Structural models of τ2-inflated monoclinic and orthorhombic Al-Co phases

A structural model of the C-centered monoclinic Al3Co, previously called tau(2)-Al13Co4 (a = 3.984 nm, b = 0.8148 nm, and c = 3.223 nm; beta = 107.97 deg), with a and c parameters about tau(2) times (tau = (1 + root 5)/2 = 1.61803...) larger than the corresponding ones in the C-centered monoclinic Al13Co4 (a = 1.5183 nm, b = 0.8122 nm, and c = 1.2340 nm; beta = 107.90 deg), has been derived from its high resolution electron microscopy (HREM) image and the known structure of the monoclinic Al13Co4. The simulated [010] HREM image and electron diffraction pattern agree reasonably well with the experimental results. Based on this structural model, the powder X-ray diffraction pattern was indexed. Furthermore, a structural model of the newly found tau(2)-inflated orthorhombic phase (a = 3.79 nm, b = 0.81 nm, and c = 3.22 nm) was also proposed.