Observation of vacancies by positron trapping in cerium-doped zirconolites

Positron annihilation lifetime measurements on cerium-doped zirconolites ha ve given strong indications of positron trapping in samples that have previ ously been deduced to contain cation vacancies, mainly from X-ray absorptio n spectroscopy, thermogravimetry, and microanalysis. The increases in lifet ime of the majority lifetime component are similar to 20% for samples deduc ed to contain a few percent of vacant cation sites. Lanthanum-doped SrTiO3 samples, in which it is generally agreed that A-site vacancies are produced via the lanthanum doping, have been used as a model system and similar inc reases in lifetime have been observed for samples that contain more than si milar to 0.1 formula units of lanthanum.