PUBLICATION: M. Mihalkovic and M. Widom, "X-ray diffraction study and theoretical calculations on the X-phase Al9(Co,Ni)4", Phil. Mag. 86 (2005) p. 451-6 (reprint)
ABSTRACT: The structure of the X-phase was solved based on single-crystal X-ray diffraction data. The previously unknown ternary compound in the system Al.Co.Ni is representative of a new structure type with Pearson symbol mS26, lattice parameters a = 12.146(2) Å, b = 4.0702(5) Å, c = 7.652(1) Å, . = 105.88(1)°, V = 363.83(9) Å3, and spacegroup C2/m. The stability of the monoclinic structure and the Co/Ni ordering was studied by first-principles total-energy calculations. The lowest energy variant has composition Al18Co5Ni3. There are indications that the X-phase is an entropy-stabilized high-temperature phase.