Superstructure and Twinning in the Tetragonal Tungsten Bronze-Type Phase Nb7W10O47

✍ Scribed by Frank Krumeich; Michael Wörle; Altaf Hussain

• Publisher: Elsevier Science
• Year: 2000
• Tongue: English
• Weight: 297 KB
• Volume: 149
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1999.8575

✦ Synopsis

Needle-shaped crystals of Nb 7 W 10 O 47 , a member of the solid solution series Nb 8؊n W 9؉n O 47 with n ‫؍‬ 1, were prepared from the binary oxides with HgCl 2 added as a mineralizer. All investigated crystals were twinned. The data set was measured on a fourling, which consists of 73% of an individual twin domain. The orthorhombic structure (a ‫؍‬ 1225.7(2), b ‫؍‬ 3663.3(6), c ‫؍‬ 394.96(6) pm) was re5ned in the space group P2 1 2 1 2 (No. 18) to a 5nal R value of 5.11%. The composition of this crystal determined from X-ray data is Nb 6.7 W 10.3 O 47 . Nb 7 W 10 O 47 crystallizes isostructural to Nb 8 W 9 O 47 in a threefold superstructure of the tetragonal tungsten bronze type. All atomic positions are considerably shifted out of the planes ( 001) and ( 002), leading to alternating short (&175 pm) and long (&220 pm) metal}oxygen distances along the short crystallographic c axis. One octahedral site is exclusively occupied by W, the center of the pentagonal bipyramid preferentially by Nb.