Atomic structure solution of the complex quasicrystal approximant Al77Rh15Ru8 from electron diffraction data.

Area of Science:

• Materials Science
• Crystallography
• Solid-State Chemistry

Background:

• Decagonal quasicrystals exhibit complex atomic arrangements.
• Understanding approximant phases is crucial for elucidating quasicrystal structures.
• Intermetallic compounds often display intricate and challenging crystal structures.

Purpose of the Study:

• To determine the crystal structure of the novel Al77Rh15Ru8 phase.
• To characterize this phase as an approximant of decagonal quasicrystals.
• To compare the structure with related phases in the Al-Rh-Ru system.

Main Methods:

• Automated electron diffraction tomography (ADT) combined with modern direct methods (MDM) for structure solution.
• Precession electron diffraction (PED) pattern analysis for structural validation.
• High-resolution transmission electron microscopy (HRTEM) for experimental verification.

Main Results:

• The Al77Rh15Ru8 E-phase was identified as orthorhombic (Pbma) with lattice parameters a = 23.40(5), b = 16.20(4), c = 20.00(5) Å.
• A complex structural model with 78 unique atomic positions (19 Rh/Ru, 59 Al) was established.
• The structure is characterized by hierarchical polyhedral packing and parallelogram tiling.

Conclusions:

• The Al77Rh15Ru8 E-phase represents one of the most complex intermetallic structures solved solely by electron diffraction.
• The determined structure provides insights into the relationship between approximant phases and quasicrystals.
• Structural comparison with the ε6-phase in Al-Rh-Ru systems was performed.