Orthorhombic WO3Formed via a Ti-Stabilized WO3·13H2O Phase

✍ Scribed by B Pecquenard; H Lecacheux; J Livage; C Julien

• Book ID: 102604211
• Publisher: Elsevier Science
• Year: 1998
• Tongue: English
• Weight: 331 KB
• Volume: 135
• Category: Article
• ISSN: 0022-4596
• DOI: 10.1006/jssc.1997.7618

✦ Synopsis

Stable solutions of WO 3 precursors have been prepared via the dissolution of tungstic acid, H 2 WO 4 , in hydrogen peroxide. A crystalline peroxopolytungstic acid WO 3 • H 2 O 2 • nH 2 O (n+0.1) is obtained upon drying. Peroxo groups decompose at 200°°C, giving an amorphous tungsten oxide that crystallizes into the stable monoclinic WO 3 around 400°°C. Completely different results are obtained when Ti(OPr i ) 4 is added to the precursor solution. The orthorhombic phase WO 3 • 1 3 H 2 O is first obtained. As is well known, this hydrated oxide leads to h-WO 3 and m-WO 3 upon heating. However, in the presence of Ti IV , a new metastable orthorhombic tungsten oxide is formed around 400°°C. It then transforms irreversibly upon further heating into the stable monoclinic WO 3 . The presence of Ti IV seems to stabilize this new orthorhombic phase.