Crystal structure of a new orthorhombic Al₇₂Pd₁₈Mn₅Si₅ approximant phase

Abstract

The structure of an orthorhmbic Al₇₂Pd₁₈Mn₅Si₅ phase was determined by single crystal X-ray diffraction: space group Pnma (No.148), a = 1.4396(3) nm, b = 2.4003(2) nm, c = 0.7603(2) nm, V = 2.6272(9) nm³, atoms/cell = 168, F(000) = 3341, μ = 7.355 mm⁻¹, D _calc = 4.613 Mgm⁻³, R(F) = 0.0312 for observed 3919 reflections measured by Mo-Kα radiation (λ = 0.071073 nm). The orthorhombic AlPdMnSi structure is well described by the stacking of a decagonal (0.72 nm) and pentagonal column (0.48 nm) along the b-axis. A new type of decagonal column structures with a periodicity of 1.2 nm (=0.48 + 0.72 nm) is proposed for the decagonal quasicrystals.

Keywords:

• X-ray diffraction
• crystal structure
• approximants
• AlPdMnSi
• decagonal column

Acknowledgements

The authors wish to express their gratitude to Y. Murakami, Institute for Materials Research, for his help with EPMA analysis. A part of this work was supported by a Grant-in-Aid for Challenging Exploratory Research (22656153) from the Japan Society for the Promotion of Science (JSPS).