  In this paper we report studies on the correlation between the presence and
distribution of cation vacancies in doped manganites (La,M)MnO3+delta (where M
= Na, Ca) and their magnetic properties. Results indicate that cation vacancies
are distributed differently for the different crystal structures and dopant ion
type. In particular it is shown that knowledge of the total vacancies
concentration alone is not enough to fully characterize the physical properties
of manganites and that their distribution between the A and B sites of the
perovskite structure plays a crucial role which should be taken into account in
future studies.
