An experimental study of the smectic A-smectic C transitions in monolayer, partially bilayer and bilayer systems

The smectic A-smectic C (A-C) transition in several compounds has been shown to be mean-field-like (MF) with a substantial tricritical crossover effect. However, a simple MF behaviour, i.e., with negligible tricritical influence, had not been reported till recently. The heat capacity measurements of the MIT group in two compounds exhibiting the bilayer A2-C2 transition revealed such a behaviour. It is of interest to investigate whether a simple MF behaviour can be observed for partially bilayer AdminusCd and monolayer A1-C1 transitions also. We report the first systematic order parameter measurements in the vicinity of the A2-C2, Ad-Cd and A1-C1 transitions. The data analysed in terms of power law and extended mean field expressions provide clear evidence of a simple MF behaviour in all three cases. The significance of this result is discussed

Electromechanically active pair dynamics in a Gd-doped ceria single crystal

Oxygen-defective ceria, e.g. Gd-doped ceria, shows giant electromechanical properties related to a complex local rearrangement of its lattice. Although they are not entirely identified, the electroactive mechanisms arise from cation and oxygen vacancy (V-O) pairs (i.e. Ce-V-O), and the local structural elastic distortion in their surroundings. Here, we study the geometry and behaviour of Ce-V-O pairs in a grain boundary-free bulk Ce0.9Gd0.1O1.95 single crystal under an AC electric field of ca. 11 kV cm(-1). The analysis was carried out through X-ray absorption spectroscopy (XAS) techniques at the Ce L-III edge. Using Density Functional Theory (DFT) calculations, we investigated the effects of the strain on density of states and orbitals at the valence band edge. Our research indicates that electrostriction increases at low temperatures. The electromechanical strain has a structural nature and can rise by one order of magnitude, i.e., from 5 x 10(-4) at room temperature to 5 x 10(-3) at -193 degrees C, due to an increase in the population of the electrically active pairs. At a constant V-O concentration, the material can thus configure heterogeneous pairs and elastic nanodomains that are either mechanically responsive or not

Effect of a rigid nonpolar solute on the splay, bend elastic constants and on rotational viscosity coefficient of 4-4^\prime -n-octyl-cyanobiphenyl

The effect of a rigid nonpolar non-mesogenic solute, ``biphenyl'' which is (C_{6}H_{5}-C_{6}H_{5}), on the splay and bend elastic constants and on the rotational viscosity coefficient of (4,4^{\prime})-n-octyl-cyano biphenyl (8CB) is reported. The experiments involve the measurement of voltage dependence of capacitance of a cell filled with the mixture. Anomalous behavior of both (K_{11}) and (\Delta \epsilon) near the (N-S_{A}) transition have been observed.Comment: RevTeX - 8 figures. Accepted to be published in Physical Review