溶胶凝胶——燃烧法合成La_(0.7)Sr_(0.3)MnO_3阴极材料及其性能

Synthesis and properties of La_(0.7)Sr_(0.3)MnO_3 cathode powder by sol-gel combustion

低温合成钙钛矿单相La0.7Sr0.3MnO3粉体,以降低粒度、提高活性,已成为本领域研究的一个新方向。采用溶胶凝胶-燃烧法合成La0.7Sr0.3MnO3粉体,讨论了溶胶体系pH值和柠檬酸用量对燃烧程度及相组成的影响。利用络合理论,计算了溶胶体系的pH值对于络合物的影响。实验结果表明,当pH<3时,溶胶凝胶体系稳定存在;而当pH达到3有白色沉淀出现。燃烧完全程度随着pH值的增加和柠檬酸用量的减少而提高。晶相合成程度以柠檬酸/硝酸盐比值(j)=0.5时最为完全,随着j提高,生成微量第二相。1300℃烧结试样以j=1.5最为致密,电导率峰值达150S/cm。综合考虑相组成和性能两因素,运用此法制备La0.7Sr0.3MnO3粉体时,j以1.5为宜。

The interesting of low temperature preparing single-phase perovskite powders to obtain fine grain size and high sinterability has steadily increased recently. La0.7Sr0.3MnO3 powder was synthesized by sol-gel combustion method in this paper. The influences of pH and citric acid content on the stability of the sol system, the combustion degree and the phase formation were investigated. The ionic distribution of La3+, Sr2+ and Mn2+ at different pH values was calculated to determine the suitable pH for the sol system. White precipitates appeared at pH≥3.0, while the sol was clear and transparent at pH < 3. It was found that the combustion was improved with increasing pH when pH value was below 3 and decreasing citric acid content. No second phase was found at low ratio of citric acid to nitrates (j=0.5) and small amount of second phase occurred with increasing j to above 1. A dense sample was obtained under the conditions of high j value (1.5) and 1 300 ℃ sintering temperature. The electrical conductivity of samples was measured by DC four-probe method. It was demonstrated that conductivity enhanced with increasingj, having a maximum of 150 S/cm for the dense sample. It was revealed that an optimal j was 1.5 when considering both phase formation and sinterability of the powder.