Computational study of substitution of Al by Fe3+ in the AlPO4-5 framework

In this paper we deal with the incorporation of Fe3+ into the framework of AlPO4-5. Calculations were performed using energy minimization techniques. Two cases were taken into account: one Fe3+ ion in the full unit cell (Al3/Fe3+ = 23/1) and one Fe3+ in the asymmetric unit cell (Al3+/Fe3+ = 5/1). I n both cases the energy difference between the configurations studied is sm all, which demonstrates an hexagonal pseudo-symmetry. The substitution prod uces distortion around the Fe atom and strong variation in cell parameters; this variation is highly dependent on the substituted site. The results sh ow that Fe3+ in tetrahedral sites destabilizes, but does not disrupt, the s tructure. (C) 1999 Elsevier Science B.V. All rights reserved.