In situ XAFS study of phase transitions and hydrogen intercalation in WO3-MoO3 system

The WO3-MoO3 system has several reconstructive and displacive phase transitions which can be induced by temperature and/or by change of stoichiometry or valence state of metal ions under hydrogen intercalation. We have studied in situ the local electronic and structural changes arising in WO3-MoO3 system with hydrogen intercalation and temperature. In situ XAFS measurements at the Mo K and W L3 edges in HyMoxW1-xO3 compounds, performed at different hydrogen intercalation level and temperatures (from RT to 500 C), allowed us to determine the rearrangement in the first and second coordination shells of Mo and W cations during phase transitions. It was found that hydrogen insertion leads, depending on W/Mo ratio, to the appearance of localized (mixed valence) or delocalized electronic states with different Mo and W surrounding. ((orig.))