Xu Chunhong, Bao Kuo, Ma Shuailing, Li Da, Duan Defang, Yu Hongyu, Jin Xilian, Tian Fubo, Liu Bingbing, Cui Tian
State Key Laboratory of Superhard Materials, College of Physics, Jilin University Changchun 130012 China
RSC Adv. 2018 Apr 18;8(26):14479-14487. doi: 10.1039/c8ra00400e. eCollection 2018 Apr 17.
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 which was expected to be synthesized at high pressure, as well as metastable TiC and TiC. 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 in other transition metal carbides and obtained five superhard TMCs (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.
过渡金属碳化物（TMCs）被认为是潜在的超硬材料，并已引起广泛关注。关于钛和碳原子，我们通过结构搜索和第一性原理计算确定了Ti-C体系的压力-组成相图。我们首次发现了有望在高压下合成的稳定TiC，以及亚稳的TiC和TiC。这些层状碳化钛是类金刚石网络类似物，这是由于存在呈褶皱状类石墨烯、类金刚石和双类金刚石形式的异常C层。类金刚石C层的存在可能有助于理解金刚石的形成。所有研究的碳化钛在常压下均可恢复，并表现出优异的力学性能（抵抗体积和剪切变形的能力强、各向异性小且硬度高）。此外，我们在其他过渡金属碳化物中确定了TiC的结构，并获得了五种超硬TMCs（TM = V、Zr、Nb、Hf和Ta）。通过结合电子结构和化学键的详细分析，揭示了层间相互作用是优异力学性能和高硬度的来源，即相邻Ti层和C层之间的弱离子相互作用以及C层和C层之间的强共价相互作用。
