Effect of defects on the elastic properties of Wustite.

Wustite (FexO) has been studied under static high pressure in the composition range x = 0.95-0.99. Fe0.99O is substantially less compressible than FexO 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 FexO 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.