The structure of a new ternary aluminide Th 4Fe 3Al 32

Abstract

The atomic structure of a new ternary Th 4Fe 3Al 32 phase appearing in the alloy with composition Al–5 at.%Th–2.5 at.% Fe was solved using electron crystallography and X-ray diffraction techniques. Unit cell dimensions, type of Bravais lattice and the symmetry of the new compound were determined in transmission electron microscope by applying selected area and micro-beam electron diffraction techniques. The single-crystal X-ray diffraction data were used for developing the structural model. The Th 4Fe 3Al 32 compound crystallizes in a new type of crystal structure which is orthorhombic and belongs to Cmmm space group with the unit cell dimensions a = 10.03 Å, b = 16.44 Å and c = 8.21 Å. The unit cell contains 77 atoms which occupy 78 positions: 4i and 4j (for Th atoms), 4h and 2d (for Fe atoms) and 16r, 8m, 8n, 8q, 8p, 8o, 4g, 2b and 2c (for Al atoms). Refinement of the structure with isotropic thermal parameters for all atoms led to agreement factor R1 = 0.11. Refinement with anisotropic thermal parameters for Th atoms converged at R1 = 0.071.