Ternary Chalcogenides GeSb2Se3 and Ge3Sb4Se7 Containing a ∞1[Sb2Se2]2- 1D Chain and a 2D Structure Related to SnSe.

Ternary chalcogenides, GeSb2Se3 and Ge3Sb4Se7, were synthesized and characterized. These chalcogenides are the first ternary selenides in a ternary Ge-Sb-Se system that feature a layer structure related to black phosphorus and SnSe-type structures. Both compounds contain a ∞1[Sb2Se2]2- unit with Sb+ cations in a zigzag Sb-Sb chain structure, and Sb3+ cations in a distorted NaCl100-type of ∞1[Gen-2Sb2Sen]2+ unit (n = 4, 5). These materials exhibit n-type semiconducting properties with thermal conductivity significantly lower than that of GeSe and Sb2Se3, which could be correlated to the 1D Sb+ chain and disordered sites with different Ge/Sb compositions. It is anticipated that these newly discovered ternary chalcogenides may provide unique properties with enhanced thermoelectric properties.

Ba3TM2Se9 (TM = Nb, Ta): synthesis and characterization of new polyselenides.

New ternary polyselenides Ba3TM2Se9 (TM = Nb, Ta) were synthesized through a solid-state reaction, and their structures were characterized using single-crystal X-ray diffraction. These compounds crystallized into a new structural type with a monoclinic space group P21/c. The structures were constructed from distorted, close-packed layers of ∞3[BaSe3]3.33­ that incorporated TM atoms at octahedral sites and contained [(TM5+)2(Se2­)7(Se22­)] units. Diffuse reflectance spectra and electronic resistivity measurements indicated semiconducting properties and optical band gaps of 1.3 eV for Ba3Nb2Se9 and 1.6 eV for Ba3Ta2Se9. Raman spectra were used to investigate the interatomic interactions. Calculations of the electronic structure verified the semiconducting behavior and bonding interaction of short Se­Se contacts.

Multinary selenides with unusual coordination environment of bismuth.

New multinary selenides Ae3SnPn2Se8 (Ae = Sr, Ba; Pn = Sb, Bi), Sr8.01Ge2.04Bi7.95Se24, and Sr8YGe2Bi7Se24 were synthesized by solid-state reaction, and their structures were determined by single-crystal X-ray diffraction. These compounds crystallize in orthorhombic space group Pnma (no. 62) for Ae3SnPn2Se8 (Ae = Sr, Ba; Pn = Sb, Bi) and in Pna21 (no. 33) for Sr8.01Ge2.04Bi7.95Se24 and Sr8YGe2Bi7Se24. The structures feature one-dimensional corner sharing tetrahedral (∞)(1)[MSe3] units, and one-dimensional edge sharing octahedral ∞1[M4Se10], packed with the alkaline earth or rare earth cations. Sr8.01Ge2.04Bi7.95Se24 and Sr8YGe2Bi7Se24 contain a triple cell superlattice structure derived from a special arrangement of Bi and Ge in the tetrahedrally coordinated ∞1[MSe3] chain. Diffuse reflectance spectra and electronic resistivity measurements indicate semiconducting behaviors; the Sr8YGe2Bi7Se24 Seebeck coefficient is −180 µV/K at 303 K. Electronic structure calculations confirm that the electron count for Sr8YGe2Bi7Se24 is optimal for interatomic bonding in the ionic network.

Synthesis and phase width of quaternary selenides Pb4In(x)M(6-x)Se13 (M = Bi, x = 2.1-2.8; Sb, x = 2).

