Structural characterization and colour of MgxCu3-xV2O8 (0 ≤ x ≤ 3) and MgyCu2-yV2O7 (0 ≤ y ≤ 2) compositions

In this study, MgxCu3-xV2O8 (0 ≤ x ≤ 3) and MgyCu2-yV2O7 (0 ≤ y ≤ 2) compositions were synthesized by the chemical coprecipitation method and characterized by X-ray diffraction, UV-vis-NIR spectroscopy and CIE L* a* b* parameters measurements. Melting points of compounds Cu3V2O8 and Cu2V2O7 are 780°C and 790°C, respectively. The addition of small amounts of Mg (II), MgxCu3-xV2O8 (x < 1.0) and MgyCu2-yV2O7 (y < 0.5) fused compositions, was not sufficient to stabilize structures at 800°C. For the Mg2CuV2O8 (x = 2.0) composition fired at 800°C, Mg (II) incorporated into the monoclinic Cu3V2O8 structure stabilizes this crystalline phase. At 1000°C, orthorhombic Mg3V2O8 structure from this composition was obtained. Solid solutions with orthorhombic symmetry were detected from the prepared compositions fired at 1000°C when 1.0 ≤ x ≤ 3.0. The difference of coloration of Cu, Mg vanadates might be explained by the presence of a strong charge transfer band in visible spectra.