Local and electronic mechanisms of the 7-fold coordination transition in “metallic” WO3

Our goal is to probe the densification transition, local structure mechanisms, and electronic evolution of both amorphous WO3 and crystalline 7-coordinated “metallic” WO3, using XAS under high-pressure conditions. Amorphous (a) and crystalline (c) WO3 present distinct electronic properties, which are mainly concerned to the formation of localized electronic states, contingent upon the crystallinity degree. The significance of this fact for industrial applications is profound, as the level of crystallinity enables precise adjustment of their properties. The crystalline WO3 has several polymorphic phases reported under pressure; however, none is known on possible amorphous-amorphous transitions in a-WO3. Densification accompanied by an increase in CN from 6 to 7 is anticipated to occur in a-WO3, since it was described for its crystalline counterpart. The proposed experiment will shed light on the average coordination numbers and packing efficiencies in compressed WO3.