STRUCTURE FACTORS AND BONDING IN BETA-NIAL

A combination of powder x-ray and critical voltage electron diffractio n was used to determine the lattice parameter and low-angle structure factors of stoichiometric beta NiAl, A weighted least squares fit meth od was used to obtain an accurate lattice parameter from the x-ray lin e position data, and the integrated intensities were carefully analyze d to determine the Debye-Waller factors; the latter were found to be i n good agreement with those obtained from the electron diffraction exp eriments. Highly accurate (errors congruent to 0.1%) low-angle structu re factors were also obtained from the electron diffraction measuremen ts, which were found to agree closely with first principles calculatio ns in the local density approximation. This information reveals that b onding in NiAl is mostly ionic with some covalent contribution.