Temperature - and composition - driven changes in site occupation of indium solutes in Gd

Fractional concentrations of indium solutes at Gd sites and Al sites in the Laves phase Gd113xAl223x were measured for different temperatures and sample compositions using perturbed angular correlation spectroscopy. At fixed composition, the fraction of indium on Gd sites was observed to decrease as temperature was increased. At fixed temperature, the fraction of indium on Gd sites was observed to increase as the composition became more deficient in Gd. The trends are explained using a thermodynamic model that couples solute site occupation with concentrations of point defects. The increase in enthalpy of the crystal when indium switches from a Gd site to an Al site was determined to be 0.343~7! eV.