Defect and metastable structures were studied by using a Born-like description of the ionic lattice, and by using a shell model to represent the polarization of ions. It was found that the calculated normal spinel structure of the present material had a lower energy than that of other metastable structures. An amorphous form of the present material was simulated, and it was found that the volume of the amorphous state was larger (and the Young’s modulus was smaller) than those of the normal spinel. This agreed with experimental observations. In agreement with other studies of spinel materials, the most energetically accessible disorder mode was via the exchange of cations. The energy which was necessary for this disordering reaction was far lower than that for either Frenkel or Schottky reactions. Phases which were intermediate between the normal and amorphous forms were also considered.

S.P.Chen, M.Yan, J.D.Gale, R.W.Grimes, R.Devanathan, K.E.Sickafus, N.Yu, M.Nastasi: Philosophical Magazine Letters, 1996, 73[2], 51-62