Small-Angle X-ray and neutron scattering from diamond single crystals

Results of Small-Angle Scattering study of diamonds with various types of point and extended defects and different degrees of annealing are presented. It is shown that thermal annealing and/or mechanical deformation cause formation of nanosized planar and threedimensional defects giving rise to Small-Angle Scattering. The defects are often facetted by crystallographic planes 111, 100, 110, 311, 211 common for diamond. The scattering defects likely consist of clusters of intrinsic and impurity-related defects; boundaries of mechanical twins also contribute to the SAS signal. There is no clear correlation between concentration of nitrogen impurity and intensity of the scattering.Comment: 6 pages, 5 figures; presented at SANS-YuMO User Meeting 2011, Dubna, Russi

Low temperature mixed spin state of Co3+ in LaCoO3 evidenced from Jahn-Teller lattice distortions

One- and multi-phonon excitations of the single crystalline LaCoO3 were studied using Raman spectroscopy in the temperature region of 5 K - 300 K. First-order Raman spectra show a larger number of phonon modes than allowed for the rhombohedral structure. Additional phonon modes are interpreted in terms of activated modes due to lattice distortions, arising from the Jahn-Teller (JT) activity of the intermediate-spin (IS) state of Co3+ ions. In particular, the 608-cm-1 stretching-type mode shows anomalous behavior in peak energy and scattering intensity as a function of temperature. The anomalous temperature dependence of the second-order phonon excitations spectra is in accordance with the Franck-Condon mechanism that is characteristic for a JT orbital order.Comment: 11 pages, 9 figures, to be published in J. Low. Temp. Physic

X-ray Diffraction Study of Superstructure in GdBaCo2O5.5

A single crystal of GdBaCo2O5.47(2) has been studied by means of X-ray diffraction. Appearance of superstructure reflections at T = 341.5(7) K gives an evidence of continuous transition to the phase with unit cell doubled along the shortest edge a1. Critical exponent for the order parameter is found to be beta=0.33(1). The superstructure reflections are about 2-4 orders of magnitude weaker than the basic ones. Their systematic extinction indicates the crystal symmetry change from Pmmm to Pmma. The integrated intensities allow to calculate displacements of atoms from the positions in the high-temperature phase. The cobalt-ligand distances in the ordered phase are discussed in terms of the spin-state/orbital ordering of Co3+ ions.Comment: 4 page

Extended defects in natural diamonds: Atomic Force Microscopy investigation

Surfaces of natural diamonds etched in high-pressure experiments in H2O, CO2 and H2O-NaCl fluids were investigated using Atomic Force Microscopy. Partial dissolution of the crystals produced several types of surface features including the well-known trigons and hillocks and revealed several new types of defects. Besides well-known trigons and dissolution hillocks several new types of defects are observed. The most remarkable ones are assigned to anelastic twins of several types. The observation of abundant microtwins, ordering of hillocks and presence of defects presumably related to knots of branched dislocations suggests importance of post-growth deformation events on formation of diamond microstructure. This work confirms previous reports of ordering of extended defects in some deformed diamonds. In addition, the current work shows that natural diamonds deform not only by dislocation mechanism and slip, but also but mechanical twinning. The dominant mechanism should depend on pressure-temperature-stress conditions during diamond transport from the formation domain to the Earth surface.Comment: Submitted to special issue (1st European Mineralogical congress, Frankfurt, Germany, September 2012) of European Journal of Mineralogy. 21 page, 9 figure

Influence of Co3+^{3+} spin-state on optical properties of LaCoO3_3 and HoCoO3_3

Optical properties of the isoelectronic compounds LaCoO$_3$ and HoCoO$_3$ has been experimentally and theoretically investigated. We've measured the real $\epsilon_1(\omega)$ and imaginary $\epsilon_2(\omega)$ parts of the dielectric function, reflectance $R(\omega)$ and optical conductivity at room temperature. The shift of the most pronounced spectral features to the high energy region on 0.3 eV associated with larger distortions due to the smaller rare earth ionic radii in HoCoO$_3$ in comparison with LaCoO$_3$ was observed. Also there was found an enhancement of absorption intensity in the range 1.3-2.3 eV in all kinds of spectra in HoCoO$_3$, which can be attributed basing on the results of LDA+U calculations to the different spin-states of Co$^{3+}$ ion in these compounds. The shift of the onset of the absorption from less than 0.1 eV in LaCoO$_3$ to 0.7 eV in HoCoO$_3$ and an absorption intensity enhancement in a narrow spectral range 1.2-2.6 eV in HoCoO$_3$ are clearly seen from the calculated convolution of partial densities of states obtained in the LDA+U approach. Such changes are assumed to be induced by the different Co$^{3+}$ spin-state in these compounds at room temperature.Comment: 10 pages, 3 figure

Temperature excitation of the Co3+ triplet spin-state in LaCoO3 determined by polarized neutron diffraction

The magnetic moment induced by an external magnetic field of 5.8 T on the Co3+ ions in LaCoO3 has been measured by polarized neutron diffraction. Measurements were made at 100 K, near to the spin-state transition, at 1.5 K and at 285 K. The data give evidence for a transition from the ground singlet state (S = 0) to the excited triplet intermediate spin state (S = 1). The energy of K estimated for the high-spin (S = 2) state, is too high to contribute significantly even at T = 285 K. There is evidence for a small negative covalent spin density associated with the oxygen ligands amounting to about one fifth of the aligned Co3+ moment at all three temperatures.Comment: 10 pages, 3 figures, 2 tables, 25 reference

Patients’ attitude towards coercion and violence in providing stationary psychiatric aid: ethical and preventive aspects

To develop recommendations for improving the conditions of stay and treatment of persons with mental disorders in psychiatric clinics based on the study of the frequency and forms of coercion and violence applied to patients, and their personal assessmen