Na7Nb15W13O80 – A new type of tunnel structure studied by X-ray diffraction and HREM techniques

Abstract

Abstract. orthorhombic, Pmab, a= 21.962 (2), b = 17.763 (2), c= 3.9165 (3),/k, V---1527.9 (3) A 3, Z= 1, Din= 5.61 (1), Dx= 5.664 (1) g cm -3, 2(Mo Ka) = 0.7107 ,/~, /t(Mo Ka) = 241 cm -l, F(000) = 2292.7, T= 293 K, R = 0.058 for 936 independent reflexions. The structure is built up of pentagonal columns connected to each other directly and via a string of MO 6 octahedra, running parallel to the c axis. Large tunnels with an S-shaped cross section are formed, in which the Na atoms are statistically distributed. Four of the five heavy-atom sites are randomly occupied by Nb and W; the fifth entirely by Nb. X-ray and electron diffraction experiments indicate that the K and Ag analogues are isostructural. HREM images of the K compound confirm the structure.

Materials Discovery by Flux Crystal Growth: Quaternary and Higher Order Oxides

“…Neither the aluminum nor the titanium were incorporated into the major product, however, small colorless octahedra of LiAl 5 O 8 and (Al x Sc 1− x ) 2 TiO 5 were isolated in minor yield. Na 7 Nb 15 W 13 O 80 74 crystallized in a melt of NaCl at 897 °C, followed by slow cooling at 1 °C per hour to generate small platelets. The spinel compound Li 0.65 Co 1.29 Mn 1.06 O 4 75 was prepared from a 1:1 ratio of CoCl 2 and MnCl 2 with a sixty fold excess of LiCl serving as a flux.…”

A Detailed Structural Analysis of CdxNb6(O,F)16

“…However, it cannot be excluded that the holes contain further light cations that do not scatter enough to be detected by HAADF‐STEM besides niobium. These arrangements show some similarity to the Na‐filled sites present in Na 7 Nb 15 W 13 O 80 . The contrast at a different site can be interpreted as a six‐membered ring (marked B in Figure d) that hosts further metal atoms (bright spot encircled in Figure c).…”

Quaternary Lead–Niobium–Tungsten Oxides Based on the Tetragonal Tungsten Bronze Structure

“…Region A cannot correspond to the pseudo-TTB PC phase m-TTB, since the high lead content precludes the formation of su$cient PCs. (23), but studies of Na}Nb}W}O phases did report weak doubled c periodicities in some SAED patterns (25,26), and odd-order Laue layer superstructures have been observed and characterized in studies of some TTB bronzes (34, 43}45) and TTB ferroelectric phases (e.g., 46, 47). Of particular relevance to Pb}Nb}W}O phases is the observation of large supercells on non-zero Laue layers in the related ternary phases of lead-TTB (34) and PbNb O (35}37).…”