High‐pressure synthesis and crystal structure of the strontium tungstate Sr 3 W 2 O 9

The strontium tungstate compound Sr 3 W 2 O 9 was prepared by a high‐pressure synthesis technique. The crystal structure was determined by single‐crystal X‐ray diffraction and transmission electron microscopy. The structure was found to be a hettotype structure of the high‐pressure phase of Ba 3 W 2 O 9 , which has corner‐sharing octahedra with a trigonal symmetry. Sr 3 W 2 O 9 has a monoclinic unit cell of C 2/ c symmetry. One characteristic of the structure is the breaking of the threefold rotation symmetry existing in the high‐pressure phase of Ba 3 W 2 O 9 . The substitution of Sr at the Ba site results in a significant shortening of the interlayer distances of the [ A O 3 ] layers ( A = Ba, Sr) and causes a distortion in the crystal structure. In Sr 3 W 2 O 9 , there is an off‐centre displacement of W 6+ ions in the WO 6 octahedra. Such a displacement is also observed in the high‐pressure phase of Ba 3 W 2 O 9 .