Synthesis, structure and properties of compounds stabilized in wolframite structure: (AA')(BB')O 8 ; A = Zn 2+ , Mg 2+ , Co 2+ , Ni 2+ , Cu 2+ , A

Abstract

A series of compounds with the formula (AA')(BB')O8, stabilized in the monoclinic wolframite structure, were prepared and characterized. Rietveld refinement confirmed that the structures belong to the wolframite family of compounds. The XPS analysis established the different oxidation states of the ions in the compounds. The substitution of transition elements at the Zn site enabled the preparation of new colored compounds. The optical absorption behavior (UV-Visible spectroscopy) was understood based on metal-to-metal charge transfer (MMCT) and allowed d-d transitions. The NIR reflectivity studies suggested that the synthesized parent white and colored compounds exhibit good NIR reflectivity values, comparable to TiO2. Magnetic studies indicated antiferromagnetic interactions. The temperature-dependent dielectric studies exhibited high dielectric constant values with low dielectric losses at low frequencies. The DFT calculations were supportive of the experimental findings of the band gap and provided pointers about the participating orbitals at and near the Fermi level. The compound, CoFeNbWO8, was found to be a useful electrocatalyst for the oxidation of water (OER).