Lattice imaging of metastable TiSi₂

The microstucture of metastable C49-TiSi₂ was studied by high-resolution transmission electron microscopy in a bilayer thin film of Ti and Si annealed at 700 °C. Large grains (300-400 nm) of C49-TiSi₂ phase with high density of stacking faults on (010) planes were observed. A preferred orientation among the C49-TiSi₂ grains was identified, and the grains were aligned along the [010] with slight misorientation. The diffraction pattern from the metastable TiSi₂ showed continuous streaks superimposed by discrete spots along hk0 reciprocal lattice rows, indicating the presence of polytypism. Lattice imaging of polytypic TiSi ₂ has been obtained and it showed that the structure is nonperiodic and one dimensionally disordered due to the stacking faults. The finding of metastable TiSi₂ associated with polytypism suggests that its structure could be conveniently represented by various stackings of atomic planes along the [010] direction. An atomic model is proposed to explain the origin of polytypism. It is shown that the arrangement of atoms in C49-TiSi ₂ structure has four equivalent positions.