Defect structure of pseudo phases of wüstite

Surface versus Bulk Defect-Related Properties of the Wüstite Phase (FeO) in Gas/Solid Equilibrium

“…This work determined the isothermal WF changes of the iron-oxygen system across the stability range of the FeO phase in the temperature range 948–1223 K. The resulting slope of the WF changes as a function of oxygen activity, which is proportional to the parameter 1/ m Φ , is reflective of the defect disorder of the surface layer of the wüstite phase. Comparison of this quantity with a similar bulk-related quantity, 1/ m y , which is related to mass changes determined by thermogravimetry, allows drawing the following conclusions: The isothermal effect of p (O 2 ) on the bulk defect-related parameter 1/ m y (determined by thermogravimetry) is consistent with the reported interactions between intrinsic defects in the FeO phase, leading to the formation of defect complexes and larger defect aggregates. ,− The effect of temperature on the parameter, 1/ m y , indicates that interactions between defects in the bulk change with decreasing of temperature. The slope of WF versus log p (O 2 ) linear dependence within the stability of the FeO phase (i) exhibits a constant value within the stability range of the FeO phase and (ii) is independent of the applied experimental procedure, confirming that the surface layer is in gas/solid equilibrium. The defect disorder of the FeO surface is different from that of the bulk phase …”

“…Vallet and Raccah 28 postulated that defect disorder of FeO may be considered in terms of three structural domains that have been recently confirmed by Worral and Coley. 29,30 Application of the Debye− Huckel theory of strong electrolytes indicated that the 4:1 cluster, with an ionization degree of −5, explains the properties of the FeO phase within the entire range of composition. 7 The complex picture of FeO defect disorder results in a range of conflicting reports.…”

The complex nonstoichiometry of wüstite Fe1-O: Review and comments

“…Finally, Worral and Coley declared that, in their study, transitions at 850 °C and 995 °C were observed « correspond[ing] exactly with the proposed pseudo-phase boundaries in quite good agreement with the phase diagram by Vallet and Carel». Because of the identity of coefficients m in the correlations concerning Wi and W'j for i=j, they attributed in a following review [22] three predominant clusters (7:2) type II to w1 and w'1, (12:4) type II to w2 and w'2 and (16:5) type I to w3 and w'3.…”

“…Labidi and Monty (see [135] p. 100-101) resumed the situation differently with the types 1 (face shared) aligned in <100> direction, 2 (edge shared) aligned in <110> direction, and 3 (corner shared) aligned in <111> direction. Worral and Coley (see [22] p. 24-26) classified the clusters in three types defined as either type 1 (corner shared as in magnetite), type 2 (edge shared sharing one octahedral vacancy), or type 3 (edge shared sharing two octahedral vacancies).…”

“…Goodenough [1], Kofstad [2], Vallet [3], Burgmann [4], Gokcen [5], Men' et al [6], Spencer, Kubaschewski [7], Bauer, Pianelli [8], Sorensen [9], Hazen, Jeanloz [10], Gleitzer, Goodenough [11], Gokcen [12], Lykasov et al [13], Mrowec, Podgorecka [14], Long, Grandjean [15], Sundman [16], Wriedt [17], Collongues [18], Gleitzer [19], Smyth [20], Desré, Hodaj [21], Worral, Coley [22].…”