Phase transitions, lattice dynamics, thermal transport, and thermodynamic properties of Mg₂V₂O₇ from experiments and first-principle calculations

Mg₂V₂O₇ is the most promising candidate for low-temperature co-fired ceramic (LTCC) multilayer devices. Selecting the appropriate precursors strongly requires reliable thermodynamic properties to be defined accurately. In this study, the structural parameters of the Mg₂V₂O₇ at ambient temperature indicate that it is crystallized in space group of P2₁/c. Notably, Mg₂V₂O₇ has low lattice thermal conductivity (k_L) of 4.77, 5.12, and 4.52 W/mK, along the a, b, and c axes, respectively, which originates from the large phonon scattering rate and low phonon group velocity. The α-Mg₂V₂O₇↔β-Mg₂V₂O₇ and β-Mg₂V₂O₇↔γ-Mg₂V₂O₇ polymorphic transitions occur at 743 ℃ and 908 ℃ with enthalpy change of 1.82±0.04 kJ/mol and 1.51±0.04 kJ/mol, respectively. The endothermic effect at 1083 ℃ with an enthalpy change of 26.54±0.26 kJ/mol is related to the congruent melting of γ-Mg₂V₂O₇. In addition, the molar heat capacity of Mg₂V₂O₇ was measured utilizing drop calorimetry at high temperatures. The measured thermodynamic properties were then applied to select precursors for preparing Mg₂V₂O₇ via a solid-state reaction, indicating that the V₂O₅ and Mg(OH)₂ precursors are strongly recommended due to their thermodynamic superiority.