Abstract
Stoichiometric NiAl2O4, CuAl2O4, and ZnAl2O4 spinels were prepared and equilibrated at temperatures from 600° to 1400°C. The parameters u and x, denoting the oxygen position and fraction of divalent cations on tetrahedral sites, respectively, were determined from a detailed X‐ray diffraction analysis. In NiAl2O4, x increased from 0.07 at 595° to 0.26 at 1391°C; in CuAl2O4, x decreased from 0.68 at 613° to 0.64 at 1195°C; and in ZnAl2O4, x decreased from 0.96 at 905° to 0.94 at 1197°C. The form of the temperature dependence of x could not be described using theoretically based equations advanced in the literature. A more general equation which allows for a non‐distributional contribution to the configurational entropy was derived and observed to properly describe the temperature dependence; the results indicate that short‐range order is of definite significance in these intermediate aluminate spinels.
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