Band 238, Heft 1-2

Singe crystals of four new A I M II [ReO 4 ] 3 perrhenates ( A I  = Na, M II  = Pb; A I  = Na, M II  = Sr, Ag, K) have been prepared from the respective A I [ReO 4 ] and M II [ReO 4 ] 2 perrhenates using melt and solution evaporation techniques. All new compounds belong to the hexagonal CdTh[MoO 4 ] 3 structure type, similar to previously known NaCa[ReO 4 ] 3 . We discuss the crystal chemical relationships within this structure type and suggest existence of some more representatives involving other tetrahedral anions.

Single crystals of three mixed-valent oxidotellurates(IV/VI) with general formula M 2 Te IV Te VI O 6 (H 2 O) x ( M  = Na, K, Rb) were grown under hydrothermal conditions at 210 °C from M 2 CO 3 , TeO 2 and Te(OH) 6 in a 4:1:1 molar ratio. Na 2 Te 2 O 6 ·11/8H 2 O (where Te IV Te VI is abbreviated as Te 2 ) crystallizes as a monoclinic eightfold superstructure with occupational modulation of the water molecules. The structure is built of diperiodic corrugated [Te 2 O 6 ] 2− networks interleaved by the Na atoms and H 2 O molecules. The hexagonal crystal structures of M 2 Te 2 O 4 (OH) 4 ( M  = K, Rb; x  = 2) with P 6 3 / mmc symmetry are made up of [Te 2 O 4 (OH) 4 ] 2− rods extending in the [001] direction. The rods are connected by the M atoms. The [Te IV O 2 (OH) 2 ] units are disordered about the threefold axis, resulting in pronounced three-dimensional diffuse scattering.

YNiIn and YCuIn form complete solid solutions YNiIn 1− x Al x and YCuIn 1− x Al x , which were characterized on the basis of X-ray powder diffraction. The ZrNiAl type crystal structures (space groups P 6 ‾ 2 m $P\overline{6}2m$ ) of YNiAl ( a =  0.70386(9), c  = 0.38327(4) nm, w R 2  = 0.0424), YNiIn 0.77 Al 0.23 ( a  = 0.73895(9), c  = 0.37707(4) nm, w R 2  = 0.0498) and YCuIn 0.63 Al 0.37 ( a  = 0.73404(7), c  = 0.39045(4) nm, w R 2  = 0.0314) were refined from the single crystal X-ray diffraction data. Exemplarily the electronic structure of YNiAl was studied, manifesting substantial Ni–Al bonding within the three-dimensional [NiAl] substructure. Comparison of YNiAl with isotypic YNiIn shows stronger Ni–Al bonding as compared to Ni–In. Magnetic susceptibility measurements of YNiIn 1− x Al x ( x  = 0.1, 0.2, 0.7 and 0.9), YNiIn and YNiAl in the temperature range 3–300 K indicated Pauli paramagnetic behaviour with molar magnetic susceptibility of about 0.15–0.22 × 10 −3  emu/mol.

Sodalites of the general type |Na 8 X 2 |[T 1 T 2 O 4 ] 6 with X = Cl − , Br − , I − have been synthesized for Al–Si, Ga–Si, Al–Ge and Ga–Ge as T 1 –T 2 frameworks. The structures were examined using in-house and synchrotron X-ray diffraction, Raman spectroscopy, force-field structure optimizations and DFT based ab-initio molecular dynamics (MD) computations. Calculated phonon density of states (PDOS) of the 12 compounds show only minor differences within a framework composition with a lowering of certain phonon energies with increasing anion size. Earlier published Debye and Einstein temperatures obtained with a Debye-Einstein-anharmonicity (DEA) model approach are confirmed using the determined low-temperature lattice parameters (18 K–293 K) and show no correlation with the respective PDOS. Small-box refinements against radial pair distribution functions (PDF) allowed the determination of anisotropic displacement ellipsoids (ADP) for Na + and O 2− , indicating a strong dependency of the ADP of Na + on the chemical composition. Significantly lower thermal displacements from MD calculations suggested an influence of structural displacements. For compounds with an aspherical ADP for sodium, structural models could be refined in which the sodium is located on two 8e or one 24i site (both partially occupied), and also temperature-dependent (100 K–300 K) for the compounds with Ga–Ge framework. 3D-plots of the bond-valence sums of Na + further validate the structural differences. These results imply that the local structure of halide-sodalites in many cases is not best described by the known average structure and may even not be cubic.

