Formation mechanism of Ti3SiC2 from a TiC lattice: An electron microscopic study

Titanium silicon carbide (Ti3SiC2, TSC) crystals with terraced morphology were prepared by heating a powder mixture consisting of Ti, Ti5Si3 and carbon nanotube (CNT). A sample containing an under-grown TSC crystal was analyzed by the HRTEM, showing various stacking patterns coexisted, including TSC, TiC, twined TiC, other intermediate stacking patterns, etc. A formation mechanism is proposed for the formation of TSC from a TiC lattice. The essential of the formation mechanism contains two steps: atom substitution and atom relocation. Atom substitution includes formation of carbon vacancy and insertion of Si atoms into the TiC lattice, and atom relocation involves position adjustments of C, Si and Ti atoms triggered by the atom substitution. It is illustrated that several atom substitutions and relocations on a starting TSC lattice result in a lattice pattern similar to the lattice observed in the HRTEM images. Lattice spacing values on the HRTEM images were also measured and analyzed, where the reduction of the standard deviation of the lattice spacing along a spatial direction confirmed the crystal growth path from the starting TiC to the product TSC.