The HfAl 2 and ZrAl 2 Laves phases studied by 181Ta and 111Cd perturbed angular correlation spectroscopy

Abstract

Using perturbed angular correlation (PAC) spectroscopy and 181Hf/ 181Ta and 111In/ 111Cd radioactive probes, the electric field gradients (EFGs) in the ZrAl 2 and HfAl 2 Laves phases were measured in the temperature range 20–1100 K. In both matrices, 181Hf was found to substitute at the unique Hf/Zr site. In the ZrAl 2 compound, the 111In probes were assigned to the two Al sites. The relative fractions of the corresponding EFGs indicate a strong preference of these impurities in favor of the 2( a) Al site over the 6( h) Al site. In the HfAl 2 compound, the 111In impurities substitute for Hf up to 370 K and reach the Al sites only above 420 K. In both compounds and for both radioactive probes, the temperature dependence of the quadrupole interaction frequencies was measured. It is interesting to note that, for 181Ta in both compounds, they increase with temperature.