Crystal structure, phase transitions, and thermodynamic properties of magnesium metavanadate (MgV₂O₆)

As a promising anode material for magnesium ion rechargeable batteries, magnesium metavanadate (MgV2O6) has attracted considerable research interest in recent years. A MgV2O6 sample was synthesized via a facile solid-state reaction by multistep-firing stoichiometric mixtures of MgO and V2O5 powder under an air atmosphere. The solid-state phase transition from alpha-MgV2O6 to beta-MgV2O6 occurred at 841 K and the enthalpy change was 4.37 +/- 0.04 kJ/mol. The endothermic effect at 1014 K and the enthalpy change was 26.54 +/- 0.26 kJ/mol, which is related to the incongruent melting of beta-MgV2O6. In situ XRD was performed to investigate phase transition of the as-prepared MgV2O6 at high temperatures. The cell parameters obtained by Rietveld refinement indicated that it crystallizes in a monoclinic system with the C2/m space group, and the lattice parameters of a = 9.280 & Aring;, b = 3.501 & Aring;, c = 6.731 & Aring;, beta = 111.76 degrees. The solid-state phase transition from alpha-MgV2O6 to beta-MgV2O6 was further studied by thermal kinetics, indicating that this process is controlled first by a fibril-like mechanism and then by a spherulitic-type mechanism with an increasing heating rate. Additionally, the enthalpy change of MgV2O6 at high temperatures was measured utilizing the drop calorimetry, heat capacity was calculated and given as: Cp = 208.3 + 0.03583T-4809000T(-2) (298 - 923 K) (J mol(-1) K-1), the high-temperature heat capacity can be used to calculate Gibbs free energy of MgV2O6 at high temperatures. (c) 2022 Chongqing University. Publishing services provided by Elsevier B.V. on behalf of KeAi Communications Co. Ltd.