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Equilibrium Cation Distribution in NiAl 2 O 4 , CuAl 2 O 4 , and ZnAl 2 O 4 Spinels
Author(s) -
COOLEY RICHARD F.,
REED JAMES S.
Publication year - 1972
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/j.1151-2916.1972.tb11320.x
Subject(s) - nial , stoichiometry , crystallography , aluminate , chemistry , materials science , thermodynamics , analytical chemistry (journal) , intermetallic , metallurgy , physics , alloy , cement , chromatography
Stoichiometric NiAl 2 O 4 , CuAl 2 O 4 , and ZnAl 2 O 4 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 NiAl 2 O 4 , x increased from 0.07 at 595° to 0.26 at 1391°C; in CuAl 2 O 4 , x decreased from 0.68 at 613° to 0.64 at 1195°C; and in ZnAl 2 O 4 , 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.