Compounds of nominal composition NaLa₄Mo₃O₁₅F_1−xCl_x (x = 0–0.7) have been obtained for the first time as ceramics and single crystals. All the compounds belong to the cubic crystal system and are isostructural to undoped crystals of the Ln₅Mo₃O₁₆ family (Ln = La–Gd). A study of the physical properties of the obtained phases has shown their significant change compared to undoped compounds and a reversible jump in conductivity near 600 °C. According to X-ray diffraction analysis, sodium atoms are localized near the positions of rare-earth cations La2, and halogen impurities enter partially occupied general positions of O2 atoms and the interstices formed by six La1 atoms. As the temperature increases, chlorine ions leave O2 positions and interstices. This increases the number of vacancies and creates new ion transport pathways. A jump in conductivity occurs when three conditions are simultaneously met: an increase in the number of vacancies, the appearance of new charge transport pathways, and, possibly, an increase in the mobility of the main charge carriers, oxygen ions, due to electrostatic repulsion between anions (O²⁻, F⁻, Cl⁻).

中文翻译：

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含钠和含卤素的类萤石稀土钼酸盐的结构特征


标称组成 NaLa₄Mo₃O₁₅F_1−xCl_x （x = 0–0.7） 的化合物首次以陶瓷和单晶形式获得。所有化合物都属于立方晶系，与 Ln₅Mo₃O₁₆ 族 （Ln = La-Gd） 的未掺杂晶体同构。对所得相的物理性质的研究表明，与未掺杂的化合物相比，它们发生了显著变化，并且在 600 °C 附近电导率发生了可逆跳跃。 根据 X 射线衍射分析，钠原子位于稀土阳离子 La2 的位置附近，卤素杂质进入 O2 原子部分占据的一般位置和由 6 个 La1 原子形成的空隙。随着温度的升高，氯离子离开 O2 位置和空隙。这增加了空缺数量并创造了新的离子传输途径。当同时满足三个条件时，就会发生电导率的跳跃：空位数量的增加，新的电荷传输路径的出现，以及由于阴离子之间的静电排斥（O^2-、F^--、Cl^-）可能增加主要电荷载流子氧离子的迁移率。