Site preferences of indium impurity atoms in intermetallics having Al₃Ti or Al₃Zr crystal structures

Abstract

Site-fractions of indium impurity probe atoms occupying up to three inequivalent Al-sites in Al₃Ti, Al₃V and Al₃Zr phases were measured using perturbed angular correlation of gamma rays (PAC). Sites were identified via characteristic nuclear quadrupole interactions. Ratios of site-fractions were measured in thermal equilibrium in the range 600 to 1,210 K. Arrhenius plots of the ratios were fitted with thermally activated expressions, yielding differences in vibrational entropies and siteenthalpies. Enthalpy differences were greatest for Al₃Zr, ∼0.22 eV, and smaller for Al₃Ti and Al₃V, which is correlated with the excess volume of the transition-metal atom over the Al-atom, Vibrational entropy differences were small, in the range 0 to −0.25 kB.