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 Al₄C_3. [ABSTRACT FROM AUTHOR]