Elham Ghiasi - School of Chemistry, Damghan University, ۳۶۷۱۶-۴۱۱۶۷, Damghan, Iran
Azim Malekzadeh - School of Chemistry, Damghan University, ۳۶۷۱۶-۴۱۱۶۷, Damghan, Iran

Nanosized LaMnO3+δ with particles size ~ 20 nm has been synthesized via citrate method [1]. The sample was characterized by XRD, BET, SEM and TEM analysis. The structural characterization of LaMnO3+δ by X-ray diffraction, X,pert package and Fullprof program provides evidence for a rhombohedral structure with 4% excess oxygen. The main defect type, especially known for LaMnO3, is based on cation vacancies defined by an oxygen excess. A high concentration of cation vacancies leads to a small anion conductivity [2]. The nonstoichiometry can increase the catalytic activity, but only in structures where Mn is defective. The unit cell parameters decrease with increasing of Mn4+ content. This effect can be correlated with an ionic radius smaller of Mn4+ (0.54 Å) into radius Mn3+ (0.64 Å) in the structure (Table 1). The cation vacancy improves the stability of LaMnO3.12 because the B-site ion is oxidated from unstable Mn3+ (?2?3??1) to the more stable Mn4+ (?2?3). It has been possible to evidence that LaMnO3.12 shows great catalytic activity, because of its small particle size, high surface area and also because its defect structure, are favourable for development of active sites [3].