Understanding the mixing behaviour of elements in a multielement material is important to control its structure and property. When the size of a multielement material is decreased to the nanoscale, the miscibility of elements in the nanomaterial often changes from its bulk counterpart. However, there is a lack of comprehensive and quantitative experimental insight into this process. Here we explored how the miscibility of Au and Rh evolves in nanoparticles of sizes varying from 4 to 1 nm and composition changing from 15% Au to 85% Au. We found that the two immiscible elements exhibit a phase-separation-to-alloy transition in nanoparticles with decreased size and become completely miscible in sub-2 nm particles across the entire compositional range. Quantitative electron microscopy analysis and theoretical calculations were used to show that the observed immiscibility-to-miscibility transition is dictated by particle size, composition and possible surface adsorbates present under the synthesis conditions.

了解多元素材料中元素的混合行为对于控制其结构和性能非常重要。当多元素材料的尺寸减小到纳米尺度时，纳米材料中元素的混溶性通常会与其本体对应物发生变化。然而，对于这一过程缺乏全面和定量的实验洞察。在这里，我们探讨了 Au 和 Rh 的混溶性如何在尺寸从 4 到 1 nm 变化、成分从 15% Au 变化到 85% Au 的纳米颗粒中演变。我们发现，两种不混溶元素在尺寸减小的纳米颗粒中表现出相分离到合金的转变，并在整个组成范围内以亚 2 nm 颗粒的形式完全混溶。定量电子显微镜分析和理论计算用于表明观察到的不混溶到混溶转变取决于合成条件下存在的颗粒尺寸、组成和可能的表面吸附物。