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Abstract: Single crystals of CsHo3Te5 and Cs3Tm11Te18 have been grown as byproducts in the synthesis of CsLnZnTe3 (Ln=Ho or Tm) through the reaction of Ln, Zn, and Te with a CsCl flux at 850°C. The crystal structures have been determined from single-crystal X-ray diffraction data. CsHo3Te5 crystallizes in space group Pnma of the orthorhombic system whereas Cs3Tm11Te18 crystallizes in the space group C2/m of the monoclinic system. Each of the compounds adopts a three-dimensional structure; each possesses tunnels built from LnTe6 octahedra that are filled with Cs atoms. The pseudo-rectangular tunnel in CsHo3Te5 is large enough in cross-section to accommodate two symmetrically equivalent Cs atoms. In the Cs3Tm11Te18 structure there are two different sized tunnels: the smaller one is only large enough to host one Cs atom per unit cell whereas the larger one can accommodate two Cs atoms. The electronic structure of CsHo3Te5 was calculated. The band gap is estimated to be about 1.2eV, consistent with the black color of the crystals. [Copyright &y& Elsevier]

Seven new quaternary metal sulfides, KY2CuS4, KNd2CuS4, KSm2CuS4, KTb2CuS4, KHo2CuS4, K2Dy4Cu4S9, and K2Ho4Cu4S9, were prepared by the reactive flux method. All crystallographic data were collected at 153 K. The isostructural compounds KLn2CuS4 (Ln=Y, Nd, Sm, Tb, Ho) crystallize in space group Cmcm of the orthorhombic system with four formula units in cells of dimensions (Ln, a, b, c (A˚)): Y, 3.9475(9), 13.345(3), 13.668(3); Nd, 4.0577(3), 13.7442(10), 13.9265(10); Sm, 4.0218(4), 13.6074(14), 13.8264(14); Tb, 3.9679(5), 13.4243(17), 13.7102(18); Ho, 3.9378(3), 13.3330(11), 13.6487(11). The corresponding R1 indices for the refined structures are 0.0197, 0.0153, 0.0158, 0.0181, and 0.0178. The isostructural compounds K2Dy4Cu4S9 and K2Ho4Cu4S9 crystallize in space group C2/m of the monoclinic system with two formula units in cells of dimensions (Ln, a, b, c (A˚), β (°)): Dy, 13.7061(13), 3.9482(4), 15.8111(15), 109.723(1); Ho, 13.6760(14), 3.9360(4), 15.7950 (16), 109.666(2). The corresponding R1 indices are 0.0312 and 0.0207. Both structure types are closely related three-dimensional tunnel structures. The tunnels are filled with bicapped trigonal-prismatically coordinated K atoms. Their anionic frameworks are built from LnS6 octahedra and CuS4 tetrahedra. KLn2CuS4 contains ∞1[CuS35−] chains of vertex-sharing tetrahedra and K2Ln4Cu4S9 contains ∞1[Cu4S812−] chains of tetrahedra. K2Ho4Cu4S9 shows Curie–Weiss paramagnetic behavior between 5 and 300 K, and has an effective magnetic moment of 10.71 μB for Ho3+ at 293 K. Optical band gaps of 2.17 eV for KSm2CuS4 and 2.43 eV for K2Ho4Cu4S9 were deduced from diffuse reflectance spectra. A first-principles calculation of the density of states and the frequency-dependent optical conductivity was performed on KSm2CuS4. The calculated band gap of 2.1 eV is in good agreement with the experimental value. [Copyright &y& Elsevier]

Abstract: Experimental and theoretical studies of adsorption of methyl on hematite (0001) were carried out using a novel source of the methyl radicals, TPD, AES, QMS, LEED and density functional theory. The crystal surface was not very well characterized experimentally, due to the possible co-existence of several phases and tendency to form magnetite overlayers. Thus observed weak methyl adsorption could be tentatively assigned to defect sites. DFT pseudopotential supercell band structure calculations on clean and adsorbed idealized surfaces predict that the partially oxidized “ferryl structure” has largest adsorption energy, and that regular sites could also adsorb methyl radicals. Embedded-cluster models were used to extract local bonding information and details of electronic structure. [Copyright &y& Elsevier]

