Synthesis of La_(1-x)Sr_xMnO_3 powders by polymerizable complex method: Evaluation of structural, morphological and electrical properties

摘要

Lanthanum strontium manganite (La_(1-x)Sr_xMnO_3, LSM) powders were synthesized by polymerizable complex method, based on complexation of metal ions (MI) with citric acid (CA) and polyesterification between CA and ethylene glycol (EG). Firstly, the effect of the molar ratio of CA:MI (=1-3) was investigated on the synthesis of La_(0.7)Sr_(0.3)MnO_3 powders, which were characterized by thermal analysis (TGA/DTA), X-ray diffraction (XRD), and scanning electron microscopy (SEM). The results indicated that the molar ratio CA:MI = 3 is adequate for a good crystallization of pure perovskite phase after calcination, with nanometric crystallite sizes and porous microstructure. For the La_(0.7)Sr_(0.3)MnO_3 sample synthesized with CA:MI ratio of 3, it was investigated the effect of calcination temperature, showing that the perovskite structure is better crystallized at 900 °C, without secondary phase formation. Using this same CA:MI ratio and calcination temperature, powders with different Sr content (x = 0.2-0.4) were synthesized, with surface areas of 4-10m~2g~(-1). These powders were sintered at 1100 °C to produce porous pellets. The porosity of the sintered pellets and the electrical conductivity, measured by two-probe technique, increased with increasing Sr content.