Solute-solute interactions in intermetallic compounds

TL;DR

This study investigates solute-solute interactions in GdAl2 intermetallic compounds using PAC, revealing the nature and enthalpies of interactions between In and Ag solutes on different sublattices.

Contribution

It provides detailed measurements of solute interactions and site preferences in GdAl2, highlighting the effects of Ag addition on solute behavior and site transfer enthalpies.

Findings

Repulsive interactions for In/Gd/+Ag/Gd/ and In/Gd/+Ag/Al/ pairs.

Slightly attractive interaction for In/Al/+Ag/Al/ pairs.

Transfer enthalpy of Ag-solutes from Gd- to Al-sites is temperature dependent.

Abstract

Two types of solute-solute interactions are investigated in this work. Quadrupole interactions caused by nearby Ag-solute atoms were measured at nuclei of 111In/Cd solute probe atoms in the binary compound GdAl2 using the method of perturbed angular correlation of gamma rays (PAC). Locations of In-probes and Ag-solutes on both Gd- and Al-sublattices were identified by comparing site fractions in Gd-poor and Gd-rich GdAl2(Ag) samples. Interaction enthalpies between solute-atom pairs were determined from temperature dependences of observed site fractions. Repulsive interactions were observed for close-neighbor complexes In/Gd/+Ag/Gd/ and In/Gd/+Ag/Al/ pairs, whereas a slightly attractive interaction was observed for In/Al/+Ag/Al/. Interaction enthalpies were all in the range +/- 0.15 eV. Temperature dependences of site fractions of In-probes on locally defect-free Gd- and Al-sites yields a transfer enthalpy that was found to be 0.343 eV in a previous study of undoped GdAl2. The corresponding values in GdAl2(Ag) samples are much smaller. This is attributed to competition of In- and Ag-solutes to occupy sites of the same sublattice. While the difference in site-enthalpies of In-solutes on Gd- and Al-sites is temperature independent, it is proposed that the transfer of Ag-solutes from Gd- to Al-sites leads to a large temperature dependence of degeneracies of levels available to In-solutes, resulting in an effective transfer enthalpy that is much smaller than the difference in site-enthalpies.