Crystal structures of the Al–Ti–Pt τ5 and τ6 phases solved by zonal precession electron diffraction

The earlier reported Al–Ti–Pt phases τ 5 and τ 6 were studied using Precession Electron Diffraction (PED) and Convergent Beam Electron Diffraction (CBED). Their atomic models were proposed applying Direct Methods to the PED zonal data. The τ 5 -phase (FeCr-type, P 4 2 / mnm , a = 9.702 and c = 5.023 A) can be described by the formula Al 2 Ti 5 Pt 3 , positioning 18 Ti, eight Pt and four Al atoms at five unique atomic positions in the unit cell. The τ 6 -phase ( P 2 1 3, a = 6.8477 A) can be described by the formula Al 3 Ti 5 Pt 2 . Its unit cell consists of 20 atoms at 12 b and two 4 a atomic positions occupied by Ti, Pt and Al atoms, respectively. Due to deviation from the stoichiometry, the τ 6 -phase can be related to a defect variant of the Au 4 Al-type structure. The structures of the studied phases are presented as the stacking of coordination polyhedra.