Structure of Ti4AlN3 - a layered M(n+1)AX(n) nitride

Recent high resolution transmission electron microscopy and electron probe X-ray microanalysis show that the compound originally thought to be Ti3Al2N 2 is Ti4AlN3. In this paper we report on the crystal structure determinatio n by Rietveld refinement on neutron and X-ray powder diffraction data. Ti4A lN3 crystallizes with a hexagonal unit cell, space group P6(3)/mmc, and wit h lattice parameters a = 2.9880(2) and c = 23.372(2) Angstrom. The stacking sequence is such that every four layers of Ti atoms is separated by a laye r of Al atoms. The N atoms occupy octahedral sites between the Ti atoms mak ing up a network of corner shared octahedra. This compound is closely relat ed to other layered, ternary, machinable, hexagonal nitrides and carbides, namely, M2AX and M3AX2, where M is an early transition metal, A is a A-grou p element and X is either C and/or N. (C) 2000 Elsevier Science Ltd. All ri ghts reserved.