Quaternary selenides of Pb(4)In(x)M(6-x)Se(13) (M = Bi, x = 2.1-2.8; Sb, x = 2) were synthesized by solid-state methods, and their structures were determined from X-ray diffraction of single crystals. These compounds are isostructural with Pb(4)In(2)Bi(4)S(13) and crystallize in orthorhombic space group Pbam (No. 55) with Z = 4; the structure features a three-dimensional framework consisting of Z-shaped ribbon units and corner-sharing infinite one-dimensional [InSe(4)](infinity) chains running parallel to the c-axis, which are connected by Pb atoms to form a three-dimensional structure. Calculations of the band structure and measurements of Seebeck coefficient, electrical conductivity, and diffuse reflectance spectra confirm that these compounds are semiconductors with a narrow band gap. All compounds show semiconducting properties; the Seebeck coefficient of Pb(4)In(2.5)Bi(3.5)Se(13) is -180 microV/K at 295 K.

Oxidative steam reforming of ethanol over M x La2-x Ce1.8Ru0.2O7-δ (M = Mg, Ca) catalysts: effect of alkaline earth metal substitution and support on stability and activity.

Alkaline earth metal substitutions on the A-site of pyrochlore oxide M x La2-x Ce1.8Ru0.2O7-δ (M = Mg, Ca) were studied as catalyst materials for oxidative/autothermal steam reforming of ethanol (OSRE/ATR). The as-prepared oxides were synthesized by a combustion method and characterized using powder X-ray diffraction (PXRD), and X-ray photoelectron and absorption spectroscopy (XPS and XAS). PXRD Rietveld analysis and elemental analysis (ICP-AES) support the formation of a pyrochlore-type structure (space group Fd3̄m) with a distorted coordination environment. The substitution of Mg2+ and Ca2+ ions affects the oxidation states of Ce4+/3+ and Ru n+ ions and creates oxygen vacancies, which leads to enhanced catalytic activity and reduced ethylene selectivity. A long-term stability test showed optimized catalysts Mg0.3La1.7Ce1.8Ru0.2O7-δ and Ca0.2La1.8Ce1.8Ru0.2O7-δ with S H2 = 101(1)% and S H2 = 91(2)% under OSRE conditions. The initial operation temperatures were lower than that of the unsubstituted catalyst La2Ce1.8Ru0.2O7-δ . Catalysts supported on La2Zr2O7 showed stable OSRE/ATR performance and low carbon deposition compared to catalysts supported on Al2O3. We ascribe the enhanced activity to well-dispersed alkaline earth metal and Ru ions in a solid solution structure, synergistic effects of (Mg, Ca)2+/Ce3+/4+/Ru n+ ions, and a strong catalyst-support interaction that optimized the ethanol conversion and hydrogen production.

A quaternary germanium(II) phosphate, Na[Ge(4)(PO(4))(3)].

A new germanium(II) phosphate, sodium tetra-germanium tris-(phosphate), Na[Ge(4)(PO(4))(3)], has been synthesized by a solid-state reaction. The compound is isotypic with A[Sn(4)(PO(4))(3)] (A = Na, K, NH(4)). It features a [Ge(4)(PO(4))(3)](-) framework made up of GeO(3) pyramids and PO(4) tetra-hedra, which are linked by shared corners, yielding a three-dimensional structure. The crystal studied showed partial inversion twinning.

Relaxation dynamics and structural characterization of organic nanoparticles with enhanced emission.

With a reprecipitation method, we prepared fluorescent organic nanoparticles of 1,4-di[(E)-2-phenyl-1-propenyl]benzene (PPB) that feature weak emission in solution but exhibit blue-shifted absorption and strong emission as aggregates. Picosecond fluorescent transients of these PPB nanoparticles showed biexponential decay, described with a consecutive kinetic model involving two emissive states. X-ray diffraction patterns of PPB nanocrystals indicate long-range packing structures of two types, one the same as in a single crystal and the other not yet determined. PPB molecules in a crystal show an arrangement of a herringbone type with three benzene rings in a PPB unit being nearly planar and two methyl groups of the unit pointing along the same direction, in contrast to the twisted structure of an isolated PPB molecule. Fluorescence transients of PPB on a femtosecond scale indicate an efficient channel for isomerization that is activated for free PPB in solution but inhibited in PPB forming nanoparticles, demonstrating the significance of molecular geometry and twisting motions that affect the relaxation dynamics in the excited state. The versatile techniques combined in this work provide strong evidence to improve our understanding of optical properties in organic nanoparticles dependent on size.

