Gd掺杂EuO和EuS相稳定性的第一性原理研究
First-principles study of phase stability of Gd-doped EuO and EuS
摘要：
采用第一性原理计算结合标准集团展开方法和蒙特卡罗模拟，构建了Eu $_{1-x}$ Gd $_x$ O和Eu $_{1-x}$ Gd $_{x}$ S准二元合金体系的等电子相图.该氧化物体系在富Gd侧具有较宽的扩散间隙，但在富Eu侧形成有序化合物，在生成焓图中表现出深的不对称凸包。硫化物体系没有稳定的化合物。氧化物和硫化物化合物的形成能力的巨大差异是由于局部晶格弛豫的贡献，这是敏感的阴离子的大小。Gd在EuO和EuS中的溶解度在室温下在10-20%的范围内，并且在更高的温度下迅速增加，这表明可以在没有第二相沉淀的情况下产生高度掺杂的无序固溶体。我们还预测，在适当的实验条件下，岩盐钆可以稳定。
英文摘要：
Phase diagrams of isoelectronic Eu$_{1-x}$Gd$_x$O and Eu$_{1-x}$Gd$_{x}$S quasi-binary alloy systems are constructed using first-principles calculations combined with the standard cluster expansion approach and Monte-Carlo simulations. The oxide system has a wide miscibility gap on the Gd-rich side but forms ordered compounds on the Eu-rich side, exhibiting a deep asymmetric convex hull in the formation enthalpy diagram. The sulfide system has no stable compounds. The large difference in the formation enthalpies of the oxide and sulfide compounds is due to the contribution of local lattice relaxation, which is sensitive to the anion size. The solubility of Gd in both EuO and EuS is in the range of 10-20% at room temperature and quickly increases at higher temperatures, indicating that highly doped disordered solid solutions can be produced without the precipitation of secondary phases. We also predict that rocksalt GdO can be stabilized under appropriate experimental conditions.
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