Iron-based superconductors have attracted attention because of their high critical temperature (T_c). Among iron-based superconductors, BaFe₂As₂ is expected to be used as polycrystalline magnets in high magnetic fields. In polycrystalline High-T_c superconductors such as BaFe₂As₂, to improve the superconducting performance, it is essential to predict and control the formation of polycrystalline microstructures. Generally, polycrystalline BaFe₂As₂ is fabricated by solid-state sintering. Since the microstructure formation during the solid-state sintering is a complex phenomenon depending on the heat treatment conditions, computational methods are useful for predicting the microstructure formation processes.

Phase-field method has been used as the effective computational method for microstructure evolutions during the solid-state sintering. Using the phase-field method with accurate physical property values and parameters such as interfacial properties, quantitative results can be obtained. These values of simple metals can be obtained by experiments. However, the experiments to obtain these values for new materials require special and advanced equipment and techniques. On the other hand, using the first-principles calculation, physical property values can be obtained from an electronic state of materials without experimental data. Physical property values calculated by the first-principles calculation are expected to be accurate. Therefore, phase-field simulation with improved accuracy is anticipated using the first-principles calculation.

The purpose of this study is to construct a multi-scale computational method to improve the accuracy of phase-field simulation of microstructure evolutions using the physical properties calculated by the first-principles calculation. The computational method developed in this study is implemented in solid-phase sintering of BaFe₂As₂. The surface energy of BaFe₂As₂ is calculated by the first-principles calculation and the anisotropy functions are constructed. Then, this anisotropy function is applied to the phase-field simulations of solid-state sintering.