Guo Changjin, Zhu Jiajun, Liang Xiali, Wen Caifu, Xie Jiyang, Gu Chengding, Hu Wanbiao
Yunnan Key Laboratory of Electromagnetic Materials and Devices, National Center for International Research on Photoelectric and Energy Materials, School of Materials and Energy, Yunnan University, Kunming, P. R. China.
Electron Microscopy Center, Yunnan University, Kunming, P. R. China.
Nat Commun. 2024 Nov 22;15(1):10152. doi: 10.1038/s41467-024-54229-7.
CuInPS (CIPS) is an emerging 2D ferroelectric material known for disrupting spatial inversion symmetry due to Cu(I) position switching. Its ferroelectricity strongly relies on the Cu(I) atom/ion occupation ordering and dynamics. Nevertheless, the accurate Cu(I) occupations and correlated migration dynamics under the externally applied energy, which are key to unlocking ferroelectric properties, remain controversial and unresolved. Herein, an atomic-level direct imaging through aberration-corrected scanning transmission electron microscopy is performed to precisely trace the Cu(I) dynamic behaviours under electron-beam irradiation along (100)-CIPS. It clearly demonstrates that Cu(I) possesses multiple occupations, and Cu(I) could migrate to the lattice, vacancy, interstitial and interlayer sites between the InS octahedral skeletons of CIPS to form local CuInPS (x = 2-4) structure. Cu(I) multi-occupations induced lattice stress results in a layer sliding along the b-axis direction generating a sliding size of 1/6 b lattice constant. The CuInPS (x = 2-4) exists in a type of dynamic structure, only metastable with electron dose over 50 e Å, thus generating a dynamic process of , a completely unreported phenomenon. These findings shed light on the unveiled mechanism underlying Cu(I) migration in CIPS, providing crucial insights into the fundamental processes that govern its ferroelectric properties.
铜铟磷硫（CIPS）是一种新兴的二维铁电材料，因其铜（I）位置切换而破坏空间反演对称性而闻名。其铁电性强烈依赖于铜（I）原子/离子的占据有序性和动力学。然而，在外加能量下准确的铜（I）占据情况和相关的迁移动力学，这是开启铁电性能的关键，仍然存在争议且未得到解决。在此，通过像差校正扫描透射电子显微镜进行原子级直接成像，以精确追踪沿（100）-CIPS方向电子束辐照下铜（I）的动态行为。结果清楚地表明，铜（I）具有多种占据状态，并且铜（I）可以迁移到CIPS的InS八面体骨架之间的晶格、空位、间隙和层间位置，形成局部铜铟磷硫（x = 2-4）结构。铜（I）的多占据状态引起的晶格应力导致沿b轴方向的层滑动，产生1/6 b晶格常数的滑动尺寸。铜铟磷硫（x = 2-4）以一种动态结构存在，仅在电子剂量超过50 e Å时为亚稳态，从而产生一个完全未报道过的现象的动态过程。这些发现揭示了CIPS中铜（I）迁移的潜在机制，为控制其铁电性能的基本过程提供了关键见解。
