CONTRIBUTION TO STRUCTURAL STUDY OF SOLID WUSTITE AT HIGH-TEMPERATURE

The structure of wüstite Fe1-zO is studied by neutron diffraction on one polycrystalline sample under equilibrium conditions at high temperature. The mean isotrope temperature factor B is expressed as a sum of two parts, BTh and BSt, which vary linearly with a single parameter, respectively temperature and z. A classification is established for clusters ( m n) settled from m vacancies in octahedral sites and n FeIII ions in interstitial sites. Sixteen values have been experimentally determined for the vacancies to interstitials ratio ρ{variant} = (z + t) t = m n. A constant value of ρ{variant}, which is lower than 3, is observed. This result characterizes the short-range order. It eliminates several possibilities of clusters like those obeying the relation ρ{variant} = (1 + 3n) n. Other clusters, namely ( 16 6) or ( 40 14), might agree. The ( 8 3) and ( 9 4) clusters obtained from ( 4 1) clusters joined by an edge would be the more likely. An analysis of diffuse scattering eliminates the hypothesis of large domains with inverse spinel structure. The structural differences between the three varieties W1, W2 and W3 would not be found in a structural change of clusters. © 1979.