A double pyrovanadate CaMgV
2O
7 sample was synthesized via a facile solid-state route under an air atmosphere. The nonequilibrium formation pathways of the CaMgV
2O
7 were investigated via powder X-ray diffraction. A multistep reactions path (metavanadates–pyrovanadates–double pyrovanadate CaMgV
2O
7) was proposed to describe the formation of the CaMgV
2O
7 considering the thermodynamic and kinetic factors. The cell unit parameters of the CaMgV
2O
7 sample indicated the crystallization according to a monoclinic system with space group
P12
/c1(14), and the lattice parameters of
a = 6.756 Å,
b = 14.495 Å,
c = 11.253 Å,
β = 99.12, and
V = 108.806 Å
3. X-ray photoelectron spectroscopy also confirmed the +5 oxidation state vanadium in CaMgV
2O
7. The endothermic effects at 1033 and 1143 K were related to the incongruent melting and liquidus temperatures of CaMgV
2O
7, respectively. The comprehensive thermodynamic properties of CaMgV
2O
7 were established in both low- and high-temperature regions, utilizing a physical property measurement system and multi-high-temperature calorimetry (96 lines). The heat capacity (200 J mol K
−1) and entropy (198 J mol K
−1) at 298.15 K were computed based on the low-temperature heat capacity values, and the enthalpy of formation at 298.15 K was also estimated. The fitted high-temperature capacity can be used to obtain the changes in the enthalpy, entropy, and Gibbs free energy. This study is part of building a reliable thermodynamic database of the CaO–MgO–V
2O
5 system.
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