Determination of the crystal structure of the π-AlFeMgSi phase using symmetry- and site-sensitive electron microscope techniques

The crystal structure of the complex π-AlFeMgSi phase, which was previously thought to have the composition Al8FeMg3Si6, has been investigated. Microprobe analysis revealed that the phase has a different composition, Al9FeMg3Si5. The space group was determined and confirmed to be P\bar 62m with the use of parallel-beam electron diffraction (SAD) and convergent-beam electron diffraction (CBED). Owing to symmetry considerations the elements within the unit cell had to be rearranged. The rearrangement was confirmed using electron channelling. The z parameters of the elements were refined by examining the intensities from high-angle convergent-beam electron diffraction. Finally, the x parameters were adjusted slightly to arrive at acceptable interatomic distances.