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 (kL) 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°C and 908°C with enthalpy change of 1.82±0.04 kJ/mol and 1.51±0.04 kJ/mol, respectively. The endothermic effect at 1083°C 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.