Solute-solute interactions in intermetallic compounds studied using perturbed angular correlation of gamma rays
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Interactions between pairs of solute atoms dissolved in a binary intermetallic compound were studied. Perturbed angular correlation of gamma rays (PAC) was used to detect solute atoms next to impurity PAC probe atoms in GdAl2 through measurements of nuclear quadrupole interactions. Interaction enthalpies between 111In probe atoms and 1 at.% of Ag, Cu, Au, or natural In solutes were measured and found to be in the range ±0.20 eV, similar to values observed in studies of solute pairs in pure metals by Krzysztof Królas et al. in the 1980s. Some expected solute pairs were not observed, presumably because their nuclear quadrupole interactions could not be resolved from other signals. Results for Ag-doped GdAl2 which previously appeared in Hyperfine Interactions 238:18 (2017) (Appendix A), have been updated with an improved analysis methodology, but without major changes in deduced interaction enthalpies. New results are presented for In, Cu, and Au solutes. A previous study of undoped GdAl2 (Phys. Rev. B69, 174202 (2004)) showed that, with increasing temperature, dilute 111In probes transfer from the Gd- to Al-sublattice with an activation enthalpy of 0.343(7) eV. This can be viewed as a two-level system, where the transfer enthalpy is the difference in site enthalpies of the probe plus the formation enthalpy of an antisite defect. It was found that 1 at.% of In, Ag, Au, or Cu reduced the effective transfer enthalpy to zero. This implies that solute atoms compete with 111In to transfer to the Al-sublattice with increasing temperature, effectively decreasing the degeneracies of sites available to probe atoms. These degeneracies are correlated with the width of the GdAl2 phase field, suggesting that the phase boundary compositions are at 33.3 at.% Gd and ~32 at.% Gd. Transfer and segregation enthalpies for 111In probes in GdNi2 were published in Hyperfine Interactions 238:17 (2017) (Appendix B). New analysis suggests that Cu-solutes cluster near 111In probe atoms, but signals for discrete solute pairs could not be resolved. Experiments are underway to combine diffusion measurements of Cd-tracer atoms and PAC measurements of jump frequencies in Al3Er to determine the correlation coefficient for impurity diffusion for the first time.