Abstract: We have recently reported structure solutions for the (2×1) and c(4×2) reconstructions of SrTiO3(001) based on high-resolution electron microscopy, direct methods analysis of diffraction data and density functional theory. Both reconstructions were found to be TiO2-rich and feature a single overlayer of TiO2 stoichiometry on top of a bulk-like TiO2 layer. Qualitatively, the two reconstruction geometries differ in the cation sub-lattice of the overlayer only, where Ti atoms occupy half of the fivefold cation sites. In the present work we use density functional theory to generate a number of variations of this structural motif in search of patterns of stability. We find a reliable predictor for the reconstruction energy in the ability of oxygen atoms to relax vertically out of the overlayer plane to minimize non-bonded oxygen–oxygen repulsions. Out-of-plane relaxation of oxygen atoms in turn is modulated by the number and relative position of coordinating Ti atoms, which yields simple empirical rules as to how cations are distributed in low energy reconstructions. [Copyright &y& Elsevier]

We report the solution of the c(4 × 2) reconstruction of SrTiO[sub 3] (001), obtained through a combination of high-resolution transmission electron microscopy, direct methods analysis, and density functional theory. The structure is characterized by a single overlayer of TiO[sub 2] stoichiometry in which TiO[sub 5] polyhedra are arranged into edge-shared structures, in contrast to the corner-shared TiO[sub 6] polyhedra in bulk. This structural pattern is similar to that reported by us earlier for the (2 × 1) reconstruction of the same crystal face formed at higher temperature. We discuss probable mechanisms of surface stabilization as revealed by these two solutions which are likely to apply to other reconstructions of SrTiO[sub 3] (001) and, possibly, other perovskites in general. [ABSTRACT FROM AUTHOR]

The article examines the use of Zn2(1,4-benzenedicarboxylate)2(1,4-diazabicyclo[2.2.2]octane) metal-organic frameworks (MOF-1) as an adsorbent for alkane separations. The authors simulated a multicomponent mixture in the C5-C7 range using grand canonical Monte Carlo. The absolute adsorption isotherms predicted for a 13-component alkane mixture in MOF-1 are presented.

Black single crystals of A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) have been synthesized by the reactive flux method. These isostructural compounds crystallize in the cubic space group Ia ̅3d at room temperature. The structure comprises a three-dimensional framework built from US(6) octahedra and CuS(3) trigonal planar units with A cations residing in the cavities. There are no S-S bonds in the structure. To elucidate the oxidation state of U in these compounds, various physical property measurements and characterization methods were carried out. Temperature-dependent electrical resistivity measurement on a single crystal of K(6)Cu(12)U(2)S(15) showed it to be a semiconductor. These three A(6)Cu(12)U(2)S(15) (A = K, Rb, Cs) compounds all exhibit small effective magnetic moments, < 0.58 μ(B)/U and band gaps of about 0.55(2) eV in their optical absorption spectra. From X-ray absorption near edge spectroscopy (XANES), the absorption edge of A(6)Cu(12)U(2)S(15) is very close to that of UO(3). Electronic band structure calculations at the density functional theory (DFT) level indicate a strong degree of covalency between U and S atoms, but theory was not conclusive about the formal oxidation state of U. All experimental data suggest that the A(6)Cu(12)U(2)S(15) family is best described as an intermediate U(5+)/U(6+) sulfide system of (A(+))(6)(Cu(+))(12)(U(5+))(2)(S(2-))(13)(S(-))(2) and (A(+))(6)(Cu(+))(12)(U(6+))(2)(S(2-))(15).

Eleven new quaternary rare-earth tellurides, CsLnZnTe3 (Ln=La, Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, and Y), were prepared from solid-state reactions at 1123 K. These isostructural materials crystallize in the layered KZrCuS3 structure type in the orthorhombic space group Cmcm. The structure is composed of LnTe6 octahedra and ZnTe4 tetrahedra that share edges to form [LnZnTe3] layers. These layers stack perpendicular to [010] and are separated by layers of face- and edge-sharing CsTe8 bicapped trigonal prisms. There are no Te-Te bonds in the structure of these CsLnZnTe3 compounds so the formal oxidation states of Cs/Ln/Zn/Te are 1+/3+/2+/2-. Optical band gaps of 2.13 eV for CsGdZnTe3 and 2.12 eV for CsTbZnTe3 were deduced from single-crystal optical absorption measurements. A first-principles calculation of the density of states and the frequency-dependent optical properties was performed on CsGdZnTe3. The calculated band gap of 2.1 eV is in good agreement with the experimental value. A quadratic fit for the lanthanide contraction of the Ln-Te distance is superior to a linear one if the closed-shell atom is included.