Npj Comput. Mater.: 晶格点缺陷很小，但其可能搅动世界

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Fig. 1 The origin of the ferroelectricity in fluorite MO2 (M= Hf, Zr).

来自华中科技大学集成电路学院的董文副教授和傅邱云教授提出了缺陷诱导的极性声子带平坦化现象，通过分析掺杂La和仅掺杂VO的MO₂，所有掺杂情况都显示出明显平坦的极性声子带。与纯声子带相比，它们显著增强了极性声子带的平坦性，表明掺杂的MO₂中局域电偶极子的普及程度增加。

Fig. 2 Flat polar phonon bands in o-phase MO2 (M = Hf, Zr).

此外，在非平坦的极性声子带中没有明显的极化声子带，这意味着对极化的主要贡献来自于平坦的极性声子带。具有显著平坦声子带的掺杂MO₂中的准声子玻璃动力学可能表明薄膜中存在巨大的各向异性热整流效应，并启发高度集成电路的进一步设计。

Fig. 3 Point-defect-inducedflattening of phonon band structures in La-doped fluorite MO2 (M= Hf, Zr).

外延应变MO₂的极性声子带的平坦度与掺杂La的相比没有明显变化，这表明点缺陷在萤石MO₂的诱导/增强铁电性中起着更重要的作用。与纯o-MO₂中具有尖锐零宽度畴壁的局域电偶极子不同，在掺杂情况下，点缺陷诱导的局部对称性破坏导致点缺陷上的连续极化变化，使得畴壁弥散化。

Fig. 4 Effect of strain on the phonon band structure of the fluorite o-MO2 (M= Hf, Zr).

与仅掺杂Vo的情况相比，La-Vo缺陷对诱导显著更高的局部晶格畸变，具有显著平坦的极性声子带和通常更高的能垒，这表明适度的局部晶格失真和Vo对于实现高性能铁电性至关重要。作者的研究结果将从根本上推动萤石铁电体中感应铁电性的不足。缺陷驱动的平坦极性声子带也可能启发从原子水平研究新的掺杂诱导铁电系统中的铁电起源，例如掺杂的AlN、GaN和ZnO。

Point-Defect-Driven Flattened Polar Phonon Bands in Fluorite Ferroelectrics

Valery I. Levitas, Mehdi Kamrani & Biao Feng 

The scale-free ferroelectric polarization of fluorite MO2 (M=Hf, Zr) due to flat polar phonon bands are promising for nonvolatile memories. Defects are also widely introduced to improve the emergent ferroelectricity. However, their roles are still not fully understood at the atomic-level. Here, we report a significant effect of point-defect-driven flattening of polar phonon bands with more polar modes and polarization contribution in doped MO2. The polar phonon bands in La-doped MO2 (M=Hf, Zr) can be significantly flattened, compared with pure ones. However, the lower energy barrier with larger polarization of VO-only doped MO2 compared with La-doped cases suggest that VO and local lattice distortion should be balanced for high-performance fluorite ferroelectricity. The work is believed to bridge the relation between point defects and the generally enhanced induced ferroelectricity in fluorite ferroelectrics at the atomic-level and inspire their further property optimization via defect-engineering.