揭示文石 CaCO3 内的晶体缺陷。,Proceedings of the National Academy of Sciences of the United States of America

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揭示文石 CaCO3 内的晶体缺陷。
Proceedings of the National Academy of Sciences of the United States of America ( IF 9.4 ) Pub Date : 2022-03-31 , DOI: 10.1073/pnas.2122218119
Xingyuan San _{1,

2} , Mingyu Gong ₃ , Jian Wang ₄ , Xiuliang Ma ₂ , Roberto Dos Reis _{5,

6} , Paul J M Smeets _{5,

6} , Vinayak P Dravid _{5,

6} , Xiaobing Hu _{2,

5,

6}

Affiliation

了解文石（CaCO3 的三种结晶多晶型物之一）的变形机制对于了解珍珠质整体优异的机械性能至关重要。位错滑移和变形孪晶以前被认为是文石中的塑性载体，但对位错和孪晶的晶体学特征知之甚少。在这里，利用各种透射电子显微镜技术，我们揭示了孪晶、部分位错和相关堆垛层错的原子结构。结合拓扑模型和密度泛函理论计算，我们识别了完整的孪晶元素、孪晶断开特征以及相应的孪晶剪切角（∼8.8°），并对独特的部分位错进行了合理化。此外，我们揭示了文石内一种未报道的势能耗散模式，即通过部分位错的堆积形成纳米晶。通过对生物文石和非生物文石的微观结构比较，我们发现双胞胎的晶体学特征是相同的。然而，由于结晶条件差异很大，非生物文石中的孪晶密度要低得多，而这又可能是由于缺乏有机物、高温和压力差、无机杂质的变化或其组合所致。我们的研究结果丰富了关于适应文石塑性变形的内在晶体缺陷的知识，并为设计具有更好强度和韧性的生物工程材料提供了见解。

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Uncovering the crystal defects within aragonite CaCO3.

Knowledge of deformation mechanisms in aragonite, one of the three crystalline polymorphs of CaCO3, is essential to understand the overall excellent mechanical performance of nacres. Dislocation slip and deformation twinning were claimed previously as plasticity carriers in aragonite, but crystallographic features of dislocations and twins have been poorly understood. Here, utilizing various transmission electron microscopy techniques, we reveal the atomic structures of twins, partial dislocations, and associated stacking faults. Combining a topological model and density functional theory calculations, we identify complete twin elements, characters of twinning disconnection, and the corresponding twin shear angle (∼8.8°) and rationalize unique partial dislocations as well. Additionally, we reveal an unreported potential energy dissipation mode within aragonite, namely, the formation of nanograins via the pile-up of partial dislocations. Based on the microstructural comparisons of biogenic and abiotic aragonite, we find that the crystallographic features of twins are the same. However, the twin density is much lower in abiotic aragonite due to the vastly different crystallization conditions, which in turn are likely due to the absence of organics, high temperature and pressure differences, the variation in inorganic impurities, or a combination thereof. Our findings enrich the knowledge of intrinsic crystal defects that accommodate plastic deformation in aragonite and provide insights into designing bioengineering materials with better strength and toughness.

更新日期：2022-03-31

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