Electric field gradients in Zr8Ni21 and Hf8Ni21 intermetallic compounds; results from perturbed angular correlation measurements and first-principles density functional theory

Numerous technological applications of Ni-based Zr and Hf intermetallic alloys promoted comprehensive studies in Zr8Ni21 and Hf8Ni21 by perturbed angular correlation (PAC) spectroscopy, which were not studied earlier until this report. The different phases produced in the samples have been identified by PAC and X-ray diffraction (XRD) measurements. Using 181Hf probe, two non-equivalent Zr/Hf sites have been observed in both Zr8Ni21 and Hf8Ni21 compounds. From present PAC measurements in Zr8Ni21, a component due to the production of Zr7Ni10 by eutectic reaction from the liquid metals is also observed. The phase Zr7Ni10, however, is not found from the XRD measurement. In Zr8Ni21, while the results do not change appreciably up to 973 K exhibit drastic changes at 1073 K. In Hf8Ni21, similar results for the two non-equivalent sites have been found but site fractions are in reverse order. In this alloy, a different contaminating phase, possibly due to HfNi3, has been found from PAC measurements but is not found from XRD measurement. Density functional theory (DFT) based calculations of electric field gradient (EFG) and asymmetry parameter (η) at the sites of 181Ta probe nucleus allowed us to assign the observed EFG fractions to the various lattice sites in (Zr/Hf)8Ni21 compounds.