Hydrazine-nitrate combustion synthesis of BaCeO3 preceramic powders: structure, morphology and thermophysical properties

In the present work, preceramic nanocrystallite barium cerate (BaCeO3) was successfully synthesized using the hydrazine-nitrate combustion method. Using carbon-free hydrazine (N2H4) as fuel significantly reduced the formation of carbon by-products. Characterization of the as-received powders was performed by XRD, energy-dispersive X-ray spectroscopy (EDXS), scanning electron microscopy (SEM), simultaneous thermal analysis (DTA-TGA) and adsorption-structural analysis (N2, 77 K). Thermophysical properties of the sample annealed at 1000 °С were investigated using laser flash analysis (LFA) in the temperature interval of 1000 °С. As a result of a comprehensive study, the sequence of chemical and phase transformations that lead to the formation of BaCeO3 with a rhombic structure (Pnma, a = 6.2145 Å, b = 8.7776 Å, c = 6.2337 Å) during the thermal processing of combustion products was investigated. It was established that the average size of the obtained nanocrystals is 38 ± 3 nm and that they form micron-sized agglomerates with a specific surface area of the powder of 4.8 m2/g. It was shown that the sintered sample of BaCeO3 is characterized by thermal diffusivity values of 0.28 to 0.20 mm2/s and thermal conductivity values of 0.41 to 0.35 W/mK, depending on temperature. These results, given the impact of porosity on the sample (~ 40%), show very good agreement with the thermophysical characteristics of densely sintered ceramics based on BaCeO3 – a solid oxide electrolyte SOFC. Consequently, the proposed method of hydrazine-nitrate synthesis of BaCeO3 presents itself as a promising approach to obtaining preceramic powders and ceramics in the area of SOFC.