Ca^(2+)和Sr^(2+)共掺杂钴铁酸镧的合成及电性能

Electrical properties and preparation Ca^(2+)and Sr^(2+) co-doped lanthanum iron cobaltite

以金属硝酸盐为原料,氨水为沉淀剂,共沉淀法合成了中温固体氧化物燃料电池阴极材料La0.7Sr0.3-x CaxCo0.9 Fe0.1 O3-δ(简称: LSCCF,x= 0. 05、0.10、0. 15、0. 20)系列纳米晶粉料。TG DSC、XRD和SEM研究了LSCCF粉料的合成条件、晶体结构和颗粒粒度形貌。实验表明: LSCCF 粉料形成经过脱水、LaCoO3 基氧化物形成和LSCCF固溶体形成等过程;前驱体800℃处理4h就可形成单一钙钛矿型结构的固体氧化物。使用直流四极探针法在空气气氛下测试了1200℃烧结3h 后所有LSCCF 样品从100 ~800℃时的电导率,结果显示随着测量温度的提高,电导率逐渐增大,并在490℃时达到最大值,随后逐渐降低。490℃范围内,Ca2+ 和Sr2+ 共掺杂取代La3+ 进入晶格后,其导电机制符合小极化子绝热孔隙理论。而当Ca2+的掺杂含量x=0.10 或0.15 时,Ca2+和Sr2+共掺杂在450 ~ 800℃范围对LSCCF 的电导率产生“混合”效应,致使电导率值基本保持一致。且所有样品在600~800℃的电导率都超过400S/cm,满足阴极材料对电性能的要求。

La0.7Sr0.3-xCaxCo0.9 Fe0.1O3-δ (LSCCF, x = 0.05-0.20) nanocrystalline powders as the cathode materials for intermediate temperature solid oxide fuel cells were synthesized by chemical co-precipitation method using metal nitrates as starting materials and ammonia water as precipitant. The formation process, the crystal structure and the particle size micrograph of LSCCF powders were investigated with DSC-TG, XRD and SEM. The experimental results show that the formation process of LSCCF in heating can be divided into dehydration decomposition of reactants, formation of LaCoO3 based oxides and formation of doped LSCCF solid solution. Calcined the powders at 800°C for 4 h all of single perovskite phase can be obtained. The electrical conductivity of the specimens sintered at 1200°C for 3 h was measured by the four-probe DC method in the temperature range from 100°C to 800°C in air. With the measuring temperature rising, the conductivity increases and reaches to the peak value at 490°C then gradually decreases. The conduction mechanism was attributable to the adiabatic-hopping of small polarons below 490°C and the mixing effects caused by substituting Sr2+ and Ca2+ for La3+ at x = 0.10 or 0.15 for LSCCF lead to the electrical conductivity being basically equal over 450°C. Otherwise the electrical conductivity of all doped specimens was higher than 400 S/cm from 600°C to 800°C, which can meet the electrical properties demands for the cathode materials.