Atomic‐scale microstructure of Hf 2 Al 4 C 5 ceramic synthesized by spark plasma sintering

A layered ternary carbide phase, Hf 2 Al 4 C 5 , 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. Hf 2 Al 4 C 5 crystal grains have elongated morphologies and are characterized with a high density of stacking faults with the insertion of additional (Al 4 C 3 ) or (HfC) units. Periodic stacking of Hf 2 Al 4 C 5 and HfAl 4 C 4 units along the [0001] direction is frequently observed in the Hf 2 Al 4 C 5 crystal, and it leads to the formation of Hf 4 Al 12 C 13 , which consists of 2/3 Hf 2 Al 4 C 5 unit cell and 1/2 HfAl 4 C 4 unit cell. In addition, Z‐shaped planar defects are observed in Hf 2 Al 4 C 5 grains, and the formation mechanism of the Z‐shaped defects was proposed as blocking effects of the Hf diffusion in Al 4 C 3 by pre‐existing {1‐101} pyramidal stacking faults in Al 4 C 3.