Vacancy defects in PbTiO3 and lanthanide-ion-doped PbTiO3: A study of positron lifetimes

Positron lifetime measurements were performed on lanthanide- (Ln) ion-doped PbTiO3 and identified the presence of both Pb vacancy, V-Pb, and Ti vacancy, V-Ti, related point defects. Increasing the concentration of Ln ions La to Eu resulted in an increase in the dominant contribution to the positron lifetime spectrum from V-Pb-related defects, consistent with donor ion substitution at the Pb site. By contrast, increasing the concentration of Dy ions decreased the ratio of V-Pb- to V-Ti-related defects. The behavior is attributed to the incorporation of Dy3+ ions as acceptors at Ti sites. Density-functional theory calculations of positron lifetimes for vacancy complexes, and relaxed structure monovacancy defects, in PbTiO3 are reported and support the vacancy-defect assignments.