Al13Os4-type monoclinic phase and its orthorhombic variant in the Al-Co alloy system

A C-centered monoclinic phase isotypic with Al13Os4 and structurally related to it body-centered orthorhombic phase were found in the Al13Co4 alloy annealed at 1373 K and subsequently quenched. The new orthorhombic phase exhibits the lattice parameters of a = 1.531 nm, b = 1.235 nm and c = 0.758 nm. The minor monoclinic phase is imbedded in the orthorhombic matrix as a twinned structure with branched needle-like morphology. The interface between these mutually oriented phases contains a dense arrangement of the mismatch dislocations.