Positron annihilation lifetime spectroscopy in titanate ceramics

Abstract

Positron annihilation lifetimes increase from 0.17 ns to 0.25 ns when 0.05 formula units of alkaline earth vacancies exist in BTi03 perovskites [1 ,2], where B = Ca or Sr, and that are doped with trivalent rare earths R substituting for B ions, according to the agreed model of B(la 3x/2)Rx0 x/2Ti03 (0 = vacancy). However this state of affairs is not reproduced when B = Ba, so 5, Ba vacancies do not appear to be the main means of charge compensation for substitutional R ions in this case. However in this latter situation there is a small increase of a PALS spectral component having a lifetime of 0.3 ns, characteristic of a small number of Ba vacancies, upon s doping with Gd ions. The effects of other doping schemes employing rare earth doping of Ba titanate wil be discussed.