The static magnetic hyperfine interaction and the hydrogen-induced dynamic electric quadrupole interaction (QI) at the nuclear probe Ta-181 on cubic Er sites in magnetically ordered C15 Laves-phase hydrides ErFe2Hx have been investigated by perturbed angular correlation (PAC) spectroscopy as a function of temperature (10 Kless than or equal toTless than or equal to600 K) and hydrogen concentration (0less than or equal toxless than or equal to3.2). At room temperature and concentrations x<2, the PAC spectra, supported by x-ray diffraction measurements, indicate the coexistence of two hydride phases ErFe2Hx with xless than or equal to0.1 and xsimilar to1.6-1.7, respectively, and a linear increase of the fraction of the high-concentration phase with increasing x. At low temperatures the PAC spectra of the high-concentration hydride reflect a broad distribution of strong static hyperfine interactions. The dynamic QI caused by rapidly diffusing H atoms becomes observable at T>400 K. The resulting Ta-181 nuclear quadrupole relaxation rates show an Arrhenius behavior with an activation energy of E-a=0.39(3) eV for x=1.5 and 2.0 and permit an estimate of the effective charge associated with the diffusing H atom of Z'eapproximate to0.095e. The vanishing time average of the nuclear quadrupole interaction in the fast-fluctuation region allows the separation of the magnetic and electric hyperfine interactions and the determination of the Ta-181 magnetic hyperfine field B-hf as a function of temperature and H concentration. At a given temperature Tgreater than or equal to450 K in the fast-fluctuation region, B-hf decreases with increasing x, indicating a decrease of the s conduction electron polarization at the probe site. The temperature dependence of B-hf in the fast-fluctuation region is also affected by the hydrogen concentration: at x=1.1, B-hf was found to decrease, at x=1.5 and 2.0 to increase with increasing T. Irreversible changes of the PAC spectra indicate that the thermal stability of crystalline ErFe2H2 encapsulated under vacuum is limited to Tless than or equal to550 K. ErH2 was identified by x-ray diffraction as one of the dissociation products, but there was no evidence for the precipitation of elemental Fe and a hydrogen-induced amorphization step.
