Electronic Structure and Transport Properties of Bi2Te3 and Bi2Se3 Single Crystals.

The electrical resistivity and the Hall effect of topological insulator Bi2Te3 and Bi2Se3 single crystals were studied in the temperature range from 4.2 to 300 K and in magnetic fields up to 10 T. Theoretical calculations of the electronic structure of these compounds were carried out in density functional approach, taking into account spin-orbit coupling and crystal structure data for temperatures of 5, 50 and 300 K. A clear correlation was found between the density of electronic states at the Fermi level and the current carrier concentration. In the case of Bi2Te3, the density of states at the Fermi level and the current carrier concentration increase with increasing temperature, from 0.296 states eV-1 cell-1 (5 K) to 0.307 states eV-1 cell-1 (300 K) and from 0.9 × 1019 cm-3 (5 K) to 2.6 × 1019 cm-3 (300 K), respectively. On the contrary, in the case of Bi2Se3, the density of states decreases with increasing temperature, from 0.201 states eV-1 cell-1 (5 K) to 0.198 states eV-1 cell-1 (300 K), and, as a consequence, the charge carrier concentration also decreases from 2.94 × 1019 cm-3 (5 K) to 2.81 × 1019 cm-3 (300 K).

The interaction of defects in a mayenite structure.

Calcium aluminate Ca12Al14O33 initially known as cement compound after a series of structural refinements presented a complex cubic structure. It demonstrates a surprising feature consisting of the occurrence of spherical cavities named as cages. After this, mayenite is regarded as a kind of anti-zeolite. An alternative representation of such compounds formulated as highly non-stoichiometric garnets is highlighted in the present study. Mayenite is described as non-stoichiometric garnet {Ca3-x□x}1[Ca, Al]2Al3O12-x using the Raman spectroscopy. The dependence of phase diagram Al2O3-CaO in the region near the mayenite composition on the oxygen activity is summarized regarding its structural deficiency. It is pointed that cage is the result of defects association whereas structural defects tend to interact with each other. The main consequence of such interaction is a spontaneous formation of a core-shell structure. It is evidenced by the presence of a near-surface layer of small thickness over a compact oxide. The local symmetry of the mayenite structure at room temperature in oxidized and reduced (electride) state was studied by Raman spectroscopy which revealed the presence of luminescence without the rare-earths' doping.

Oxygen surface exchange and diffusion in mayenite single crystal.

Oxygen surface exchange and diffusion in Ca12Al14O33±Î´ single crystal were studied by a unique in situ method based on isotope equilibration in the gas phase. Although the interphase exchange rate and oxygen diffusion coefficient demonstrate good agreement with available data, only the employed method is efficient to isolate the contributions of various types of exchange; thus, for the first time, it is possible to estimate the surface heterogeneity of mayenite. The obtained results disprove conclusions previously developed in the literature; the temperature region of 750 °C to 850 °C is not the intermediate region where two types of oxygen diffusion coexist. Complex discussion of the accumulated information on the temperature-dependent properties of mayenite allowed us to represent a model describing the observed dependencies based on the near-surface layer stability in the studied temperature range.

Crystal structure of (E)-1-(2,4-di-nitro-phen-yl)-2-[(E)-5-phenyl-1-(p-tol-yl)pent-2-en-4-yn-1-yl-idene]hydrazine.

In the title compound, C24H18N4O4, the plane of the phenyl ring is inclined to those of the toluene ring and the di-nitro-substituted benzene ring by 66.96 (19) and 47.06 (18)°, respectively, while the planes of the two benzene rings are inclined to one another by 36.26 (19)°. There is an intra-molecular N-H⋯O hydrogen bond between the NH group and the O atom of a nitro group, forming an S(6) ring motif. In the crystal, mol-ecules are linked by C-H⋯O hydrogen bonds and C-H⋯π inter-actions, forming a three-dimensional network. There are also weak π-π inter-actions present involving the phenyl ring and the di-nitro-substituted benzene ring [inter-centroid distance = 3.741 (2) Å].

Crystal structure of (2E,4E)-5-[bis-(2-hy-droxy-eth-yl)amino]-1-(4-chloro-phen-yl)-5-phenyl-penta-2,4-dien-1-one.

In the title compound, C21H22ClNO3, the penta-diene unit is nearly planar [maximum deviation = 0.023 (1) Å], but the carbonyl O atom deviates significantly [by 0.304 (1) Å] from its mean plane, which is twisted with respect to the phenyl and chloro-benzene rings by 71.34 (13) and 46.40 (13)°, respectively. In the crystal, inversion-related molecules are linked by two pairs of O-H⋯O hydrogen bonds, forming chains propagating along [01-1], enclosing R (2) 2(16) and R (2) 2(22) ring motifs. The chains are linked via C-H⋯O hydrogen bonds and C-H⋯π inter-actions into a three-dimensional supra-molecular architecture.