Single crystals of new orthophosphates AMg 2 Fe(PO 4 ) 3 (A = Sr or Ba) have been synthesized by solid-state reaction. From single crystal X-ray diffraction data, their corresponding crystal structures were solved in the orthorhombic system, with the Imma space group and unit cell parameters a = 10.3998 (2) Å, b = 13.2000 (2) Å, c = 6.5364 (1) Å for the strontium compound and a = 10.4996 (2) Å, b = 13.2696 (1) Å, c = 6.6330 (2) Å for the barium compound. Both phosphates crystallize with the α-CrPO 4 structure type. The crystal structure of both orthophosphates is composed of MgO 6 octahedra, FeO 6 octahedra, and PO 4 tetrahedra. The sharing of vertices between those polyhedra leads to a three-dimensional network defining hexagonal tunnels that are occupied by Sr 2+ or Ba 2+ cations.
Saleck et al. (Thu,) studied this question.