate complex [U{N(CH₂CH₂NSiPrⁱ₃)₂(CH₂CH₂SiPrⁱ₂CH(Me)CH₂)}] reacts with 1As and 1P by α‐proton abstraction to give [U(Tren^TIPS)(CHEPh₃)] (Tren^TIPS=N(CH₂CH₂NSiPrⁱ₃)₃; E=As, 2As ; P, 2P ), where 2As is an unprecedented structurally characterised arsonium‐carbene complex. The short U?C distances and obtuse U‐C‐E angles suggest significant U=C double bond character. A shorter U?C distance is found for 2As than 2P , consistent with increased uranium‐ and reduced pnictonium‐stabilisation of the carbene as group 15 is descended, which is supported by quantum chemical calculations.     

Luminescence from Ce in sol–gel SiO2

The sol–gel process provides an attractive low temperature alternative to the melt process for producing Ce-doped silica, but reports of the emission wavelength have not been consistent. In this paper, luminescence measurements using a variety of excitation methods, including cathodoluminescence not yet reported by other researchers, are compared and evaluated in the light of previously published data. Several papers report luminescence around 350 nm but emission near this wavelength was not found from our samples. This luminescence originates from Ce that has not yet been incorporated in the silica and is found in samples that have not undergone high temperature annealing. Our photoluminescence results from samples annealed in a reducing atmosphere suggest that emission from Ce incorporated in the silica lattice occurs near 455 nm, and some indication of the emission from Ce in amorphous clusters at 400 nm is also found. However, our results also confirm earlier indications that intrinsic defects in silica can create photoluminescence near both these wavelengths, which can make identification of the luminescence due to Ce difficult. Finally, it has been found that samples which have been annealed in air, and therefore display poor photoluminescence because most of the Ce occurs in the tetravalent form, are luminescent under electron beam excitation. It is suggested that during cathodoluminescence measurements Ce⁴⁺ ions capture electrons to form excited Ce³⁺ ions from which the luminescence originates.     

New bent core mesogens with exceptionally high clearing points

A homologous series of novel two-ring alkoxythiophene-containing liquid crystals has been synthesized using a recently developed cyclization methodology to construct the heterocyclic core. The new heterocyclic unit is expected to confer high negative dielectric anisotropy and high dielectric biaxiality when incorporated into suitable mesogenic structures. The materials reported here possess nematic phases, with the longer chain homologues displaying smectic mesomorphism. In all cases the clearing points are significantly enhanced when compared with other two-ring thiophene-based mesogens. The synthesis, mesomorphic behaviour and stability are discussed, and the mesomorphic behaviour is compared with the analogous 4-alkoxy-4′-cyanobiphenyl derivatives synthesized by Gray.     

Microwave characteristics of high Tcsuperconducting coplanar waveguide resonator

A theoretical formulation has been developed to calculate the coupling coefficient, London penetration depth, and surface resistance of a coplanar waveguide resonator fabricated from films of superconducting YBCO material. Experimental data of the reflection coefficient as a function of temperature and frequency agree reasonably well with calculations. The formulation is of sufficient generality to be applicable to other guided structures     

Three-dimensional holographic lithography by an iterative algorithm

We have applied an iterative algorithm for hologram design with multiple output image planes arranged in close proximity to create continuous patterns within an imaging volume. These holograms have been designed for photolithography on three-dimensional surfaces. The influence of simulated image plane separation on the final image, and its suitability for lithography, is assessed. Results are presented and the most suitable case is demonstrated experimentally.     

synthesis,phase transitions and optical properties of novel tetrathiafulvalene derivatives with extremely high molecular polarizabilities

The synthesis of novel unsymmetrically-substituted tetrathiafulvalene derivatives based on lithiation procedures is described. The disubstituted derivatives were synthesized as 1:1 cis/trans-isomeric mixtures, the compositions of which were established by ¹H NMR and ¹³C NMR spectroscopy. The transition temperatures, refractive indices, birefringence, polarizability and order parameter of each of the mixtures were determined and the values are discussed in comparison with analogous compounds with the tetrathiafulvalene unit replaced by a 1,4-phenylene group. In addition, we describe the synthesis of a number of monosubstituted tetrathiafulvalene derivatives and their associated thermal properties. The isomeric compounds presented in this paper have exceptionally large values of polarizability anisotropy, as compared with their phenyl-containing counterparts.