首页|Crystal structure,phase transitions,and thermodynamic properties of magnesium metavanadate(MgV2O6)
Crystal structure,phase transitions,and thermodynamic properties of magnesium metavanadate(MgV2O6)
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As a promising anode material for magnesium ion rechargeable batteries,magnesium metavanadate(MgV2O6)has attracted considerable re-search 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 α-MgV2O6 to β-MgV2O6 occurred at 841 K and the en-thalpy change was(4.37±0.04)kJ·mol-1.The endothermic effect at 1014 K and the enthalpy change was(26.54±0.26)kJ·mol-1,which is related to the incongruent melting of β3-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=0.9280 nm,b=0.3501 nm,c=0.6731 nm,β=111.76°.The solid-state phase transition from α-MgV2O6 to β-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 meas-ured 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.
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