  La1-xCaxMnO3+delta and La1-xNaxMnO3+delta samples with well defined cation
molecularity and oxygen contents are analyzed with XRPD, electrical
conductivity, electron paramagnetic resonance and static magnetization
measurements. Point defects are introduced in the structure by: i) aliovalent
cation doping (substitutional defects), ii) oxygen over-stoichiometry (cation
vacancies) and iii) oxygen under-stoichiometry (oxygen vacancies). The cation
doping mainly influences the material by affecting the tolerance factor and the
oxidation of the Mn ions; the cation vacancies affect the magnetic properties
by interrupting the interaction paths between Mn4+-Mn3+ ions whereas the oxygen
vacancies have a stronger influence on the structural and electrical properties
and act on the magnetic properties by the overall decrease on the Mn4+ amount
and by the creation of sample regions with different magnetic features. We can
state that the basic magnetic and electrical behaviors of the Ca- and Na-doped
lanthanum manganite compounds are driven from the Mn4+-Mn3+ ratio and all the
peculiar behaviors are indeed caused by defects, concentration gradient and,
more generally, by lattice disorder.
