CRYSTALLOGRAPHIC CHARACTERIZATION OF SOME INTERMETALLIC COMPOUNDS IN THE AL-CR SYSTEM

Two Al-Cr compounds, known in the literature as the eta and epsilon phases, were studied by precession camera single crystal X-ray diffraction and transmission electron microscopy (TEM). The results are different from those reported in the literature. The epsilon Al4Cr phase was found to be hexagonal P6(3)/mmc, with lattice parameters a = 2.01 nm and c = 2.48 nm, and we suggest that it is isomorphous to the Al4Mn mu phase. The eta Al11Cr2 phase has a monoclinic (pseudo-orthorhombic) C-centered Bravais lattice with a3 congruent-to 1.76 nm, b3 congruent-to 3.05 nm, c3 congruent-to 1.76 nm, and beta congruent-to 90 deg and a possible C2/c space group. Single crystals of the eta phase are usually twinned.