Lifetime spectra of positrons in lowly La-doped BaTiO3

A study on positron lifetimes in lowly La-doped ceramic BaTiO3, which has semiconduction, is reported. The experiment results show that the lifetimes τ1 and τ2 decrease first and increase after, the intensity I2 increases first and decreases after with increasing amount of La, and these parameters turn at the same X value. The changes of τ1, τ2 and I2 below the turn result from increasing of Ba vacancies with increasing La. To explain the results a complex defect (Ba vacancy + La ion complex) model was proposed. The experimental results show that this complex defect dose not trap positrons