Zr-doped ceria nanotubes (Zr x Ce 1-x O 2 ) were obtained in a high yield from a hydrothermal reaction in an aqueous solution of NaOH with Ce(NO 3 ) 3 • 6H 2 O and ZrO 2 powder in a small proportion. The morphology and crystalline structure were characterized with X-ray diffraction, a scanning electron microscope, and a transmission electron microscope. Mechanisms for the growth of Zr-doped ceria nanotubes are proposed based on the Kirkendall effect; the formation of the tubular structure is strongly dependent on the precursor. This is the first report of a direct synthesis of cerium-oxide nanotubes in high yield. The surface area of the nanotubes is 76 m 2 /g and their average pore size is ∼52.2 nm. Catalytic measurements show that the nanotubes as synthesized are active for an oxygen-storage capacity and for ethanol reforming.

The crystal structure is related to Proudite-Felbertalite homologous series and is made up of layered units ∞ 2 M 16 Se 23 ½ � derived from the octahedrally coordinated MSe 6 with stepped layers of 16 octahedra overlapped by 8 octahedra units, and 1D ribbons ∞ 1 M 12 Se 14 ½ � with metal centers coordinated by 3 or 5 Se 2À anions. Structural anisotropy leads to their layered shape and strong preferred orientation. The quinary selenide Sn 3.84 Pb 6.16 Sb 5.68 Bi 12.32 Se 37 exhibits n-type semiconducting behavior and thermoelectric properties with an optimized thermoelectric figure of merit (zT) reaching ~0.09 at 440 K. Density functional theory (DFT) calculation on a chargebalanced model with a triple supercell indicates its indirect band gap.

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The title compounds are synthesized from the elements (1023 K, 16 h).

7 . -The new compounds Na10Sn31(HPO4)6(P2O7)6(PO4)12 (I) and K2SnP2O7 (II) are synthesized by solid state reactions of mixtures of M2HPO4 (M: Na, K), Sn, SnO2, and P2O5 (silica tube, slow heating to 600°C, 48 h) and structurally characterized by single crystal XRD. Compound (I) crystallizes in the hexagonal space group P62c with Z = 1 and (II) in the monoclinic space group P2 1 /n with Z = 4. The structure of (I) contains SnO 3 and SnO 4 polyhedra sharing corners with [HPO4] 2-, [PO4] 3-, and [P2O7] 4groups forming tunnels of six rings filled with Na + cations, which are connected via O-Sn-O bridges resulting in a three-dimensional open framework. The crystal structure of (II) contains SnO4 seesaw polyhedra sharing vertices with diphosphate groups to form a three-dimensional [SnP 2 O 7 ] 2framework with a tunnel structure of 10-and 12-membered rings.