Carbon vacancies are commonly present in two-dimensional (2D) MXenes that hold promise in a variety of applications whereas their behavior remains unknown. Here we report on the influence of carbon vacancies on the structural stability, electronic properties and stiffness of MXenes by taking Ti₂CT₂ (T = O, F, and OH) as an example. According to the first-principles calculations, the formation energies of carbon vacancies in MXenes are lower than those in other typical 2D materials including graphene and MoS₂, in combination with high migration energies. These two features mean that carbon-vacant MXenes are thermodynamically and dynamically stable as further evidenced by the absence of structural reconstruction both in the ground state and at ambient temperature. Interestingly, carbon vacancies that are usually considered as defects substantially offer a new opportunity on at least two aspects: enhanced electronic conduction and reduced stiffness corresponding to improved flexibility. The localized states in the vicinity of the Fermi level introduced by carbon vacancies account for the prominent metallic characteristics in carbon-vacant Ti₂CT₂ MXenes.

中文翻译：

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Ti ₂ CT ₂ MXene中的碳空位：缺陷还是新的机会？

碳空位通常存在于二维（2D）MXene中，这些空位在各种应用中都有希望，但其行为仍然未知。在这里，我们以Ti ₂ CT ₂（T = O，F和OH）为例，报道碳空位对MXenes的结构稳定性，电子性能和刚度的影响。根据第一性原理计算，MXene中碳空位的形成能比石墨烯和MoS ₂等其他典型2D材料的低。，结合高迁移能。这两个特征意味着无碳的MXene具有热力学和动态稳定性，这进一步证明了在基态和环境温度下都没有结构重建。有趣的是，通常被视为缺陷的碳空位至少在两个方面提供了新的机会：增强的电子传导和降低的刚度（对应于提高的柔韧性）。碳空位引入的费米能级附近的局部状态解释了碳空的Ti ₂ CT ₂ MXenes的突出金属特性。