Perturbed-angular-correlation study of electric quadrupole interactions in nanocrystallineZrO2

The electric quadrupole interaction (QI) of ${}^{181}\mathrm{Ta}$ on Zr sites of nanocrystalline ${\mathrm{ZrO}}_2$ prepared by crystallite condensation, oxidation, and in situ compaction was investigated by perturbed-angular-correlation (PAC) measurements which show the existence of three components with different QI parameters. The dominant contribution to the PAC spectra is characterized by a broad distribution of strong axially asymmetric electric-field gradients, suggesting a highly disordered oxygen environment of the Zr sites in the nanocrystallites in addition to a distribution of probe sites in the crystallite interfaces. The other two PAC components correspond to monoclinic and tetragonal ${\mathrm{ZrO}}_2$. The thermal evolution of the phases in nanocrystalline ${\mathrm{ZrO}}_2$ was studied by isochronal annealing between 290 K and 1500 K. The complete transformation of the disordered component to the monoclinic phase requires an annealing temperature of $T_A=1400\mathrm{}\hspace{0.5em}\mathrm{K}$, indicating that complete defect recovery occurs only after a martensitic transformation cycle through the high-temperature tetragonal phase.