Small-angle neutron scattering contrast variation on magnetite-myristic acid-benzene magnetic fluid

A magnetic fluid with magnetite dispersed in D-benzene and stabilized by myristic acid is investigated using the contrast variation technique in small-angle neutron scattering. The results obtained are interpreted within a new approach to the basic functions for polydisperse multicomponent and superparamagnetic systems. Myristic acid is considered an alternative to oleic acid, which is commonly used in these fluids. The parameters characterizing the particle size distribution function and the thickness of the myristic acid layer are determined. The data obtained are in good agreement with the results derived from previous investigations with the use of polarized neutrons.     

Mechanosynthesis of nanocrystalline MgFe2O4—neutron diffraction and Mössbauer spectroscopy

The evolution of nanocrystalline n-MgFe₂O₄ by high-energy milling a mixture of MgO and α-Fe₂O₃ for periods of between 0 h and 12 h has been investigated by neutron diffraction in addition to previous Mössbauer, XRD and HRTEM measurements. Complete transformation of the milled products to n-MgFe₂O₄ only occurs on milling to ～8 h even though the average particle size decreases to <?～10 nm after milling for 2 h. The applied field Mössbauer spectra of n-MgFe2O4 can be well described by two subspectra representing core and shell regions with different cation distributions and spin canting angles. The neutron pattern of nanocrystalline MgFe₂O₄ is described well by two components comprising nanoparticles of core and shell dimensions ～7(1) nm and ～0.7(1) nm, respectively, in support of the Mössbauer core-shell model.     

Synthesis, growth and optical spectroscopy studies of BaBiBO4 and CaBi2B2O7 crystals

Single-crystalline species of the novel compounds BaBiBO₄ and CaBi₂B₂O₇ with Pna2₁ structure were successfully grown by the top-seed solution growth (TSSG) method and solid-state recrystallization, respectively. X-ray diffraction methods were used to confirm the symmetry of the crystal structure and to determine unit cell parameters. Normal-mode classification and assignment were performed from the results of polarized Raman and IR absorption measurements on the obtained crystals. The high-frequency part of the vibrational spectra of both materials (580–1400 cm^?1) is reminiscent of the normal modes of the isolated [BO₃]^3? group. The expected crystal-field induced changes in these modes from group-theoretical considerations provide important clues for the normal-mode assignment of the high-frequency spectral lines.     

Ion exchange reactions of NaSbO3 and morphotropic series MSbO3

By reactions of ilmenite-type NaSbO₃ with molten nitrates at ca. 300 °C, ilmenite forms of AgSbO₃ and TlSbO₃ have been obtained and characterized by chemical analysis and X-ray diffraction (rhombohedral, a=5.3272(9) and 5.3149(7) Å, c=16.6923(2) and 21.5136(4) Å, respectively). Unexpectedly, a new form of LiSbO₃, prepared in a similar way, is not rhombohedral. Its XRD pattern has been indexed on a monoclinic C-centred pseudo-orthorhombic cell with a=5.2948(7), b=9.0082(7), c=5.2923(6) Å, β=113.790(5). This cell may be derived from the ilmenite structure by gliding SbO_6/2 layers. Diffuse nature of the XRD pattern is due to stacking faults. TlSbO₃ also contains faults, which have been modelled by 10% 2H stacking analogous to known P-31c polytype. On heating, layered AgSbO₃ and LiSbO₃ transform to stable phases (pyrochlore and Pncn, respectively), but TlSbO₃ remains unchanged at least to 850 °C. Attempts to substitute Cs for Na have been unsuccessful. Previously reported X-ray data for ilmenite-type CsSbO₃ are discredited. Volume relations in the MSbO₃ series are discussed.     

Example of a System Whose Minimal Trajectory Attractor Does not Contain Solutions of the System

Mathematical Notes -     

Dynamic pressure jump in barrier-discharge excilamps

Data for the pressure jump are used to study thermodynamic processes in barrier-discharge excilamps under the conditions of a diffuse (uniform) discharge and microdischarges. It is shown that a linear relationship between the pressure jump and excilamp radiation intensity can help to control the radiation power.     

Electronic Structure and Optical Properties of the Surface F-Centers in MgO: A Theoretical Analysis by DFT Approach

Electronic structure of Mg9O9 and Mg9O8 clusters modeling nano-crystalline powders of magnesium oxide has been analyzed within the frames of the density functional theory (DFT). In the framework of time-dependent DFT method (TD-DFT), the relationship between the surface and bulk properties of nano-crystals is analyzed based on variations in the density of electronic states (DOS) and changes of electronic spectra. The spectroscopy of spatial defects like low-coordinated oxygen ions and of surface point defects like F⁺- and F-centers is investigated. Optical properties of the nano-sized crystalline magnesium oxide are characterized by a spectrum of absorption bands in the range of 1-5 eV. Point defects such as F-centers absorb light in the range of 1.2-1.5 eV. Spatial defects O_LC in nano-crystals generate absorption bands in the range of 2.5-5.0 eV. According to calculations, there is no direct relation between coordination numbers of surface ions and excitation energies. Theoretical excitation energies are compared with experimental optical properties of the F⁺- and F-centers.