Origin of the looped two-melt phase in the liquid S-Te system

Recently established new thermodynamic relations among experimentally avail able data are used to evaluate the contribution of the structural change in the liquid S-Te system to the Darken stability. The analysis of the Darken stability shows that the unusual looped two-melt phase separation that tak es place in a small composition interval well above the liquidus line is a consequence of the change in the local order of the liquid. Delicate balanc e between the entropy term and the contribution from the structural change realizes this unique two-melt phase separation. This local order change tha t is expected in a small composition range has actually been observed by ne utron diffraction measurements.