Electric field gradients in 111In-doped (Hf/Zr)3Al2 and (Hf/Zr)4Al3 mixed compounds: ab initio calculations, perturbed angular correlation measurements and site preference

The quadrupolar hyperfine interactions of in-diffused probes in polycrystalline isostructural Zr4Al3 and Hf4Al3 samples containing small admixtures of the phases (Zr/Hf)3Al2 were investigated. A strong preference of 111In solutes for the contaminant (Zr/Hf)3Al2 minority phases was observed. Detailed calculations of the electric field gradient (EFG) at the Cd nucleus using the full-potential augmented plane wave + local orbital formalism allowed us to assign the observed EFG fractions to the various lattice sites in the (Zr/Hf)3Al2 compounds and to understand the preferential site occupation of the minority phases by the 111In atoms. The effects of the size of the supercell and relaxation around the oversized In and Cd probe atoms were investigated in detail.