Observation of Vacancies by Positron Trapping in Cerium-Doped Zirconolites

Positron annihilation lifetime measurements on cerium-doped zirconolites have given strong indications of positron trapping in samples that have previously been deduced to contain cation vacancies, mainly from X-ray absorption spectroscopy, thermogravimetry, and microanalysis. The increases in lifetime of the majority lifetime component are ∼20% for samples deduced 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 increases in lifetime have been observed for samples that contain more than ∼0.1 formula units of lanthanum.