High‐Resolution Transmission Electron Microscopy of Ti ₄ AlN ₃ , or Ti ₃ Al ₂ N ₂ Revisited

The structure and chemistry of what initially was proposed to be Ti 3 Al 2 N 2 are incorrect. Using high‐resolution transmission electron microscopy, together with chemical analysis, the stoichiometry of this compound is concluded to be Ti 4 AlN 3‐delta (where delta = 0.1). The structure is layered, wherein every four layers of almost‐close‐packed Ti atoms are separated by a layer of Al atoms. The N atoms occupy ∼97.5% of the octahedral sites between the Ti atoms. The unit cell is comprised of eight layers of Ti atoms and two layers of Al atoms; the unit cell is hexagonal with P 6 3 / mmc symmetry (lattice parameters of a = 0.3 nm and c = 2.33 nm). This compound is machinable and closely related to other layered, ternary, machinable, hexagonal nitrides and carbides, namely M 2 AX and M 3 AX 2 (where M is an early transition metal, A is an A‐group element, and X is carbon and/or nitrogen).

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