ELECTRIC-QUADRUPOLE INTERACTIONS AT CD-111 IN HFO2 AND ZRO2 - A PERTURBED-ANGULAR-CORRELATION STUDY

The electric hyperfine interactions of implanted In-111/Cd-111 probes in HfO2 and ZrO2 powder samples have been measured by means of perturb ed angular correlation (PAC) spectroscopy, in the temperature range be tween 15 K and 1273 K and at various oxygen pressures. In both oxides, several electric-field gradients (EFG) have been established that sho w pronounced similarities among the two oxides. The EFG having the lar gest fraction at room temperature has been assigned to the substitutio nal, defect-free cation site. Its quadrupole frequency upsilon(Q)=112 MHz and asymmetry parameter eta=0.6, at 300 K, are almost identical in both oxides. The scaling of this EFG relative to that found with Hf-1 81/Ta-181 probes in HfO2 confirms the substitutional site. EFG calcula tions with the point charge and the cluster model for this site are co mpared with each other and with the data. The other EFG's observed hav e been attributed to different charge states of oxygen neighbor ions. Below 120 K, the spectra are strongly damped and indicate dynamic quad rupole interactions.