Positron annihilation spectroscopic studies on Nd-doped ceria

We report a new result on the characterization of Nd-doped ceria, Ce1−xNdxO2−x/2 (image) using positron lifetime spectroscopy (LTS) and coincidence Doppler broadening (CDB) measurements. A systematic increase in lifetime that is attributed to formation of Nd-oxygen vacancy associates is seen from image–0.4 followed by a sharper increase up to image. The change in profile of lifetime around image suggests drastic increase in the concentration of these associates. Discontinuity in lifetime around image is ascribed to ordering of oxygen vacancies. Coincidence Doppler broadening measurements indicate reduction in the overlap of positron wavefunction with oxygen core electrons due to trapping of positrons. Low-temperature (50–300 K) lifetime measurements indicate the presence of Rydberg-like positron states associated with Nd3+ sites.