First-principles study of TiN/SiC/TiN interfaces in superhard nanocomposites

Heterostructures with one monolayer of interfacial SiC inserted between several B1(NaCl)-TiN (001) and (111) slabs are investigated in the temperature range of 0-1400 K using first-principles quantum molecular dynamics (QMD) calculations. The temperature-dependent QMD calculations in combination with subsequent variable-cell structural relaxation reveal that the TiN(001)/B1-SiC/TiN(001) interface exists as a pseudomorphic B1-SiC layer at temperatures between 0 and 600 K. After heating to 900-1400 K and subsequent static relaxation, the interfacial layer corresponds to a strongly distorted 3C-SiC-like structure oriented in the (111) direction in which the Si and C atoms are located in the same interfacial plane. The Si atoms form fourfold coordinated Si-C sub(3) N sub(1) configurations, whereas the C atoms are located in C-Si sub(3) Ti sub(2) units. All (111) interfaces calculated at 0, 300, and 1400 K have the same atomic configurations. For these interfaces, the Si and C layers correspond to the Si-C network in the (111) direction of 3C-SiC. The Si and C atoms are located in Si-C sub(3) N sub(1) and C-Si sub(3) Ti sub(3) configurations, respectively. The ideal tensile strength of all the heterostructures is lower than that of TiN. A comparison with the results obtained from earlier "static" ab initio density functional theory calculations at 0 K for similar heterostructures shows the great advantage of QMD calculations that reveal the effects of thermal activation on structural reconstructions.