Thermodynamic, lattice dynamical, and elastic properties of iron-vanadium oxides from experiments and first principles

The thermodynamic, lattice dynamical, and elastic properties of iron-vanadium oxides are studied from experiments and first-principles calculations. The high-temperature heat capacities of FeVO4, Fe2V4O13, FeV2O4, and FeV3O8 are accurately measured using a three-dimensional (3D) sensor. The phase diagram of Fe-V-O system at 873 K is reasonably predicted combining the calculated enthalpy of formation and entropy. The phonon dispersions of FeVO4 and Fe2V4O13 indicate that they are dynamically stable. The high-frequency vibrations are dominated only by V and O atoms mainly due to the stronger V-O bonding. All Raman and infrared (IR) frequencies at zone-center are assigned unambiguously and different types of vibration are established. The physical properties such as elastic constant, bulk modulus, shear modulus, Young's modulus, Poisson's ratio, Debye temperature, elastic wave velocity, and minimum thermal conductivity of FeVO4 and Fe2V4O13 are calculated.