Electric field gradient in transition metal amorphous alloys

The mean atomic configurations in Hf- and Zr-based amorphous alloys prepared by different routes were studied using the perturbed angular correlations (PAC) technique. For all the as-prepared amorphous samples, the PAC spectra are well described by a wide distribution of frequencies revealing atomic configurations around the probes compatible with those in a dense random packing of ions (DRP). The measured electric field gradient strength Vzz seems to be independent of the preparation method and of the addition of second phase nanoparticles (CaO and ZrC) for the same early transition metal content. The Vzz values observed in Hf based alloys are systematically higher than that in Zr-based alloys of similar composition and show a greater variation with composition. These behaviors are discussed in terms of the different contributions to the EFG, its dependence with the density of states at the Fermi level and in comparison with similar trends observed in binary amorphous alloys. Also, the Ta probe role on the measured Vzz in Hf and Zr systems was analyzed.