A novel phosphate with CoII square planar coordination, BaCo0.5Fe(PO4)2: structural and magnetic features

Abstract

A novel phosphate containing barium, cobalt, and iron was synthesized in single-crystal and polycrystalline forms. Single crystal-based X-ray measurements revealed that it crystallizes in the monoclinic system with the P2₁/c space group. The structure is made up of linkages between FeO₆ octahedra, CoO₄ square planar units, CoO₅ square pyramidal units, and PO₄ tetrahedra through edges and/or vertices. The interconnection of these polyhedra leads to a three-dimensional framework with tunnels along the a-axis where the Ba²⁺ cations are located. The polycrystalline form was prepared via the sol–gel method and its XRD pattern was refined by the Le Bail method. Morphological and elemental mapping analyses of this phosphate were performed by scanning electron microscopy. In addition, infrared and Raman spectroscopy provided more insights into chemical bonding. The magnetic behavior was antiferromagnetic below T_N ∼ 20 K. Optical measurements revealed a direct bandgap with an energy E_g of 2.83 eV.