Vacancy Ordering and Bonding Competition in the Group 9 Tellurides M(x)()Te(2) (M = Rh, Ir; 0.75

The Rh-Te and Ir-Te binary systems for 50-78 atom % Te show remarkable differences in their phase and structural features at temperatures below 1100 degrees C. Extended Hückel calculations are employed to investigate the influence of various orbital interactions on these differences. In general, a strong interrelationship among valence electron count, orbital characteristics at and near the Fermi levels, and relative strengths of M-Te, Te-Te, and M-M orbital interactions control the occurrence and structures of various M(x)()Te(2) compounds (0.75 /= (1)/(2)) to emphasize the occurrence of linear Rh(3) units in their structures. The pattern of vacancies in these structures follows the preference of Rh(4)(n)()(+3) oligomers over Rh(4)(n)()(+1) chains. Charge-iterative calculations of Rh atomic orbital energies in Rh(1+)(x)()Te(2) (x = 0.0, 0.5, 1.0) were carried out to analyze the electronic properties of Rh throughout the series. As x increases, Rh-Te orbital interactions become less attractive and the concentration of Rh-Rh repulsive interactions grows. Both effects control the maximum value of x (observed to be 0.84) for this series and influence the pattern of occupied octahedral holes in the close-packed tellurium matrix.

A novel tunable green- to yellow-emitting ß-YFS:Ce³+ phosphor for solid-state lighting.

A Ce(3+)-activated fluorosulfide phosphor (ß-YFS:Ce(3+)) was synthesized by solid-state reaction in a sealed tube. The crystal structure has been refined from the XRD profiles and there are two different crystallographic rare earth sites, namely, Y(1) and Y(2), where the Ce(3+) ions occupied. The emission band with a maximum at 495 nm of ß-Y(0.99)Ce(0.01)FS phosphor was characterized by the 4f-5d transitions of Ce(3+) ion. With increasing Ce(3+) concentration, the emission variations were observed from 495 to 547 nm. When ß-YFS:Ce(3+) phosphors were utilized to incorporate with n-UV/blue chip, greenish-white light with color rendering index of 65-77 were obtained. The results indicate that the tunable green- to yellow-emitting ß-YFS:Ce(3+) can serve as a potential phosphor for incorporation in fabrication for solid-state lighting. The preparation, spectroscopic characterization, quantum efficiency, thermal-quenching behavior, and related LED device data are also presented.

Enhanced catalytic activity of Ce(1-x)M(x)O2 (M = Ti, Zr, and Hf) solid solution with controlled morphologies.

Ce(1-x)M(x)O(2) (M = Ti, Zr, and Hf) nanomaterials with controlled morphology and composition were synthesized by a two-step route for the first time. These nanomaterials exhibit high activities for hydrogen reduction and ethanol reforming reactions, and therefore, they may be useful for applications in catalysis and solid oxide fuel cells.

Effect of the transition metal on the synthesis of quaternary sulfides MPb8In17S34 (M = Cu, Ag, Au).

Quaternary sulfides MPb8In17S34 (M = Cu, Ag, Au) were synthesized at 1123 K from their elements in stoichiometric ratios. These compounds crystallize in monoclinic space group P2(1)/m. The crystal structures feature combinations of 2[InS2] (NaCl111-type) and [MPb2In3S6] (NaCl100-type) slabs. These compounds are semiconductors with band gaps near 1.3 eV.

Synthesis and thermal decomposition of Zn(tda)H2O [tda = S(CH(2)COO)2(2-)].

