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

摘要

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 site-enthalpies. 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.