Decagonal quasicrystal in the Al–Pd–Mn system

Abstract

A stable decagonal quasicrystal in Al₇₀Pd_30−xMn_x alloys (x = 10–20) was examined by electron diffraction and high-resolution electron microscopy. The decagonal quasicrystalline grains are formed with definite crystallographic relationships to adjacent icosahedral and Al₃Mn crystalline grains. The structure of the decagonal phase, which is formed as the main phase at near Al₇₀Pd₁₀Mn₂₀ composition, is a mixture of decagonal quasicrystalline regions with some linear phason strain and microcrystalline regions. The structures of both regions may be interpreted in terms of quasiperiodic and periodic tilings, constructed with two types of bond lengths, S (about 2 nm) and L (= τ · S, where τ is the Golden ratio), of the same atom cluster with decagonal symmetry.

Key Words:

• Decagonal quasicrystal
• quasicrystal
• high-resolution electron microscopy
• X-ray diffraction
• Al-Pd-Mn