Exploration of Metal‐Metal Charge Transfer (MMCT) and its Effect in Generating New Colored Compounds in Mixed Metal Oxides

Abstract

AbstractCompounds belonging to the palmierite structure, (Zn3−xMx)A2O8 (M=Co, Ni, Cu and A=V, P) have been prepared employing solid state methods. The transition metal substituted compounds of Zn3V2O8 exhibits colors that are unique varying from mint green to forest green for Co2+ ions. The observed colors were understood based on the allowed d‐d transitions and metal to metal charge transfer (MMCT) transitions. The MMCT transitions involve partially filled d‐orbitals of Co2+ (3d7), Ni2+ (3d8), and Cu2+ (3d9) ions and the V5+ ions (3d0). The spinel compounds, Zn2−xCoxMO4 (M=Ti, Sn) were also prepared to understand the MMCT transitions in the compounds. Band structure calculations were carried out to understand the participating orbitals near the Fermi level and the band gap. The calculations support the idea that the substitution of transition elements in the palmierite structure reduces the overall band gap from 3.18 eV for Zn3V2O8 to 2.61 eV Zn2.5Co0.5V2O8 compound. This indicates the substitution of transition elements provide a tool towards band gap engineering.