A. K. Koryttseva, A. V. Knyazev, E. V. Syrov, D. G. Fukina, I. A. Bazhenova, V. V. Cheverikin, S. V. Kuzovchikov
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The phases that are isostructural to the mineral langbeinite (K<sub>2</sub>Mg<sub>2</sub>(SO<sub>4</sub>)<sub>3</sub>, sp. gr. <i>P</i>2<sub>1</sub>3) crystallize in the range of 0 ≤ <i>x</i> ≤ 0.4, while the phases isostructural to NASICON NaZr<sub>2</sub>(PO<sub>4</sub>)<sub>3</sub> (sp. gr. <i>R</i>3-<i>c</i>) crystallize in the range of 0.9 ≤ <i>x</i> ≤ 1. The standard enthalpies of formation were determined by high-temperature drop-solution calorimetry in molten sodium molybdate solvent (3Na<sub>2</sub>O⋅4MoO<sub>3</sub>) at 800°C using an isoperibolic differential calorimeter of the Tian–Calvet type. The behavior of the obtained energy characteristics is discussed in accordance with the structural evolutions in the given range of solid solution compositions. This study expands the knowledge about the isomorphism of alkali cations in framework structures, showing the ways of possible changes in the properties in the given series.</p>","PeriodicalId":767,"journal":{"name":"Russian Journal of Physical Chemistry A","volume":"99 9","pages":"1985 - 1998"},"PeriodicalIF":0.8000,"publicationDate":"2025-09-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"https://link.springer.com/content/pdf/10.1134/S0036024425701432.pdf","citationCount":"0","resultStr":"{\"title\":\"Thermochemical and Structural Properties of K2–2xNa2xFe1.5Nb0.5(PO4)3 (0 ≤ x ≤ 1) Solid Solutions with NASICON and Langbeinite Structures\",\"authors\":\"A. K. Koryttseva, A. V. Knyazev, E. V. Syrov, D. G. Fukina, I. A. Bazhenova, V. V. Cheverikin, S. V. 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引用次数: 0
摘要
对K \(_{{2 - 2x}}\) Na2xFe1.5Nb0.5(PO4)3（0≤x≤1）固溶体进行了研究，确定了NASICON和朗贝石结构类型的存在边界，并确定了混合能量学。研究对象可以用作钠离子电池的阴极。粉末样品采用固相法制备，采用x射线显微分析、x射线衍射和差示扫描量热法进行表征。利用室温下的x射线粉末衍射数据，用Rietveld法对结构进行了细化。与langbeinite矿（K2Mg2(SO4)3, sp. gr. P213）相同构在0≤x≤0.4范围内结晶，与NASICON NaZr2(PO4)3 （sp. gr. R3-c）相同构在0.9≤x≤1范围内结晶。在熔融钼酸钠溶剂（3Na2O·4MoO3）中，采用高温滴液量热法在800℃下测定了标准生成焓，采用Tian-Calvet型等循环差量热计。根据给定的固溶体组成范围内的结构演变，讨论了所得能量特性的行为。本研究拓展了对框架结构中碱阳离子同构性的认识，揭示了给定系列中碱阳离子性质可能发生变化的途径。
Thermochemical and Structural Properties of K2–2xNa2xFe1.5Nb0.5(PO4)3 (0 ≤ x ≤ 1) Solid Solutions with NASICON and Langbeinite Structures
The K\(_{{2 - 2x}}\)Na2xFe1.5Nb0.5(PO4)3 (0 ≤ x ≤ 1) solid solutions were studied to find the boundaries of existence of the NASICON and langbeinite structural types and to determine the mixing energetics. The objects of study can find use as cathodes for Na-ion batteries. The powder samples were obtained by the solid-phase method and characterized by X-ray spectral microanalysis, X-ray diffraction, and differential scanning calorimetry. The structure was refined by the Rietveld method using X-ray powder diffraction data at room temperature. The phases that are isostructural to the mineral langbeinite (K2Mg2(SO4)3, sp. gr. P213) crystallize in the range of 0 ≤ x ≤ 0.4, while the phases isostructural to NASICON NaZr2(PO4)3 (sp. gr. R3-c) crystallize in the range of 0.9 ≤ x ≤ 1. The standard enthalpies of formation were determined by high-temperature drop-solution calorimetry in molten sodium molybdate solvent (3Na2O⋅4MoO3) at 800°C using an isoperibolic differential calorimeter of the Tian–Calvet type. The behavior of the obtained energy characteristics is discussed in accordance with the structural evolutions in the given range of solid solution compositions. This study expands the knowledge about the isomorphism of alkali cations in framework structures, showing the ways of possible changes in the properties in the given series.
期刊介绍：
Russian Journal of Physical Chemistry A. Focus on Chemistry (Zhurnal Fizicheskoi Khimii), founded in 1930, offers a comprehensive review of theoretical and experimental research from the Russian Academy of Sciences, leading research and academic centers from Russia and from all over the world.
Articles are devoted to chemical thermodynamics and thermochemistry, biophysical chemistry, photochemistry and magnetochemistry, materials structure, quantum chemistry, physical chemistry of nanomaterials and solutions, surface phenomena and adsorption, and methods and techniques of physicochemical studies.
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