A point defect modelling study of the O non-stoichiometry of La2-xMxCuO4-y systems indicated that, whereas an O excess (y < 0) that was due to O interstitials predominated as x tended to zero, an O deficit (y > 0) resulted mainly from dopant-vacancy association at high x-values. Isolated O vacancies were apparently a minority defect species. The onset of an O deficiency that was due to dopant-vacancy association occurred when x was approximately equal to 0.15 and M was Ba or Sr. However, it occurred at x = 0.05 when M was Ca. An ideal ionic point defect behavior persisted up to an x-value of about 0.4 when M was Ba or Ca, and up to x = 0.5 when M was Sr.

L.Shen, P.A.Salvador, T.O.Mason: Journal of the American Ceramic Society, 1994, 77[1], 81-8