PERTURBED-ANGULAR-CORRELATION STUDY OF CD-111 AND TA-181 NUCLEAR-QUADRUPOLE RELAXATIONS IN THE RARE-EARTH DIHYDRIDE DYH2+ -DELTA/

The static and dynamic electric quadrupole interaction (PI) of the nuc lear probes Cd-111 and Ta-181 on metal sites of the rare earth (RE) di hydride DyHx has been investigated as a function of temperature (19 le ss than or equal to T less than or equal to 900 K) and hydrogen concen tration (1.8 less than or equal to x less than or equal to 2.1) by per turbed angular correlation spectroscopy. It is shown that for non-RE n uclei with large quadrupole moments the dynamic QI caused by hopping h ydrogen may strongly exceed the magnetic dipole interaction with the f luctuating 4f magnetic moments. Measurements of the spin relaxation of suitable non-RE nuclei may therefore provide information on the hydro gen motion in the RE hydrides in spite of the strong 4f paramagnetism. The nuclear-quadrupole relaxation rates, however, were found to be st rongly affected by probe-impurity interactions. In DyHx the activation energy for jumps of hydrogen vacancies near the probe site, determine d from the temperature dependence of the dynamic perturb bation of the Cd-111 angular correlation, is E(a)=0.35(2) and 0.45(3) eV for x=1.96 and 1.99, respectively. The strength of the fluctuating QI of Cd-111: DyHx suggests an effective hydrogen charge of Z'similar to 0.6.