Investigation of Sm_0.2Ce_0.8O_1.9/Na₂CO₃Nanocomposite Electrolytes: Preparation, Interfacial Microstructures, and Ionic Conductivities

With the analytical grade Ce(NO3)3·6H2O, Sm(NO3)3·6H2O, and Na2CO3 as starting materials, Sm0.2Ce0.8O1.9(SDC)/Na2CO3 nanocomposite electrolytes were prepared through a rare-earth/sodium carbonate complex precipitation, prefiring, and sintering operations. The phase components and microstructures were studied and characterized by XRD, FESEM, TEM, and TG-DSC. In particular, the interfacial interactions between the phases of SDC crystallites and amorphous Na2CO3 were deliberately probed by Raman and infrared spectroscopies. It has been found that the amorphous carbonates in the SDC/Na2CO3 composites are tightly bound to the surface of SDC nanocrystals to form an intimate shell-layer via a long-range interface interaction, characterized by ∼8 nm in thickness and a red-shift of 15 cm(-1) for the Raman symmetrical vibration mode of carbonate ions with reference to the crystalline Na2CO3, which is practically enabled to frustrate the crystallization of Na2CO3 and enhance the transport properties of oxide ions in the SDC/Na2CO3 composite electrolytes because of the disordered interface microstructures. Moreover, smaller SDC nanocrystals were found to achieve higher conductivity enhancements for the SDC/Na2CO3 composite electrolytes and the {100} facets on the surface of SDC nanocrystals are believed to be more important than the other facets because of their strong electropositivity. This effect makes the SDC/Na2CO3 composite sample prefired at 600 °C realize a much higher ionic conductivity than the samples prefired at the other temperatures.