Magnetism and optical properties of nanocrystalline Cu<Subscript>2</Subscript>O and TiO<Subscript>2</Subscript> powders

The optical spectra of Cu₂O and TiO₂ nanopowders have been studied, which contain information about structural defects and are of interest in the search for optimum regimes providing the synthesis of ferromagnetic nanocrystals with Curie temperatures above room temperature.     

Low temperature phase transition in ZnSe doped with nickel

Neutron diffraction and ultrasonic experiments as well as measurements of heat conductivity in ZnSe and Zn_1−xNi_xSe (x=0.0025) semiconductors have been carried out. As a result, a structural transition induced by Ni impurity has been found at      

Absorption line CW EPR using an amplitude modulated longitudinal field

In standard continuous wave electron paramagnetic resonance (CW-EPR) experiments, the first derivative of absorption lines is detected. This type of a line shape is caused by the magnetic field modulation and is usually an undesired feature, since the sensitivity of CW-EPR drastically decreases with increasing linewidth. A new approach is introduced, which allows for the measurement of absorption line EPR spectra in systems with broad inhomogeneous lines. The method makes use of multiple-photon transitions that are induced in spin systems when a transverse microwave and a longitudinal radio frequency field are simultaneously applied. The absorption lines are obtained by using amplitude modulation of the radio frequency field and slight saturation of the spectral lines. The basics of the new approach are discussed and experimental examples are given.     

Specific features of the phonon thermal conductivity of II–VI compound semiconductors doped with 3<Emphasis Type="Italic">d</Emphasis> transition metal ions

The phonon thermal conductivity of II–VI compound semiconductors doped with 3d transition metal ions is studied. The observed temperature anomalies are analyzed in terms of the dynamic Jahn-Teller effect.     

A comparative study on the acylative kinetic resolution of racemic fluorinated and non-fluorinated 2-methyl-1,2,3,4-tetrahydroquinolines and 3,4-dihydro-3-methyl-2H-[1,4]benzoxazines

The acylative kinetic resolution of racemic 6-fluoro-2-methyl-1,2,3,4-tetrahydroquinoline, 7,8-difluoro-3,4-dihydro-3-methyl-2H-[1,4]benzoxazine, and their non-fluorinated analogues with (S)-naproxen and N-phthaloyl-(S)-amino acyl chlorides has been carried out. It has been shown that the presence of fluorine atoms in the aromatic fragment of a heterocyclic amine results in the increasing stereoselectivity of acylation with (S)-naproxen acyl chloride and in a decrease in the efficiency of acylative kinetic resolution using N-phthaloyl-(S)-amino acyl chlorides. A method for the preparation of enantiopure (S)-6-fluoro-2-methyl-1,2,3,4-tetrahydroquinoline (ee >99%) was developed.     

Mesomorphic azomethine complexes of Iron(III) based on 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-2-aminopyridine

A new series of liquid crystalline (LC) complexes Fe(III) based on azomethine 4,4′-dodecyloxybenzoyloxybenzoyl-4-salicylidene-2-aminopyridine with counter-ions PF₆^?, NO₃^?, Cl^?, BF₄^?, ClO₄^?, CNS^? and SO₄^2– was synthesised. According to elemental analysis, FT-IR, ¹H-NMR and mass spectrometry (MALDI ToF), it was found that bi(ligand) Fe(III) complexes were formed with octahedral packing of the metal ion. The presence of the counter-ion in the complexes was confirmed by Infrared spectroscopy. The thermotropic LC properties were investigated by differential scanning calorimetry (DSC) and polarising optical microscopy (POM). All the seven complexes in this series exhibit thermotropic mesophases.     

Study of the formation kinetics of Metastable phases in quenched Al-Mg-Si Alloys

The results of the experimental study of the formation kinetics of metastable phases during decomposition of supersaturated solid solutions of quenched Al-Mg-Si alloys are presented. The process has been studied by measuring the electrical conductivity at low temperatures (18–85°C) and by measuring the Young’s modulus using the acoustic method in the temperature range 120–220°C. The method of measuring the Young’s modulus is characterized by a high precision and has made it possible to distinguish between the successive stages of the decomposition due to the formation of Guinier-Preston zones, particles of the pre-β″/β″ and β′-phases. The effective activation energies have been calculated using the obtained data on the characteristic durations of the stages of the process at different temperatures. It has been shown that the activation energy of the formation and evolution of particles in the β″-phase is considerably lower than the activation energy of diffusion of alloying element atoms at equilibrium conditions, which is caused by the effect of long-lived quenching vacancies. This energy is close to the activation energy of migration of the ν + Mg complex and, according to the obtained results, is equal to 0.58 eV.