Melilite-type gallates of general formula RE_1+xAE_1–xGa₃O_7+x/2 are of interest for their ability to host mobile interstitial oxide ions in [Ga₃O_7+x] layers. The crystal structure of Ca₅Ga₆O₁₄ is closely related to melilite, with [Ga₃O₇] layers stacked in a more complex way to accommodate an additional 0.5 interlayer cations per formula unit, suggesting the potential for similar oxide ion conduction behavior. We used a computational approach to identify the most promising routes to interstitial oxide incorporation into Ca₅Ga₆O₁₄, leading to an experimental investigation of the system Ca_5–xLa_xGa₆O_14+x/2. Single-phase materials were obtained in the range 0 ≤ x ≤ 0.25 by solid state reactions, producing an ∼40× increase in ionic conductivity at 800 °C. This limited compositional range presents a challenge for characterization of the charge-compensating defects. The La substituents were observed directly by X-ray diffraction and STEM–EDX, and a combination of different structural characterization techniques and DFT calculations indicated the presence of interstitial oxide ions indirectly, explaining the conductivity response. As higher carrier concentrations (x > 0.25) are apparently inaccessible in this system, we conclude that its potential as a useful oxide ion conductor is more limited than that of established melilite materials such as La_1+xCa_1–xGa₃O_7+x/2.

中文翻译：

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La 替换为黄长石衍生物 Ca5Ga6O14：预测、合成和离子电导率


通式为 RE _{1+ x} AE _{1– x} Ga ₃ O _{7+ x /2}的黄长石型镓酸盐因其在 [Ga ₃ O _{7+ x} ] 层中容纳移动间隙氧化物离子的能力而受到关注。 Ca ₅ Ga ₆ O ₁₄的晶体结构与黄长石密切相关，[Ga ₃ O ₇ ]层以更复杂的方式堆叠，每个分子式单元可容纳额外的0.5个层间阳离子，这表明具有类似氧化物离子传导行为的潜力。我们使用计算方法来确定将间隙氧化物掺入 Ca ₅ Ga ₆ O _{14 的}最有希望的途径，从而对 Ca _{5– x} La _x Ga ₆ O _{14+ x /2}系统进行了实验研究。通过固相反应获得了 0 ≤ x ≤ 0.25 范围内的单相材料，在 800 °C 下离子电导率增加了约 40 倍。这种有限的成分范围对电荷补偿缺陷的表征提出了挑战。通过 X 射线衍射和 STEM-EDX 直接观察到 La 取代基，结合不同的结构表征技术和 DFT 计算间接表明间隙氧化物离子的存在，从而解释了电导率响应。随着载流子浓度升高 ( x > 0.25）在该系统中显然无法获得，我们得出结论，其作为有用的氧化物离子导体的潜力比现有的黄长石材料（例如La _{1+ x} Ca _{1– x} Ga ₃ O _{7+ x /2 ）}更有限。