Synthesis and Electronic Structure of a 3D Crystalline Stack of MXene-Like Sheets
Synthesis and Electronic Structure of a 3D Crystalline Stack of MXene-Like Sheets
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DOI：
10.1021/acs.chemmater.9b03722
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发表时间：
2019-12-10
影响因子：
8.6
通讯作者：
Warren, Scott C.
中科院分区：
文献类型：
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作者：
Druffel, Daniel L.;Lanetti, Matthew G.;Warren, Scott C.
尽管过去十年人们对 MXene 很感兴趣，但 MXene 通常是高度无序的，这可能会使它们的研究和使用变得复杂。例如，几乎所有 MXene 都具有表面末端（-O、-OH、-F）的随机混合物。此外，重新堆叠的 3D 薄膜具有乱层无序，并且层间通常含有离子、溶剂和其他物质。在这里，我们报道了 Y2CF2，一种层状晶体，其晶胞与 MXene 具有同构结构，其中各层仅被氟化物阴离子覆盖。我们通过高温固相反应直接合成3D晶体，这提供了高产率和纯度的3D晶体，并确保只有氟离子终止层。我们结合实验和计算技术来表征晶体结构和电子特性。我们发现相对较强的静电相互作用将各层结合在一起形成 3D 晶体，并进一步发现层之间缺乏轨道重叠，从而将 Y2CF2 描述为彼此电绝缘的类 MXene 片板。因此，我们认为 Y2CF2 是类 MXene 片材的纯 3D 晶体堆叠。此外，Y2CF2是第一个实验合成的过渡金属碳氟化物。我们希望这项工作能够激发对过渡金属碳化物氟化物的进一步探索，它可能是一类大而有用的组合物。
UDespite the interest in MXenes in the past decade, MXenes are often highly disordered, which can complicate their study and use. For example, nearly all MXenes have a random mixture of surface terminations (-O, -OH, -F). In addition, restacked 3D films have turbostratic disorder and often contain ions, solvent, and other species in between their layers. Here, we report Y2CF2, a layered crystal with a unit cell isostructural to a MXene, in which layers are capped only by fluoride anions. We directly synthesize the 3D crystal through a high-temperature solid-state reaction, which affords the 3D crystal in high yield and purity and ensures that only fluoride ions terminate the layers. We characterize the crystal structure and electronic properties using a combination of experimental and computational techniques. We find that relatively strong electrostatic interactions bind the layers together into a 3D crystal and further find that the lack of orbital overlap between layers gives rise to a description of Y2CF2 as slabs of MXene-like sheets electrically insulated from one another. Therefore, we consider Y2CF2 as a pure 3D crystalline stack of MXene-like sheets. In addition, Y2CF2 is the first transition metal carbide fluoride experimentally synthesized. We hope this work inspires further exploration of transition metal carbide fluorides, which are potentially a large and useful class of compositions.