Atomic dynamics in Al-rich Al-Co alloys near the composition of the decagonal quasicrystal - art. no. 214301

We used realistic Al-Co pair potentials [R. Phillips, J. Zou, A. E. Carlsso n, and M. Widom, Phys. Rev. B 49, 9322 (1994); J. A. Moriarity and M. Widom , ibid. 56, 7905 (1997)] to study the atomic dynamics of Al1-xTMx crystalli ne structures with the fractional content x of the transition metal (TM) at om x less than or similar to 0.3. Our list comprises rather simple structur es of Al3Ni and Al5Co2 alloys, complex structures related to the decagonal quasicrystal (Al9Co2Ni, O-Al13Co4), and a model of the crystalline approxim ant of the decagonal quasicrystal d-AlNiCo. Within the harmonic approximati on, we assess the impact of the structural complexity on the phonon density of states, sound velocity, Debye-Waller factor, and the character of the p honon states at low energies. In complex structures related to the decagona l quasicrystal, a significant fraction of low-energy vibrations have nonaco ustic, strongly localized character. In a molecular-dynamics annealing of t he decagonal approximant model performed at elevated temperature, a fractio n of aluminum atoms display signs of diffusive motion, while the equilibriu m positions of the cobalt atoms do not change.