Nonstoichiometry, structural perfection, and properties of La1-xMn1+xO3 +/-delta magnetoresistive materials

La1-xMn1+xO3+/-delta (-0.2 < x < 0.4) nonstoichiometric materials were char acterized by x-ray diffraction, density and magnetoresistance measurements, and nuclear magnetic resonance. The ceramics with Mn : La > 1 (x = 0, 0.1, 0.2, 0.3, 0.4) were found to be single-phase and to have a rhombohedral or orthorhombic perovskite structure. Comparison of x-ray and measured densit ies with various models of lattice defects suggests that the materials cont ain both anion and cation vacancies. The variations of resistivity and magn etoresistance with temperature, composition, and defect concentration are e xamined. A cluster model of mesoscopic inhomogeneities is proposed in which anion and cation vacancies and ions are assumed to be distributed in an or dered manner.