Positron lifetime measurements were made, as a function of temperature, in undoped and Sr-doped material. A second lifetime component, with a value of 225ps, developed above 100C. Its intensity grew sharply from 100 to 250C. The mean lifetime increased from 170 to 207ps as the temperature was increased from ambient to 300C. Using the results of a theoretical calculation of positron lifetimes at vacancies in this material, it was argued that the increase in lifetime with temperature was due to positron trapping at thermally generated La vacancies. Using a 2-state trapping model analysis, the formation energy was estimated to be 0.39eV.

Positron Lifetime Studies in Undoped and Sr Doped La2CuO4. C.S.Sundar, A.Bharathi, D.Vasumathi, Y.Hariharan: Materials Science Forum, 1992, 105-110, 1253-6