Lattice locations of dilute indium solute atoms in phases having the ${\mathrm{Ni}}_2{\mathrm{Al}}_3$ crystal structure were determined using the technique of perturbed angular correlations of $\gamma$ rays. Four sites, including two inequivalent group IIIA sites, a group VIII site, and an empty-lattice site, were distinguished by measurement of nuclear quadrupole interactions at ${}^{111}\mathrm{In}∕\mathrm{Cd}$ probes in the phases ${\mathrm{Ni}}_2{\mathrm{Ga}}_3$, ${\mathrm{Pt}}_2{\mathrm{Ga}}_3$, ${\mathrm{Ni}}_2{\mathrm{Al}}_3$, ${\mathrm{Pd}}_2{\mathrm{Al}}_3$, and ${\mathrm{Pt}}_2{\mathrm{Al}}_3$. Occupied sites were identified by comparison with quadrupole interactions of probes in three indides having the same structure, ${\mathrm{Ni}}_2{\mathrm{In}}_3$, ${\mathrm{Pd}}_2{\mathrm{In}}_3$, and ${\mathrm{Pt}}_2{\mathrm{In}}_3$, and by calculations of electric-field gradients at the four sites. Probes were observed to “switch” sites as the composition changed from being rich to poor in the transition metal (TM). Indium was observed to exclusively occupy one of the group III sites in TM-rich gallides and aluminides. In TM-poor gallides, indium occupied the TM sublattice, while near the stoichiometric composition it also partially occupied the empty-lattice site, which has interstitial character. For TM-poor aluminides, highly inhomogenous quadrupole interactions were observed indicating that indium was located on irregular sites in lattice sinks such as grain boundaries. Dependences of site fractions on composition are interpreted using a thermodynamic model that relates fractions of solutes on substitutional, interstitial, and lattice-sink sites to concentrations of intrinsic defects. Heuristic rules are presented which describe site-selection behavior based on the experiments and model. Among other rules, it was found that there is a maximum tendency for solutes to occupy interstitial sites near the stoichiometric composition.

• Received 18 August 2003

DOI:https://doi.org/10.1103/PhysRevB.70.024202