High-resolution transmission electron microscopy of Ti4AlN3, or Ti3Al2N2 revisited

The structure and chemistry of what initially was proposed to be Ti3Al2N2 a re incorrect. Using high-resolution transmission electron microscopy, toget her with chemical analysis, the stoichiometry of this compound is concluded to be Ti4AlN3-6 (where delta = 0.1). The structure is layered, wherein eve ry four layers of almost-close-packed Ti atoms are separated by a layer-of Al atoms. The N atoms occupy similar to 97.5% of the octahedral sites betwe en 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 P6(3)/mmc symmetry (lattice parameters of a = 0.3 nm and c = 2.33 nm), This compound-is machi nable 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 tra nsition metal, A is an A-group element, and X is carbon and/or nitrogen).