Helium defectoscopy of cerium gadolinium ceramics Ce$_{0.8}$Gd$_{0.2}$O$_{1.9}$ with a submicrocrystalline structure in the impurity disorder region

The concentration of impurity anion vacancies formed upon the dissociation of gadolinium-vacancy complexes has been determined using helium defectoscopy of the cerium gadolinium ceramics Ce$_{0.8}$Gd$_{0.2}$O$_{1.9}$ with a submicrocrystalline structure in the temperature range $T$ = 740–1123 K and at saturation pressures ranging from 0.05 to 15 MPa. It has been found that the energy of dissociation of gadoliniumvacancy complexes is $E^D_{\mathrm{eff}}$ = 0.26 $\pm$ 0.06 eV, and the energy of dissolution of helium in anion vacancies in the impurity disorder region is $E^P$ = -0.31 $\pm$ 0.09 eV. The proposed mechanism of dissolution has been confirmed by the investigation of the electrical conductivity of the cerium gadolinium ceramics, as well as by the high-speed molecular dynamics simulation of the dissociation of gadolinium-vacancy complexes. It has been assumed that a decrease in the effective dissolution energy in comparison with the results of the previously performed low-temperature investigations is caused by the mutual repulsion of vacancies formed upon the dissociation of gadolinium-vacancy complexes in highly concentrated solutions of gadolinium in CeO$_2$ with increasing temperature.