Hydrothermal Synthesis, Crystal Structure, and Superconductivity of a Double-Perovskite Bi Oxide

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• 作者：Mirza H. K. Rubel ; Takahiro Takei ; Nobuhiro Kumada ; M. Mozahar Ali ; Akira Miura ; Kiyoharu Tadanaga ; Kengo Oka ; Masaki Azuma ; Masatomo Yashima ; Kotaro Fujii ; Eisuke Magome ; Chikako Moriyoshi ; Yoshihiro Kuroiwa ; James R. Hester ; Maxim Avdeev
• 刊名：Chemistry of Materials
• 出版年：2016
• 出版时间：January 26, 2016
• 年：2016
• 卷：28
• 期：2
• 页码：459-465
• 全文大小：400K
• ISSN：1520-5002

文摘

Double-perovskite Bi oxides are a new series of superconducting materials, and their crystal structure and superconducting properties are under investigation. In this paper, we describe the synthesis and characterization of a new double-perovskite material that has an increased superconductive transition temperature of 31.5 K. The structure of the material was examined using powder neutron diffraction (ND), synchrotron X-ray diffraction (SXRD), and transmission electron microscopy (TEM). Rietveld refinement of the sample based on ND and SXRD data confirmed an A-site-ordered (K_1.00)(Ba_1.00)₃(Bi_0.89Na_0.11)₄O₁₂ double-perovskite-type structure with the space group Im3?m (No. 229). This structural analysis revealed the incorporation of Na with Bi in the structure and a bent bond between (Na, Bi)–O–(Na, Bi). TEM analyses also confirmed a cubic double-perovskite structure. This hydrothermally synthesized compound exhibited a large shielding volume fraction, exceeding 100%, with onset of superconductivity at ～31.5 K. Its electrical resistivity dropped near onset at ～28 K, and zero resistivity was confirmed below 13 K. The calculated band structure revealed that the metallicity of the compound and the flatness of the conduction bands near the Fermi level (E_F) are important for the appearance of superconductivity.