Anwar Jamshed, Leitold Christian, Peters Baron
Department of Chemistry, Lancaster University, Lancaster LA1 4YW, United Kingdom.
Department of Chemical and Biomolecular Engineering, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
J Chem Phys. 2020 Apr 14;152(14):144109. doi: 10.1063/5.0003224.
Solid solutions, structurally ordered but compositionally disordered mixtures, can form for salts, metals, and even organic compounds. The NaCl-KCl system forms a solid solution at all compositions between 657 °C and 505 °C. Below a critical temperature of 505 °C, the system exhibits a miscibility gap with coexisting Na-rich and K-rich rocksalt phases. We calculate the phase diagram in this region using the semi-grand canonical Widom method, which averages over virtual particle transmutations. We verify our results by comparison with free energies calculated from thermodynamic integration and extrapolate the location of the critical point. Our calculations reproduce the experimental phase diagram remarkably well and illustrate how solid-solid equilibria and chemical potentials, including those at metastable conditions, can be computed for materials that form solid solutions.
固溶体是结构有序但成分无序的混合物，可形成于盐类、金属甚至有机化合物中。NaCl-KCl体系在657℃至505℃之间的所有成分下都能形成固溶体。在低于505℃的临界温度下，该体系呈现出混溶间隙，同时存在富钠和富钾的岩盐相。我们使用半巨正则维登方法计算该区域的相图，该方法对虚拟粒子嬗变进行平均。我们通过与热力学积分计算得到的自由能进行比较来验证我们的结果，并外推临界点的位置。我们的计算结果与实验相图非常吻合，说明了如何为形成固溶体的材料计算固-固平衡和化学势，包括亚稳态条件下的化学势。
