Concentration fluctuations induced by thermally‐driven local order changes in the molten binary alloy

Abstract

New universal relations are presented that connect the Darken stability with the constant pressure specific heat and the isothermal compressibility. They are the counterparts of the Ehrenfest‐Pippard relations in an extended form for 2nd‐order phase transitions in binary mixtures. The new relations make it possible that the contribution in the Darken stability caused by structural changes can be evaluated in terms of experimentally‐available thermodynamic response functions. The analysis for the Se‐Te and S‐Te systems shows that thermally‐driven local‐order changes cause segregation tendency on an atomic scale which can be large enough to cause divergent concentration fluctuations in the latter system. The unique closed loop miscibility gap localized in a small x‐T region, some 300 °C above the liquidus line, is a consequence of the change in the local order in the liquid.