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Journal of Crystal Growth, Vol.523, 2019
Anisotropic growth of La2NiO4+delta: Influential pre-treatment in molten-flux synthesis
Molten-flux synthesis was applied to the mixed ionic-electronic conducting oxide La2NiO4+delta. Melt of NaOH was used to dissolve precursors, which were either coarse mixtures of the oxides La2O3 and NiO from a classical solid-state route or ultrafine mixtures of La2CO5 and NiO from a sol-gel process. To estimate optimum synthesis temperature for the sol-gel process, reaction sequence was monitored by in-situ X-ray diffraction. The molten-flux synthesis in ambient air was conducted at 400 degrees C for up to 14 h with variation of additional water content and the precursor stoichiometry. Purity and composition of products were investigated by ex-situ X-ray diffraction and wavelength dispersive X-ray spectroscopy. A maximum length of plate-like crystals of ca. 30 mu m in the a, b-plane was observed at a thickness of ca. 2 mu m in the c-axis (i.e. aspect ratio of 15). By varying several parameters of the molten-flux synthesis, both size and aspect ratio of La(2)NiO(4+delta )plate-like crystals could be varied over a wide range.