Tóthová Erika, Düvel André, Witte Ralf, Brand Richard A, Sarkar Abhishek, Kruk Robert, Senna Mamoru, Da Silva Klebson Lucenildo, Menzel Dirk, Girman Vladimír, Hegedüs Michal, Baláž Matej, Makreski Petre, Kubuki Shiro, Kaňuchová Mária, Valíček Jan, Hahn Horst, Šepelák Vladimír
Institute of Nanotechnology, Karlsruhe Institute of Technology, Eggenstein-Leopoldshafen, Germany.
Institute of Geotechnics, Slovak Academy of Sciences, Košice, Slovakia.
Front Chem. 2022 Mar 16;10:846910. doi: 10.3389/fchem.2022.846910. eCollection 2022.
Strontium ferromolybdate, SrFeMoO, is an important member of the family of double perovskites with the possible technological applications in the field of spintronics and solid oxide fuel cells. Its preparation a multi-step ceramic route or various wet chemistry-based routes is notoriously difficult. The present work demonstrates that SrFeMoO can be mechanosynthesized at ambient temperature in air directly from its precursors (SrO, α-Fe, MoO) in the form of nanostructured powders, without the need for solvents and/or calcination under controlled oxygen fugacity. The mechanically induced evolution of the SrFeMoO phase and the far-from-equilibrium structural state of the reaction product are systematically monitored with XRD and a variety of spectroscopic techniques including Raman spectroscopy, Fe Mössbauer spectroscopy, and X-ray photoelectron spectroscopy. The unique extensive oxidation of iron species (Fe → Fe) with simultaneous reduction of Mo cations (Mo → Mo), occuring during the mechanosynthesis of SrFeMoO, is attributed to the mechanically triggered formation of tiny metallic iron nanoparticles in superparamagnetic state with a large reaction surface and a high oxidation affinity, whose steady presence in the reaction mixture of the milled educts initiates/promotes the swift redox reaction. High-resolution transmission electron microscopy observations reveal that the mechanosynthesized SrFeMoO, even after its moderate thermal treatment at 923 K for 30 min in air, exhibits the nanostructured nature with the average particle size of 21(4) nm. At the short-range scale, the nanostructure of the as-prepared SrFeMoO is characterized by both, the strongly distorted geometry of the constituent FeO octahedra and the extraordinarily high degree of anti-site disorder. The degree of anti-site disorder = 0.5, derived independently from the present experimental XRD, Mössbauer, and SQUID magnetization data, corresponds to the completely random distribution of Fe and Mo cations over the sites of octahedral coordination provided by the double perovskite structure. Moreover, the fully anti-site disordered SrFeMoO nanoparticles exhibit superparamagnetism with the blocking temperature = 240 K and the deteriorated effective magnetic moment = 0.055 per formula unit.
钼酸锶铁（SrFeMoO）是双钙钛矿家族的重要成员，在自旋电子学和固体氧化物燃料电池领域可能具有技术应用价值。其制备过程，无论是多步陶瓷路线还是各种基于湿化学的路线，都非常困难。目前的工作表明，SrFeMoO可以在室温空气中通过机械合成直接从其前驱体（SrO、α-Fe、MoO）以纳米结构粉末的形式制备出来，无需溶剂和/或在可控氧逸度下进行煅烧。利用X射线衍射（XRD）以及包括拉曼光谱、铁穆斯堡尔光谱和X射线光电子能谱在内的多种光谱技术，系统地监测了SrFeMoO相的机械诱导演化以及反应产物的远离平衡结构状态。在SrFeMoO的机械合成过程中发生的铁物种（Fe→Fe）独特的广泛氧化以及钼阳离子（Mo→Mo）的同时还原，归因于机械触发形成具有大反应表面和高氧化亲和力的超顺磁态微小金属铁纳米颗粒，其在研磨反应物的反应混合物中的稳定存在引发/促进了快速的氧化还原反应。高分辨率透射电子显微镜观察表明，即使在空气中923 K下进行30分钟的适度热处理后，机械合成的SrFeMoO仍呈现纳米结构性质，平均粒径为21(4)nm。在短程尺度上，制备的SrFeMoO的纳米结构的特征在于，组成的FeO八面体的几何形状严重扭曲以及反位无序程度极高。通过当前的实验XRD、穆斯堡尔和超导量子干涉仪（SQUID）磁化数据独立得出的反位无序度 = 0.5，对应于双钙钛矿结构提供的八面体配位位点上Fe和Mo阳离子的完全随机分布。此外，完全反位无序的SrFeMoO纳米颗粒表现出超顺磁性，其阻塞温度 = 240 K，有效磁矩恶化至每公式单位 = 0.055 。