The xBa(Ti (1− y ) Zr y )O 3 –(1− x )PbTiO 3 ceramic samples with x  = 0.3, y  = 0.95; x  = 0.3, y  = 0.7; x  = 0.3, y  = 0.3; x  = 0.3, y  = 0.05; x  = 0.5, y  = 0.05 were synthesized by a solid state reaction technique. The XRD patterns of these samples have anisotropic broadening of diffraction peaks. The crystallographic data were analyzed by the Rietveld method. During the refinement process the Stephens’s approach was used. All the samples studied are solid solutions with the tetragonal perovskite structure. The degree of tetragonal distortion of these solid solutions decreases with an increase in the Zr content. The microstructure analysis showed that the broadening of the diffraction peaks on the XRD patterns is due to both strains and small crystallite sizes.

Thermoelectric M x Co 4 Sb 12 skutterudites are well-known to exhibit a reduced thermal conductivity thanks to the rattling effect of the M-filler at the large cages occurring in the framework, centered at the 2 a sites of the I m 3 ‾ $Im\overline{3}$ space group. A novel Eu-filled skutterudite has been synthesized under high-pressure conditions at 3.5 GPa in a piston-cylinder hydrostatic press. The structural refinement from high-angular resolution synchrotron X-ray diffraction (SXRD) patterns unveils an unusual position for Eu filler atoms. By difference Fourier synthesis they are found at 12 d sites, conforming statistically occupied octahedra within the mentioned cages around 2 a positions. The Debye temperature was estimated by averaging the isotropic displacements by the atomic masses, leading to θ D ${\theta }_{D}$ of 273(2) K. Oftedal plots concerning the y and z Sb fractional positions, the unit-cell parameter a and M filling fraction include the novel Eu specimen in the trend observed for other filled materials prepared under high-pressure, including rare-earths, alkali or alkali-earth elements, all accepted as rattlers in filled skutterudites. A total thermal conductivity ( κ ) of 0.82 W m −1  K −1 is measured at 773 K for Eu 0.02(1) Co 4 Sb 12 , below that of other filled skutterudites, which is promoted by the enhanced phonon scattering of Eu located at 12 d sites. FE-SEM images showed large, homogeneous grains, well compacted after the high-pressure synthesis.

The intermetallic barium compounds Ba T Mg 2 ( T  = Pd, Ag, Pt, Au) and BaAuCd 2 were synthesized by reactions of the elements in sealed tantalum ampoules in muffle furnaces. The five compounds crystallize with the orthorhombic MgCuAl 2 type structure, space group Cmcm , with small differences in chemical bonding between the magnesium and cadmium series. All samples were characterized through their Guinier powder diffraction patterns. The structures of BaPdMg 2 ( a  = 444.57(4), b  = 1174.67(10), c  = 827.58(7) pm, w R 2 = 0.0460, 475 F 2 values, 16 variables), BaAuMg 2 ( a  = 450.27(6), b  = 1183.94(16), c  = 838.76(11) pm, w R 2 = 0.0355, 473 F 2 values, 16 variables) and BaAuCd 2 ( a  = 463.31(5), b  = 1112.79(12), c  = 826.63(8) pm, w R 2 = 0.0453, 469 F 2 values, 16 variables) were refined from single crystal X-ray diffraction data. The large barium atoms push the [ T Mg 2 ] respectively [AuCd 2 ] substructures apart. This allows fast moisture attack and leads to fast hydrolyzes of the samples when they get in contact with water. The influence of the difference in electronegativity between magnesium and cadmium is reflected for the pair of compounds BaAuMg 2 and BaAuCd 2 . The magnesium compound shows the higher auridic character, while the cadmium compound shows a tendency towards a three-dimensional cadmium substructure.

A two-dimensional uranyl organic framework (UOF) UO 2 (L)(DMA) ( 1 ) (H 2 L = 2-aminoisophthalic acid, DMA = N, N-dimethylacetamide) has been solvothermally synthesized and characterized thoroughly by elemental analysis, infrared spectroscopy, single-crystal X-ray diffraction, solid fluorescence, powder X-ray diffraction, thermogravimetric analysis, and UV–visible spectroscopy. Furthermore, the degradation efficiencies of UOF 1 to organic dye methylene blue (MB) and rhodamine B (RhB) are 93.2 and 86.5% under irradiation of visible light which indicates that UOF 1 has remarkable photocatalytic activity. UOF 1 also displayed a certain selectivity for mixed dyes of MB & RhB.