The reassessment of the structural transition regions along the liquidus of Fe-Si alloys and a possible liquid-liquid structural transition in FeSi2 alloy

We reassessed the structural transition regions along the liquidus of Fe-Si alloys by using ab initio molecular dynamics simulation. Except for 50 at.% Si, structural transition compositions are found at both 30 at.% Si and 67 at.% Si (FeSi2) which are eutectic alloys. We demonstrated that the liquid structure in the sub-region of 0∼30 at.% Si is close-packed, and in the sub-region of 67∼100 at.% Si liquid alloys have very open structure. From 30 at.% Si to 67 at.% Si, the close-packed structure gradually change into open one. These structure transition sub-regions are also supported by the formation enthalpy of liquid alloys. Furthermore, the predicted enthalpy change between 1585 K and 1873 K is so large that there is probably liquid-liquid transition with temperature at FeSi2 alloy which is an important thermoelectric material. Discussions have been made on the materials phenomenon of several Fe-Si alloys based on the structural information.