Metal-insulator transitions in anion-excess LaMnO<SUB>3+&#948;</SUB> controlled by the Mn<SUP>4+</SUP> content

LaMnO<SUB>3+&#948;</SUB> samples with Mn<SUP>4+</SUP> content up to 50% have been prepared by different methods. The structure of LaMnO<SUB>3+&#948;</SUB> changes from orthorhombic to cubic (via rhombohedral) with increase in the Mn<SUP>4+</SUP> content. LaMnO<SUB>3+&#948;</SUB> samples containing greater than 20% Mn<SUP>4+</SUP> are ferromagnetic and show resistivity maxima at a temperature T<SUB>t</SUB> which is close to the ferromagnetic Curie temperature. The resistivity maximum is due to the occurrence of a metal-insulator transition. In samples heated to the same temperature, the value of T<SUB>t</SUB> increases with % Mn<SUP>4+</SUP>. For a given sample, T<SUB>t</SUB> increases with the temperature of heat treatment due to the increase in particle size. The onset of ferromagnetism in LaMnO<SUB>3+&#948;</SUB> accompanied by an insulator-metal transition is similar to that found in La<SUB>1&#8722;x</SUB>Ca<SUB>x</SUB>MnO<SUB>3</SUB> and La<SUB>1&#8722;x</SUB>Sr<SUB>x</SUB>CoO<SUB>3