Electron Diffraction Study of the Space Group Variation in the Al-Mn-Pt T-Phase

Binary high temperature Al3Mn (T-phase) and its extensions in ternary systems were the subjects of numerous crystallographic investigations. The results were ambiguous regarding the existence or lack of the center of symmetry: both Pna2(1) and Pnam space groups were reported. Our research on the Al-Mn-Pt T-phase allowed concluding that inside a continuous homogeneity region, the structure of the Al-rich T-phase (e.g., Al78Mn17.5Pt4.5) belongs to the non-centrosymmetric Pna2(1) space group, while the structure of the Al-poor T-phase (such as Al71.3Mn25.1Pt3.6) is centrosymmetric, i.e., Pnam. Following metallurgical and crystallographic considerations, the change in the symmetry was explained.

Automated summary

Binary high temperature Al3Mn (T-phase) and its extensions in ternary systems have been extensively studied in crystallography. The presence of a center of symmetry in these structures has been a topic of debate. Our research on the Al-Mn-Pt T-phase demonstrates that within a continuous homogeneity region, the Al-rich T-phase belongs to the non-centrosymmetric space group Pna2(1), while the Al-poor T-phase is centrosymmetric, specifically Pnam. This change in symmetry is explained based on metallurgical and crystallographic considerations.