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Revealing unusual rigid diamond net analogues in superhard titanium carbides

机译：揭示超硬碳化钛中不寻常的刚性金刚石网类似物

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Transition metal carbides (TMCs) are considered to be potential superhard materials and have attracted much attention. With respect to titanium and carbon atoms, we confirm the pressure-composition phase diagram of the Ti–C system using structure searches and first-principles calculations. We firstly discovered stable TiC _(4) which was expected to be synthesized at high pressure, as well as metastable TiC _(2) and TiC _(3) . These layered titanium carbides are diamond net analogues due to the unusual C-layers in the form of puckered graphene-like, diamond-like and double diamond-like C-layers. The existence of diamond-like C-layers might help to understand the formation of diamond. All the studied titanium carbides could be recoverable at ambient pressure and exhibited great mechanical properties (strong ability to resist volume and shear deformations, small anisotropy, and high hardness). Moreover, we crystallized the structure of TiC _(4) in other transition metal carbides and obtained five superhard TMC _(4) s (TM = V, Zr, Nb, Hf and Ta). Interactions between layers were revealed to be the source of the great mechanical properties and high hardness through combining detailed analyses of electronic structure and chemical bonding, namely, weak ionic interactions of neighboring Ti- and C-layers and the strong covalent interactions of C- and C-layers.
机译：过渡金属碳化物（TMC）被认为是潜在的超硬材料，受到了广泛的关注。关于钛和碳原子，我们使用结构搜索和第一性原理计算确定了Ti–C系统的压力组成相图。我们首先发现了稳定的TiC _（4）和亚稳态的TiC _（2）和TiC _（3），预期该稳定的TiC _（4）可以在高压下合成。这些层状碳化钛是金刚石网的类似物，这是由于以褶皱状石墨烯，金刚石和双层金刚石C层的形式存在不寻常的C层。类金刚石C层的存在可能有助于了解金刚石的形成。所有研究过的碳化钛都可以在环境压力下回收，并表现出出色的机械性能（抵抗体积和剪切变形的能力强，各向异性小，硬度高）。此外，我们在其他过渡金属碳化物中结晶了TiC_（4）的结构，并获得了五个超硬TMC_（4）s（TM = V，Zr，Nb，Hf和Ta）。通过对电子结构和化学键合的详细分析，即层间相邻的Ti和C层的弱离子相互作用以及C和C的强共价相互作用，对层之间的相互作用揭示了极好的机械性能和高硬度。 C层。

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