Debye temperature at the fivefold- and threefold-symmetry surface of the Al-Pd-Mn quasicrystal

Abstract

Specular-beam intensity profiles are measured in low-energy electron diffraction as a function of temperature for the fivefold- and threefold-symmetry surfaces of the icosahedral quasicrystal Al-Pd-Mn. The resulting shifts of the Bragg-peaks to lower energies are accounted for mainly by a lattice expansion perpendicular to the surface and allow us to determine the thermal expansion coefficient of atomic layers to be (24.5 ± 2.0) × 10-6 K -1 for both surfaces. As a result of several measurements, a surface Debye temperature of 298 ± 7 K is found for the pentagonal and 301 ± 10 K for the threefold-symmetry surface. This similarity implies comparable bonding forces for the atoms at these surfaces. Additionally, the derived thermal expansion coefficient supports a layer-based structural model for both surfaces investigated here.