A novel phosphate, K4NiFe3(PO4)5: Synthesis, crystal structure and magnetic properties

The design of phosphate materials with promising structures has attracted huge attention for various promising applications such as energy storage and catalysis. One of the major challenges facing numerous research teams, is the design and the understanding of the structure-properties relationship of new materials. The title phosphate, K4NiFe3(PO4)5, is synthesized in single crystal and polycrystalline forms. This phosphate crystallizes in a tetragonal symmetry, space group P 4¯ 21c, with a ​= ​9.6881(2) Å and c ​= ​9.4307(4) Å. Its crystal framework is constructed from the corner-sharing between PO4 tetrahedra and (Fe/Ni)O5 trigonal bipyramids leading to a three-dimensional framework delimiting elliptical-shaped tunnels running along [001] direction, where the K+ cations are located. The magnetic investigation shows the presence of ferrimagnetic ordering below Tc ​= ​17.8 ​K in addition to spin glass state below the spin-freezing temperature of Tf ​= ​7.8 ​K.