Chuanming Li

Investigation of Sm0.2Ce0.8O1.9/Na2CO3 nanocomposite 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.

Preparation of 2D α-Fe2O3 platelets via a hydrothermal heterogeneous growth approach and study of their magnetic properties

We report a novel strategy to modify the morphology of hydrothermal α-Fe2O3 particles via a heterogeneous growth process of BaFe12O19 crystal nuclei based on their structural similarity to α-Fe2O3 as well as their excellent crystallization habit to hexaplates. Various (001)-exposed single phase α-Fe2O3 platelets with diameters of 2.23–11.99 μm and thicknesses of 0.24–2.21 μm were successfully prepared without surfactants by using Fe(NO3)3·9H2O and Ba(NO3)2 as starting materials with NaOH as a precipitant in a facile hydrothermal process. The microstructural characterization by XRD, FESEM and EDS indicates that Ba2+ ions play an essential role in directing the formation of α-Fe2O3 platelets by producing BaFe12O19 nuclei as heterogeneous growth cores. This outcome has been supported by a series of experimental results, such as composition and cell parameter changes, morphology evolution, and the generation of double-layer α-Fe2O3 platelets. To facilitate the nucleation of BaFe12O19 while preventing its further growth, an appropriate NaOH concentration and barium-poor stoichiometry were required. Furthermore, the magnetic hysteresis measurements demonstrated that these 2D α-Fe2O3 platelets exhibit strong shape- and orientation-dependent magnetic properties.

Preparation of SDC–NC nanocomposite electrolytes with elevated densities: influence of prefiring and sintering treatments on their microstructures and electrical conductivities

Sm0.2Ce0.8O1.9–Na2CO3 (SDC–NC) nanocomposite powders and electrolytes were prepared through the precipitation of Sm-doped cerium/sodium complex carbonate and its prefiring and sintering operations. Their phase components and microstructures were characterized by XRD, FT-IR, TG-DSC, SEM and TEM, respectively, and, in particular, the sintering performance and oxide ionic and protonic conductivities of SDC–NC nanocomposite electrolytes prepared by prefiring and sintering at different temperatures were studied. It has been found that the SDC–NC nanocomposite powders derived from pre-firing treatments of non-crystalline carbonate precipitates are composed of SDC/NC nanocomposite core–shell structured particles. Moreover, the as-sintered SDC–NC nanocomposite electrolytes are generally made up of densely compacted SDC particles bound by NC phase, while their sintering performances and microstructures are significantly affected by the prefiring and sintering temperatures due to the differences in structural homogeneity and continuity of the NC phase. In addition, the oxide ionic and protonic conductivities of SDC–NC nanocomposite electrolytes can be strongly dependent upon the prefiring and sintering treatments, with the sample S-500-800 (prefired at 500 °C and sintered at 800 °C) showing the highest conductivities, 9.11 and 3.27 mS cm−1 at 600 °C in H2 and air, respectively. The single cell based on the electrolyte of S-500-800 showed an OCV of 0.99 V and a peak power density of 342 mW cm−2 at 550 °C. More interestingly, the dependence of electrical performance on the prefiring and sintering temperatures is discussed from the perspective of the significant effects of the prefiring and sintering treatments on the microstructures and interfacial interactions between the phases of disperse SDC nanoparticles and NC, which is homogeneously and continuously filled in between them.