Vacancy defects inPbTiO3and lanthanide-ion-dopedPbTiO3: A study of positron lifetimes

Abstract

Positron lifetime measurements were performed on lanthanide- (Ln) ion-doped ${\text{PbTiO}}_{3}$ and identified the presence of both Pb vacancy, ${V}_{\text{Pb}}$, and Ti vacancy, ${V}_{\text{Ti}}$, 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 ${V}_{\text{Pb}}$-related defects, consistent with donor ion substitution at the Pb site. By contrast, increasing the concentration of Dy ions decreased the ratio of ${V}_{\text{Pb}}$- to ${V}_{\text{Ti}}$-related defects. The behavior is attributed to the incorporation of ${\text{Dy}}^{3+}$ ions as acceptors at Ti sites. Density-functional theory calculations of positron lifetimes for vacancy complexes, and relaxed structure monovacancy defects, in ${\text{PbTiO}}_{3}$ are reported and support the vacancy-defect assignments.