Atomic-scale microstructure of Hf2Al4C5 ceramic synthesized by spark plasma sintering

A layered ternary carbide phase, Hf2Al4C5, was successfully synthesized by spark plasma sintering method. Detailed (atomic-scale) microstructure of the ternary carbide was investigated by aberration-corrected scanning transmission electron microscopy and atomic-resolution energy dispersive X-ray spectroscopy. Hf2Al4C5 crystal grains have elongated morphologies and are characterized with a high density of stacking faults with the insertion of additional (Al4C3) or (HfC) units. Periodic stacking of Hf2Al4C5 and HfAl4C4 units along the [0001] direction is frequently observed in the Hf2Al4C5 crystal, and it leads to the formation of Hf4Al12C13, which consists of 2/3 Hf2Al4C5 unit cell and 1/2 HfAl4C4 unit cell. In addition, Z-shaped planar defects are observed in Hf2Al4C5 grains, and the formation mechanism of the Z-shaped defects was proposed as blocking effects of the Hf diffusion in Al4C3 by pre-existing {1-101} pyramidal stacking faults in Al4C3.