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

The crystal structure of the novel Al₇₇Rh₁₅Ru₈ phase (which is an approximant of decagonal quasicrystals) was determined using modern direct methods (MDM) applied to automated electron diffraction tomography (ADT) data. The Al₇₇Rh₁₅Ru₈ E-phase is orthorhombic [Pbma, a = 23.40(5), b = 16.20(4) and c = 20.00(5)Å] and has one of the most complicated intermetallic structures solved solely by electron diffraction methods. Its structural model consists of 78 unique atomic positions in the unit cell (19 Rh/Ru and 59 Al). Precession electron diffraction (PED) patterns and high-resolution electron microscopy (HRTEM) images were used for the validation of the proposed atomic model. The structure of the E-phase is described using hierarchical packing of polyhedra and a single type of tiling in the form of a parallelogram. Based on this description, the structure of the E-phase is compared with that of the ε6-phase formed in Al-Rh-Ru at close compositions.