ORTHORHOMBIC WO3 FORMED VIA A TI-STABILIZED WO3-CENTER-DOT-1 3H(2)O PHASE/

Stable solutions of WO3 precursors have been prepared via the dissolut ion of tungstic acid, H2WO4, in hydrogen peroxide, A crystalline perox opolytungstic acid WO3 . H2O2 . nH(2)O (n approximate to 0.1) is obtai ned upon drying, Peroxo groups decompose at 200 degrees C, giving an a morphous tungsten oxide that crystallizes into the stable monoclinic W O3 around 400 degrees C. Completely different results are obtained whe n Ti(OPri)(4) is added to the precursor solution, The orthorhombic pha se WO3 . 1/3H(2)O is first obtained, As is well known, this hydrated o xide leads to h-WO3 and m-WO3 upon heating, However, in the presence o f Ti-IV, a new metastable orthorhombic tungsten oxide is formed around 400 degrees C. It then transforms irreversibly upon further heating i nto the stable monoclinic WO3. The presence of Ti-IV seems to stabiliz e this new orthorhombic phase, (C) 1998 academic Press.