Towards the development of textured polycrystalline La₂NiO_4+δ membranes and their oxygen-transporting properties

Textured La₂NiO_4+δ membranes were fabricated by pressureless sintering in air using uniaxially pressed powder mixtures consisting of fine-grained equiaxial La₂NiO_4+δ matrix particles and plate-like La₂NiO_4+δ template particles in varying mass ratios. The template particles, obtained by molten-flux synthesis, were aligned perpendicular to the pressing direction. Subsequent sintering resulted in ceramic membranes with enhanced texturing along the crystallographic c-axis of La₂NiO_4+δ. X-ray diffraction patterns revealed a direct relationship: The higher the fraction of template particles in the ceramics, the more pronounced the c-axis texturing. The Lotgering orientation factor, calculated from the X-ray diffraction patterns, also demonstrated that an increasing proportion of the template particles in the ceramic materials led to stronger (00l) reflections. Additionally, the texturing degree in selected membranes was quantified by measuring pole figures. Scanning electron micrographs of the La₂NiO_4+δ samples with a small amount of template particles showed some individual plate-like grains well integrated into the matrix. Membrane porosity was observed to increase with higher quantities of template particles utilized. This was supported by measuring the membrane density using the Archimedes method: The larger the proportion of template particles in the ceramics, the lower the sample density. Besides, the presence of lanthanum, nickel, and oxygen in the membranes was confirmed by energy-dispersive X-ray spectroscopy. Finally, the effect of texturing on the oxygen permeation performance of the La₂NiO_4+δ membranes, in which the template particles are arranged along their c-axis, parallel to the oxygen flux direction, was investigated. The results indicated a reduction in oxygen flux as the level of c-axis texturing increased. Graphical abstract: (Figure presented.)