Research on the origin of the thermodynamically stable amorphous phase in nm-sized particles

本研究从实验和热力学计算两个方面研究了纳米合金颗粒中热力学稳定非晶相的来源。首先，以锡铋系颗粒为研究对象，考察了表面和界面对纳米合金颗粒稳定性的影响。随着铋浓度的增加，末端TiN固溶体中约8 nm大小的颗粒直接转变为液相颗粒。另一方面，随着TiN浓度的增加，尺寸约为8 nm的末端铋固溶体颗粒首先转变为具有晶体/液体两相结构的颗粒，最终转变为液态颗粒。然而，即使在富铋一侧，大约5 nm大小的末端铋固溶体颗粒也直接变成了液体，而没有经历晶体/液体共存的阶段。这些实验结果在…上进行了讨论更多的是从热力学的角度来看。结果表明，纳米合金粒子的热力学稳定性不仅受表面影响，而且受界面影响。其次，用铅锡系颗粒考察了纳米颗粒中固溶体和液体的相对稳定性。通过在纳米纯铅颗粒上沉积TiN，在110℃时形成了约15 nm大小的铅-56at.%锡固溶体颗粒。这一事实表明，锡在15 nm大小的铅颗粒中的溶解极限几乎是锡在块状铅中的溶解极限(即10at%锡)的5倍。得到的结论如下：(1)在纳米合金颗粒中，由于表面和界面的原因，与晶相相比，液相变得相对稳定。(2)在纳米合金颗粒中，共熔点被抑制到甚至低于玻璃化转变温度的温度。这导致在这两个温度之间的温度范围内形成热力学稳定的非晶相。较少

In this research, the origin of the thermodynamically stable amorphous phase formed in nanometer-sized alloy particles was studied by both experiment and thermodynamic calculation.First, the effect of surface and interface on the stability of nanometer-sized particles was examined using particles of the Sn-Bi system. An approximately 8-nm-sized particle of the terminal tin solid solution directly changed into a particle of the liquid phase with increasing concentration of bismuth. On the other hand, an approximately 8-nm-sized particle of the terminal bismuth solid solution changed first to a particle with a crystal/liquid two-phase microstructure and eventually to a particle of the liquid phase, with increasing concentration of tin. Even in the bismuth-rich side, an approximately 5-nm-sized particle of the terminal bismuth solid solution, however, directly changed into the liquid phase, without taking a stage of crystal/liquid coexistence. These experimental results were discussed fro … More m a thermodynamic viewpoint. As a result, it was confirmed that not only surface but also interface is a governing factor of the thermodynamical stability of nanometer-sized alloy particles. Namely, the existence of the heterointerface between two crystalline solids stabilizes the liquid phase.Next, the relative stability of solid solution and liquid in nanometer-sized particles was examined using particles of the Pb-Sn system. Approximately 15-nm-sized particles of a lead-56at.%Sn solid solution were formed at 110℃ by tin deposition onto nanometer-sized pure lead particles. This fact indicates that the solubility limit of tin in 15-nm-sized lead particle is almost five times higher than the solubility limit of tin in bulk lead (i.e., 10at% Sn). It was confirmed that the relative stability between the highly concentrated solid solution and the amorphous phase governs the structure of nanometer-sized alloy particles.Conclusions obtained are given below.(1)In nanometer-sized alloy particles, the liquid phase becomes relatively stable as compared with the crystalline phase due to both surface and interface.(2)As a result, in nanometer-sized alloy particles the eutectic point becomes to be suppressed down to a temperature even below the glass transition temperature. This results in the formation of the thermodynamically stable amorphous phase over a temperature range between these two temperatures. Less