Synthesis, single crystal structure, optical and magnetic properties of a new rubidium nickel iron phosphate RbNiFe(PO4)2

New RbNiFe(PO4)2 phosphate, both in single and powder forms, was synthesized by flux method and solid state reaction. It is characterized by crystal-X-ray diffraction, HRTEM, IR and Raman spectroscopy and UV-diffuse reflectance. Its crystal structure adopts the monoclinic P21/c space group with the cell parameters: a= 5.134 (4) & ANGS;, b= 14.547(2) & ANGS;, c= 9.230(2) & ANGS;; & beta;=103.76(3) degrees and Z= 4. The RbNiFe(PO4)2 framework has a threedimensional structure, consisting of chains of edge-sharing NiO6, isolated FeO5 and PO4 tetrahedra sharing vertices and edge to form large tunnels along the [100] direction, where Rb + cations are placed. The IR and Raman data are in good agreement with the number of PO4 groups determined in crystal structure. Diffuse reflectance spectroscopy leads to a gap energy of 3.15 eV. It also proved the presence of isolated Fe3+ ions from low energy due to the inter-electronic transition from oxygen to Ni (II) and the non-existence of d-d transition related to iron. The colorimetric properties of the compound result mainly from d-d visible transitions related to the Ni2+ cation in octahedral coordination. The magnetic study revealed that below the temperature of TN =21K an antiferromagnetic character appears with a Curie-Weiss constant of Ө =-97 K.

Automated summary

The new RbNiFe(PO4)2 phosphate was synthesized in single and powder forms using the flux method and solid state reaction. Characterization using various techniques revealed its crystal structure, which has a three-dimensional framework with large tunnels formed by chains of edge-sharing NiO6, isolated FeO5, and PO4 tetrahedra. The compound also exhibited a gap energy of 3.15 eV and d-d visible transitions related to the Ni2+ cation in octahedral coordination. Magnetic studies showed an antiferromagnetic character below a temperature of 21K.