Laser ablated La0.5Sr0.5CoO3-δ thin films have been studied by Doppler-broademng-detected positron annihilation using a variable-energy positron beam. The oxygen partial pressure during cooling from the growth temperature was altered through the range 760 torr to 10−5 torr to change the oxygen non-stoichiometry of the films.
The measured Doppler broadened lineshape parameter S was found to increase with increasing oxygen nonstoichiometry. For films cooled with an oxygen partial pressure of ≤ 10−4 Torr positron trapping to monovacancy type defects is infered. It is proposed that Sr ion oxygen vacancy complexes are likely trapping sites.
For the film cooled in 10−5 torr oxygen the magnitude of the increase in S, with respect to that measured from the film cooled in 760 Torr oxygen, showed positron trapping to vacancy cluster defects is occuring.