Abstract α-NaFeO2 type layered oxides shows reversible intercalation/de-intercalation of sodium ions between the oxide layers, which is suitable as regenerable CO2 absorber and cathode material for secondary batteries. This paper reports a critical effect of heating atmosphere to synthesize pure α-NaFeO2 from equimolar sodium nitrate and iron oxide. Reaction of NaNO3 with γ-Fe2O3 was much faster in nitrogen than oxygen atmosphere and high-purity α-NaFeO2 was yielded in a few hours of heat treatment in nitrogen while in oxygen atmosphere the reaction was sluggish, resulting in partially sodiated γ-Fe2O3. Inert atmosphere thermodynamically enhances nitrate decomposition, which controls the reaction rate of NaNO3 with γ-Fe2O3, and increases the solubility of γ-Fe2O3 in molten NaNO3 to promote topotactic phase transformation to α-NaFeO2. Molten NaNO3 works as a solvent for ferric ions and a redox buffer for maintaining the lattice oxygen structure and oxidation state of γ-Fe2O3. Larger iron oxide crystal was found to be suitable for production of high-purity α-NaFeO2 in a wide temperature range.

中文翻译：

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硝酸钠和热处理气氛对α-NaFeO2层状氧化物合成的影响

摘要 α-NaFeO2 型层状氧化物在氧化物层之间表现出可逆的钠离子嵌入/脱嵌，适合作为可再生的 CO2 吸收剂和二次电池的正极材料。本文报道了加热气氛对从等摩尔硝酸钠和氧化铁合成纯 α-NaFeO2 的关键影响。NaNO3 与 γ-Fe2O3 在氮气中的反应速度比氧气气氛中快得多，在氮气中热处理数小时即可得到高纯度的 α-NaFeO2，而在氧气气氛中反应缓慢，导致部分钠化的 γ-Fe2O3。惰性气氛在热力学上促进了硝酸盐的分解，从而控制了 NaNO3 与 γ-Fe2O3 的反应速率，并增加了 γ-Fe2O3 在熔融 NaNO3 中的溶解度，从而促进了向 α-NaFeO2 的拓扑相变。熔融的 NaNO3 作为三价铁离子的溶剂和氧化还原缓冲剂，用于维持 γ-Fe2O3 的晶格氧结构和氧化态。发现较大的氧化铁晶体适合在较宽的温度范围内生产高纯度 α-NaFeO2。