Effects of Sr substitution in La 2−x Sr x NiO 4+δ (x = 0.2, 0.4, 0.6, and 0.8) on the oxygen stoichiometry, phase and transport properties were studied. Mixed effects between reduction of oxygen excess and increasing valence of Ni were found as charge compensation mechanisms. Highest oxygen diffusivity found at the minimum Sr substitution x=0.2 with an unusual increase observed when the x = 0.8. ARTICLE This journal isStoichiometry and oxygen diffusion properties of La 2−x Sr x NiO 4±δ with x = 0.2, 0.4, 0.6, and 0.8 prepared via a sol-gel method were investigated in this study. Iodometric titration and thermogravimetric analysis were used to determine the oxygen non-stoichiometry. Over the entire compositional range, the samples exhibit oxygen hyperstoichiometry with the minimum value δ = 0.14 at x = 0.4. Mixed effects between reduction of oxygen excess and increasing valence of Ni were found as charge compensation mechanisms; the former dominated at a low level of substitution, x < 0.4, while the latter dominated at higher levels of Sr (0.4 < x < 0.8). The highest oxygen diffusion coefficient was found for the minimum amount of Sr substitution, x = 0.2, continuously decreasing with x until x = 0.6. An unusual increase in D* was observed when the Sr content increased up to x = 0.8.

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In this study, sol–gel synthesis conditions for the formation of La2−xSrxNiO4 ( x=0 , 0.2, 0.4, 0.6, and 0.8) compounds were investigated. Effects of Sr substitution on A-site on the properties of the compounds were studied using Fourier transform IR spectroscopy, X-ray diffractometry, scanning electron microscopy, and electrical and thermal analyses. A simple sol–gel preparation process was successfully developed at room temperature using water as the solvent in the presence of ethanolamine as the directing agent. The sol–gel synthesis method was effective in yielding higher purity and more homogenous samples than those synthesized via the solid-state reaction method. The addition of Sr helped stabilize the Ruddlesden–Popper structure, and a highly agglomerated morphology of the sintered samples with Sr substitution was observed, resulting in lower density. Sr helped increase conductivity, whereas its effect on thermal expansion was not as pronounced. La1.2Sr0.8NiO4 synthesized via the sol–gel process provided a conductivity of 160 S/cm at 500°C with a coefficient of thermal expansion value of 13×10−6°normalC−1 between 400 and 700°C .

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