Abstract It is well known that for a nanoparticle the solid-solid phase transition begins with the appearance of a high temperature disordered phase at the surface and the phase interface moves inward gradually with the increase of temperature. However, the size-dependent phase transition behavior remains unclear. Here we report an in-situ TEM study of the phase transition process of different-sized Ag2S nanoparticles at atomic resolution. The onset temperature of disordered phase of the small nanoparticle is found to be lower than that of the big nanoparticle. And, the disordered phase thickness of small nanoparticle is always thicker than that of big nanoparticle. By considering surface and interface free-energy, a phenomenological model based on the minimization of system free-energy is established, which could well explain our experimental results. These discoveries extend our understanding of size dependent phase transition mechanism.

中文翻译：

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Ag2S纳米颗粒的尺寸依赖性固-固相变过程

摘要 众所周知，纳米颗粒的固固相变开始于表面高温无序相的出现，随着温度的升高，相界面逐渐向内移动。然而，尺寸相关的相变行为仍不清楚。在这里，我们报告了原子分辨率下不同尺寸的 Ag2S 纳米粒子的相变过程的原位 TEM 研究。发现小纳米粒子的无序相的起始温度低于大纳米粒子的起始温度。并且，小纳米颗粒的无序相厚度总是比大纳米颗粒厚。通过考虑表面和界面自由能，建立了基于系统自由能最小化的现象学模型，这可以很好地解释我们的实验结果。这些发现扩展了我们对尺寸相关相变机制的理解。