Synthesis, Characterization and Structural Study of the Novel Phosphate Ag0.4Zn2.8Fe4(PO4)6

Abstract

Ag 0.4 Zn 2.8 Fe 4 (PO 4 ) 6 was prepared by classical solid-state method and investigated by means of single-crystal X-ray diffraction (XRD). The purity of the sample was checked by energy dispersive X-ray spectroscopy (EDS). This new phase adopts the typical Howardevansite structure with the triclinic system, space group P -1 and unit cell parameters: a = 6.3551(1), b = 7.9271(1), c = 9.3232(2) Å, α = 105.022(1)°, β =108.085(1)°, and γ = 101.470(1)°. All atoms of the crystal structure occupy the general position 2i except Ag(1) + and Zn(1) 2+ cations which are on two centers of inversion at 1g(-1) and 1h(-1), respectively. This crystal net-framework is made up of folded chains of polyhedral with shared edges based on [Fe(1) 2 O 10 ] and [Fe(2) 2 O 10 ] dimers intercalated by Zn(2)O 5 unit. Adjacent chains are interconnected by a regular PO 43-tetrahedra and ordered in stacked layers perpendicular to [010]. Such an arrangement gives rise to tunnels parallel to [100], that host Ag(1) + and Zn(1) 2+ cations. The stability and accuracy of the suggested structural model have been approved by combinatorial investigations of charge distribution (CD) and bond valence sum (BVS).