SYNTHESIS AND PHYSICAL PROPRETIES OF

Co2+Fe23+(P2O7)2 and Mg2+Fe23+(P2O7)2

A. Oulmekki1, M. Ijjaali1*, El. El Ghadraoui1, B. Malaman2, N. Tijani3

1 Laboratoire de Chimie Minérale, Faculté des Sciences et Techniques Fès Saiss, B.P. 2202 FES MAROC

2 Laboratoire de Chimie du Solide Minéral Université Henri Poincaré Nancy I, B.P. 239,

54506 Vandoeuvre les NancyCedex,France

3 Faculté des Sciences de Méknes, MAROC

* Corresponding author. E-mail : ijjaali@yahoo.com

Received : 20 April 2001; revised version accepted 26 September 2001

Abstract

Investigations made by powder X-ray diffraction have shown that two new phosphates : Mg2+Fe23+(P2O7)2 and Co2+Fe23+(P2O7)2 are isostructural to Fe2+Fe23+(P2O7)2. They crystallize in the orthorhombic Fe2+Fe23+(P2O7)2-type structure (space group Pnma). The magnetic susceptibility measurement and Mössbauer effect have been reported.

An unusual feature of this presence of this presence of (Fe3O12)16- trimers, Where trigonal prismatic Fe2+ is linked to 2 opposite octahedral Fe3+ through shared faces; these isolated trimers are connected by P2O7 groups. It clearly appears that Co2+ and Mg2+ occupy the trigonal prismatic Fe2+ site, whereas the octahedral site is occupied by Fe3+. The room temperature Mössbauer spectrum is characteristic of the Fe3+ valence state.

Co2+Fe23+(P2O7)2 and Mg2+Fe23+(P2O7)2 exhibit an antiferromagnetic-paramagnetic transition respectively at TN = 8± 2 K and TN = 14± 2 K.

Keywords : Iron-cobalt phosphate; Iron magnesium phosphate; Magnetic properties.

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