A novel two-dimensional coordination polymer Zn(tda)H2O [tda = S(CH(2)COO)2(2-)] was synthesized under hydrothermal conditions. The compound crystallized in monoclinic space group P2(1) with a = 16.4154(17) A, b = 5.2133(6) A, c = 16.4210(17) A, beta = 114.165(2) degrees , V = 1282.1(2) A3, and Z = 8. The structure features two-dimensional, noncentrosymmetric networks with a pseudohexagonal network of Zn2+ coordinated by tda and water molecules. Zn(tda)H2O decomposed at T > 300 degrees C to form a ZnO sponge with a surface area approximately 40 m2/g, which makes it an attractive precursor for nanoporous ZnO.

Zr(11)Sb(18): a new binary antimonide exhibiting an unusual Sb atom network with nonclassical Sb-Sb bonding.

The herewith-introduced antimonides Zr(11)Sb(18) and Zr(10.4)V(0.6)Sb(18) were prepared by high-temperature techniques; both arc-melting and solid-state reactions at 1200 degrees C starting from alpha-ZrSb(2) and the metals Zr and V in powder form are possible methods. These isostructural compounds represent an unprecedented metal:antimony ratio of 11:18 and form a new structure type. Zr(11)Sb(18) crystallizes in the tetragonal space group I(-)42d, with the lattice dimensions a = 676.94(4) pm and c = 6007.3(5) pm, while the V-containing phase forms a slightly smaller unit cell with a = 676.48(8) pm and c = 6005.6(9) pm (Z = 4). Their structures are comprised of an Sb atom substructure with several intermediate Sb-Sb bonds starting at 311 pm, which is reminiscent of that found in the series (Ti,M)(5)Sb(8) (M = Zr, Hf, Nb, Mo) published last year. Interwoven with this network is the Zr atom network, which forms a diamond-like metal atom substructure with long Zr-Zr contacts of ca. 360 pm. Band structure calculations based on the linear muffin tin orbital approach reveal these antimonides to be mainly stabilized by strong M-Sb and intermediate Sb-Sb bonds, and additionally--to the smallest extent--by M-M bonds (M = Zr, V). In agreement with the electronic structure calculations, Zr(11)Sb(18) is metallic with a small positive Seebeck coefficient.

The s-p bonded representatives of the prominent BaAl4 structure type: a case study on structural stability of polar intermetallic network structures.

This work presents a detailed, combined experimental and theoretical study on the structural stability of s-p bonded compounds with the BaAl4 structure type (space group I4/mmm, Z = 2) as part of a broad program to investigate the complex questions of structure formation and atomic arrangements in polar intermetallics. From ab initio calculations employing pseudopotentials and a plane wave basis set, we extracted optimized structural parameters, binding energies, and the electronic structure of the systems AeX(III)4, AeX(II)2X(IV)2, AeX(II)2X(III)2 (Ae = Ca, Sr, Ba; X(II) = Mg, Zn; X(III) = Al, Ga; X(IV) = Si, Ge). For all systems we found a pronounced pseudo-gap in the density of states separating network X42- bonding from antibonding electronic states that coincides with the Fermi level for an electron count of 14 electrons per formula unit, the optimum value for stable BaAl4-type polar intermetallics. However, the synthesis and structural characterization (from X-ray single crystal and powder diffraction data) of the new compounds AeZn2-Al2+, AeZn2-deltaGa2+delta (Ae = Ca, Sr, Ba; delta = 0-0.2) and AeMg0.9Al3.1, AeMg1.7Ga2.3 (Ae = Sr, Ba) manifested that electron deficiency is rather frequent for BaAl4-type polar intermetallics. The site preference for different "X" elements in the ternary systems was quantified by calculating "coloring energies", which, for some systems, was strongly dependent on the size of the electropositive Ae component. The Ae2+ cations decisively influence the nearest neighbor distances in the encapsulating polyanionic networks X4(2-) and the structures of these networks are surprisingly flexible to the size of the Ae component without changing the overall bonding picture. A monoclinically distorted variant of the BaAl4 structure occurs when the cations become too small for matching the size of encapsulating X4(2-) cages. An even larger size mismatch leads to the formation of the EuIn4 structure type.