Synthesis, structures, chemical bonding, and properties of Al9–xFexMo3 with 0.5 ≤ xFe ≤ 1.8

Abstract

We report the crystal structure and properties of the Al9–xFexMo3 phases. Samples with nominal xFe content up to 2.5 were synthesized by arc-melting and annealed at 600 °C. The products were analyzed by ex situ and in situ X-ray diffraction, and the phase compositions were determined. The crystal structures of the ternary phases were refined at room temperature. The τ1 phase, Al8.5Fe0.5Mo3, crystallizes in the tetragonal Al3Ti type of structure, whereas an orthorhombic distorted structure is observed for Al9–zFezMo3 with 1.0 ≤ zFe ≤ 1.8. At temperatures around ≈300 °C, a reversible orthorhombic ↔ tetragonal phase transition occurs. The τ2 phase (disordered W-type of structure) is metastable at room temperature and decomposes above ≈425 °C into the Fe-enriched orthorhombic Al9–zFezMo3 phase, AlFe, and AlMo3. DFT calculations of the formation energies of FeAl substitution are reported, and aspects of chemical bonding in Al9–xFexMo3 are provided (DOS, COHP, and ELF). The physical properties are investigated by 57Fe-Mössbauer spectroscopy and magnetic measurements, indicating spin glass behavior at low temperatures.