Phase transition is a physical phenomenon that attracts great interest of researchers. Although the theory of second-order phase transitions is well-established, their atomic-scale dynamics in polycrystalline materials remains elusive. In this work, second-order phase transitions in polycrystalline Cu₂Se at the transition temperature are directly observed by in situ aberration-corrected transmission electron microscopy. Phase transitions in microcrystalline Cu₂Se start at the grain boundaries and extend inside the grains. This phenomenon is more pronounced in nanosized grains. Analysis of phase transitions in nanocrystalline Cu₂Se with different grain boundaries demonstrates that grain boundary energy dominates unsynchronized phase transition behavior. This suggests that the energy of grain boundaries is the key factor influencing the energetic barrier for initiation of phase transition. The findings advance atomic-scale understanding of second-order phase transitions, which is crucial for the control of this process in polycrystalline materials.

中文翻译：

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多晶 Cu2Se 中晶界主导的非同步相变的原子尺度观察

相变是一种引起研究人员极大兴趣的物理现象。尽管二阶相变理论已经确立，但它们在多晶材料中的原子尺度动力学仍然难以捉摸。在这项工作中，通过原位像差校正透射电子显微镜直接观察到多晶 Cu ₂ Se 在转变温度下的二级相变。微晶 Cu ₂ Se 中的相变始于晶界并延伸到晶粒内部。这种现象在纳米级晶粒中更为明显。_{纳米晶 Cu 2}中的相变分析具有不同晶界的硒表明晶界能量主导非同步相变行为。这表明晶界能量是影响相变起始能量势垒的关键因素。这些发现促进了对二级相变的原子级理解，这对于控制多晶材料中的这一过程至关重要。