The vacancy concentrations cv in B2-type alloys of Ni1-xAlx (x = 0.45 to 0.54) and Co1-xAlx (x = 0.46 to 0.52) were determined by the measurements of lattice constant with X-ray diffraction and bulk density ρA using the Archimedes method. The measurements were performed at room temperature for various sizes of powder samples. The obtained density of ρA increased with decreasing powder size, and the resultant vacancy concentration decreased. The size dependence of ρA and a scanning electron microscopic observation indicated that the increase in ρA was due to the presence of voids in the powder samples. The reliable values of cv were estimated using a model that reduced the influence of voids. The effective formation energies of vacancy and antistructure atom were also estimated from the composition dependence of cv. The results of the estimation showed that the Al antistructure was the ground state of the defect structure at 0 K.

Influence of Voids on the Accuracy of Measurement of Vacancy Concentration in NiAl and CoAl Intermetallic Compounds. T.Kodera, M.Matsui, T.Takama: Japanese Journal of Applied Physics, 2004, 43[5A], 2607-11