Effect of defects on the elastic properties of wustite

Wustite (Fe(x)O) has been studied under static high pressure in the composition range x = 0.95-0.99. Fe(0.99)O is substantially less compressible than Fe(x)O with x < 0.98. Such observations provide the only direct evidence of a significant effect of defect concentration on the elastic properties and support the results of crystal-field modeling for ideal stoichiometric wustite. The bulk moduli of Fe(x)O show a discontinuous variation at compositions that are within the predicted range for the defect clusters to form, a behavior that may be caused by an order-disorder transition of the defect structure. PACS numbers: 62.20.Dc, 46.25.-y, 61.72.Ji, 91.60.-x.