Discovery of the High-Pressure Phase of Ba3W2O9 and Determination of Its Crystal Structure

Daisuke Urushihara; Toru Asaka; Koichiro Fukuda; Hiroya Sakurai

doi:10.1021/acs.inorgchem.7b01755

Discovery of the High-Pressure Phase of Ba₃W₂O₉ and Determination of Its Crystal Structure

Inorg Chem. 2017 Nov 6;56(21):13007-13013. doi: 10.1021/acs.inorgchem.7b01755. Epub 2017 Oct 11.

Authors

Daisuke Urushihara, Toru Asaka, Koichiro Fukuda, Hiroya Sakurai¹

Affiliation

¹ National Institute for Materials Science , 1-1 Namiki, Tsukuba 305-0044, Japan.

PMID: 29019406
DOI: 10.1021/acs.inorgchem.7b01755

Abstract

A new polymorphism of Ba₃W₂O₉ is discovered with the use of a high-pressure synthesis technique and its crystal structure is determined by single-crystal X-ray diffraction and transmission electron microscopy. The crystal structure was isostructural with that of Ba₃Re₂O₉, having a hexagonal unit cell of R3̅m symmetry with a = 0.574060(10) nm and c = 2.08256(4) nm. The high-pressure (HP) phase is obtained from a transformation of an ambient-pressure (AP) phase of the compound, which has the Cs₃Tl₂Cl₉-type structure. The most notable change in the transformation is the connection of WO₆ octahedra. The HP phase has corner-sharing octahedra, which form a bilayer structure, while the AP phase has face-sharing octahedra of isolated [W₂O₉] dimers. This type of the structural phase transition is unreported although it is possibly that a sequence of high-pressure structural transformations occurs for similar chemical compositions. The HP phase has W ions in WO₆ octahedra with an unusual off-center displacement; although the displacement is slightly relaxed compared with that of the AP phase. The off-center displacement suggests strong hybridization between the W 5d orbitals and O 2p orbitals.