From experiments and first principles
Development of advanced materials has been identified as one way of curbing the growing global energy crisis and environmental problems. Among these materials, vanadates exhibiting unique electrochemical and redox properties have attracted significant research attention. For instance, iron-vanadates have been extensively explored as potential photoelectrode materials for various applications, including solar, lithium-ion batteries, and catalysts for degradation of organic pollutants. However, the realization of high-performance iron-vanadates requires a thorough understanding of their thermodynamic and lattice dynamical properties, which is yet to be achieved due to the challenge of accurate measurement of the mechanical properties of such materials. This can be attributed to two main reasons, namely, difficulty in preparing single crystals with sufficient size and the complexity of the multi-component materials.
Many mechanical parameters of materials are derived from their elastic constants. Thus, theoretical calculations of the elastic properties are useful in understanding mechanical properties, phase transition and interatomic interactions of such materials. Equipped with this knowledge, a team of researchers at the University of Science and Technology Beijing, Dr. Wei Xie, Professor. Xianran Xing and Professor Zhanmin Cao recently studied thermodynamics, lattice dynamical and elastic properties of iron-vanadium oxides. The main aim of the study was to provide key material properties for vanadium-oxides desirable for various applications. Their research work is currently published in the research journal, Journal of the American Ceramic Society.
In their approach, the investigations were based on experiments and first-principles calculations. First, the authors accurately measured the high-temperature heat capacities of four different iron-vanadium oxides: FeVO4, Fe2V4O13, FeV2O4 and FeV3O8 using a three-dimensional sensor. Next, the enthalpy of formation and entropy were determined for the purpose of predicting the phase diagram of Fe-V-O system. The properties of the different iron-vanadium oxides were studied and compared. Finally, Raman and IR frequencies were determined and compared to the existing experimental values.
The authors accurately predicted the phase diagram of Fe-V-O system at a temperature of 873K based on a combination of enthalpy of formation and entropy calculations. Iron-vanadium oxides FeV2O4 and FeV3O8 exhibited stronger anharmonicity compared to FeVO4 and Fe2V4O13 even though the latter group showed remarkably higher dynamical stability than the former, as indicated by the photon dispersions. The different vibration types were arranged from high to low frequencies. The authors observed that the high-frequency vibrations were dominated mostly by the V and O atoms due to the stronger V-O bonding. Furthermore, FeVO4 performed relatively better in terms of compressibility, stiffness, and physical strength properties. The low thermal conductivity of FeVO4 and Fe2V4O13 was attributed to the interactions between the low-lying optical and acoustic branches. It was worth noting that all the calculated Raman and IR frequencies were consistent with the experimental values.
In summary, the study investigated the thermodynamics lattice dynamical and elastic properties of iron-vanadium oxides from first-principles calculations. This approach proved feasible for investigating the physical and thermal properties of different types of iron-vanadium oxides. Based on the study results, the authors are confident that the insights revealed would provide fundamental material properties for iron-vanadium oxides for niche application such as the development of high-performance semiconductors.
Xie, W., Xing, X., & Cao, Z. (2020). Thermodynamic, lattice dynamical, and elastic properties of iron‐vanadium oxides from experiments and first principles. Journal of the American Ceramic Society, 103(6), 3797-3811.