Ta4AlC3:: Phase determination, polymorphism and deformation

Ta4AlC3, a new member of the M(n+1)AX(n)-phase family, has been synthesized and characterized (n = 1-3; M = early transition metal; A = A-group element; and X = C and/or N). Phase determination by Rietveld refinement of synchrotron X-ray diffraction data shows that Ta4AlC3 belongs to the P6(3)/mmc space group with a and c lattice parameters of 3.10884 +/- 0.00004 angstrom and 24.0776 +/- 0.0004 angstrom, respectively. This is shown to be the alpha-polymorph of Ta4AlC3, with the same structure as Ti4AlN3. Lattice imaging by high-resolution transmission electron microscopy demonstrates the characteristic MAX-phase stacking of alpha-Ta4AlC3. Three modes of mechanical deformation of alpha-Ta4AlC3 are observed: lattice bending, kinking and delamination. (c) 2007 Published by Elsevier Ltd on behalf of Acta Materialia Inc.