Mechanically activated low temperature synthesis of Sr doped lanthanum manganite

Alkaline earth doped lanthanum manganites (La1-x M-x Mn O3+delta, with M=Ca, Sr, Ba ...) are attracting materials because of their peculiar properties displayed in giant magnetoresistance and electrocatalytic activity. Classical synthesis routes of the material make use of solid state reaction, among suitable precursors, at temperatures generally above 900 - 950 degrees C. However such temperatures promote morphological and microstructural characteristics, such as low surface area and large particle size, lowering the catalytic activity. Mechanosynthesis technique has been therefore attempted on a mixture of La2O3, MnO2 and SrCO3 in order to verify the possibility of obtaining La0.7Sr0.3MnO3 with high specific area and small grain size. LaMnO3 has been also synthesized in the same way for comparison. The behavior of the mixtures has been monitored by x-ray diffraction. Thermogravimetry (TG) and differential thermal analysis (DTA) have been used to follow the thermal behavior compared to that of simply blended mixture. TG and DTA thermograms indicate that the synthesis of manganite, already present in the milled samples, is completed at temperatures much lower (650 - 700 degrees C) than those of conventional routes. Preliminary measurements of specific surface area confirm that mechanically activated synthesis of lanthanum manganite is able to produce powders having higher surface area and smaller particle size than those obtained by conventional solid state reactions.