Optical properties of a nematic liquid crystal with small refractive index and small birefringence were studied. The ordinary and extraordinary refractive indices and birefringence were measured as functions of temperature by using an Abbe refractometer and wedge nematic cells. From values of these indices the nematic orientational order parameter was calculated by using several methods and corresponding mathematical models. Kuczyński et al. method was found to be suitable for determining the order parameter also for materials featuring small ordinary refractive index, with unknown density.

Measurements of magnetotransport in SnTe/PbTe heterojunctions grown by the molecular beam epitaxy technique on (001) undoped CdTe substrates were performed. At low magnetic fields, quantum corrections to conductivity were observed that may be attributed to the presence of topological states at the junction interface. For a sample with a 5-nm-thick SnTe layer, the data analysis suggests that midgap states are actually gapped. However, the phase coherence effects in 10 and 20 nm SnTe/PbTe samples are fully explained assuming the existence of gapless Dirac cones. Magnetotransport at higher magnetic fields is described in the framework of mobility spectrum analysis (MSA). We demonstrate that the electron- and holelike peaks observed simultaneously for all SnTe/PbTe heterojunctions may originate from the concave and convex parts of the energy isosurface for topological states—and not from the existence of quasiparticles both carrying negative and positive charges. This interpretation is supported by numerical calculations of conductivity tensor components for gapless (100) Dirac cones, performed within a classical model and based on the solutions of the Boltzmann transport equation. Our approach shows the feasibility of MSA in application to magnetotransport measurements on topological matter.

Wedge cells of small apex angle, filled with liquid crystals, were used to determining optical characteristics as functions of temperature for three liquid crystalline mixtures recently produced and a reference nematic. The interference fringes appearing in polarised monochromatic light (of sodium yellow line) normally incident on the cell were exploited to measure the ordinary and extraordinary refractive indices in the reflection mode and birefringence in the transmission mode. The measurements were repeated using Abbe's refractometer for 6CHBT as the reference to verifying the precision. Additionally the order parameter was computed from birefringence as a function of temperature. The results confirm the usefulness of the method and provide the properties of two nematic liquid crystals of small and large birefringence and one smectic liquid crystal of medium birefringence, recently produced. The experimental systems served also to investigating phase transition between the liquid crystals and the isotropic liquid at near-clearing temperature.

An efficient, quick and pretty accurate interference method for determining dispersions of ordinary n _o and extraordinary n _e refractive indices and optical anisotropy of nematic liquid crystals, i.e., n_e(λ), n_o(λ) and Δn(λ) ≡ n _e (λ)–n_o(λ), as functions of wavelength λ (in visible and near infrared region), is presented. The method relies on measurements of positions of interference fringes in spectrogram produced by a flat-parallel nematic liquid crystal cell in only one run.

Possible influence of a nematics splay-bend elastic constant and corresponding free energy functional term on adequacy of description of nematics states is studied by comparing results of theoretical considerations and computer simulations with experimental data. Planar deformation states enforced in flat nematics cells by symmetric aligning cover coatings and external electric or magnetic fields are studied in one-dimensional approximation. Nematics material parameters and nematics-substrate coupling characteristics are determined from experimental data by immediate measurement or by solving inverse problems. Two series of cells with thicknesses between twenty and forty-four micrometers (in fact two wedge cells) with two different orienting substrates are investigated by measuring a cell optical response in a birefringence experimental system. Good agreement between optical retardation measured and simulated is observed. Posterior comparison of free energy contributions from substrate interactions and a hypothetical surface-like term leads to a conclusion that the last one together with a splay-bend elastic constant should be very small and can be neglected.

Nanocrystalline boehmite (gamma-aluminium-oxyhydroxide) is a material of industrial importance, the functionality of which follows from its crystalline microstructure. A procedure for preparing boehmite nanoparticles, comprising the formation of a precipitate by the alkalization of an aqueous solution of aluminium nitrate and subsequent hydrothermal aging, was previously elaborated. The application of an additive (maltitol or tartaric acid) to control the sizes and shapes of crystallites in the produced polycrystalline powder of boehmite was developed. The aim of this work is a study of the effect of the hydrothermal treatment time on nanocrystalline characteristics of boehmite, both in absence and in presence of the additive. The obtained materials were investigated by using X-ray diffraction (XRD) as principal technique and additionally by scanning and transmission electron microscopy. The multi-peak analysis of powder XRD patterns was applied to determine the prevalent crystallite shape, volume-weighted crystallite size distribution, and second-order crystalline lattice strain distribution being principal quantitative characteristics of the crystalline microstructure. Based on these characteristics, three types of the microstructure correlated with the production procedures were observed and discussed in detail. The nanoparticles of boehmites were found to be monocrystalline grains with characteristic habits and sizes of order of ten nanometers weakly dependent on the hydrothermal treatment time.