Self-propagation High Temperature Synthesis Of Lanthanide Complex Oxide Cathode Material For Fuel Cell

A1-xBxMnO3(A is a rare-earth element, B is an alkaline earth metal) are of high technological importance because of their interesting electronic and magnetic properties. More recently, the perovskite manganite compounds, La1-xSrxMnO3 have been used as the cathode of the solid oxide fuel cell(SOFC) because of their electro-ion conductivity properties. In manganite perovskites, substitution of divalent ions (alkaline earth metals viz. Ca, Sr, Ba) in the A sublattice, introduces Mn4+ ions or holes into the system. It is generally considered that the concentration of holes is equal to the concentration of divalent cations because of the charge compensation by controlled valencies.A number of publications exist in the literature on the synthesis of manganite perovskites. Recently, Stephanie et al. published a review on porous manganese oxide materials. It discussed the various known techniques for the preparation of La1-xSrxMnO3 and other manganese oxide materials. Here, we report a novel self-propagation high temperature synthesis (SHS) method for the preparation of manganite perovskites, involving a redox reaction. This method helps to retain higher-oxidation states Mn ions in the system. Thereby, modifying the electronic and magnetic properties. Various perovskite compositions includes La2O3- SrO2-Mn- KMnO4- NaClO4 H2O, La2O3- SrO2- Mn- KMnO4 and La2O3- SrCO3- Mn-KMnO4- NaClO4 H2O have been prepared through this method and their structure, electronic and magnetic properties have been studied.In the course of SHS, the content of liquid phase plays an important role in it, and the content of oxidant and dilution and the temperature of heat treatment can influent the phase and the size of the product. But the density of the samples have little influence on the SHS course and the product phase.From the three systems above, it is obvious that in La2O3- SrO2- Mn-KMnO4- NaClO4 H2O system the purity of La1-xSrxMnO3 is the best when the content of KMnO4 y=0.5 and in La2O3- SrO2 Mn- KMnO4 system the purity of La1-xSrxMnO3 is the best when y=0.6, however, in La2O3- SrCO3- Mn- KMnO4-NaClO4 H2O system the product includes amount of impurity, which infers that SrO2 has played an inevitable role.Through the mechanism study of La2O3- SrO2- Mn- KMnO4- NaClO4 H2O system and La2O3- SrO2- Mn- KMnO4 system, it can be found that the system give off some water and some Mn be oxidized before 200 C, KMnO4 decompose at 275 C, SrO2 decompose at about 360C and NaClO4 decompose at about 450 C. The main product La1-xSrxMnO3 begin to form at 425 C. It is continuous that KMnO4, SrO2, NaClO4 oxidize Mn, so the main product phase has enough time to perfect.The La1-xSrxMnO3 powder has been sintered by constant pressure sintering, heat pressure sintering(HP) and spark plasma sintering(SPS). The result shows that the SPS is the best one when the temperature is 900 C, the density of sample is the best.Through the study of electric and magnetic properties, it can be known that while x=0.3, the electric conductivity of La1-xSrxMnO3 is 88S-cm-1, Hc=173.34oe, Ms=8066.27A/m, Mr=469.70A/m.