New Oxide-Ion Conductor SrYbInO₄ with Partially Cation-Disordered CaFe₂O₄‑Type Structure

In the present work, we have discovered a new oxide-ion conductor SrYbInO₄ with CaFe₂O₄-type structure. SrYbInO₄ is the first example of CaFe₂O₄-type pure oxide-ion conductors where the oxide-ion conduction is dominant. It was found that the activation energy for the oxide-ion conduction of SrYbInO₄ of 1.76(13) eV is lower than that of a mixed conductor CaFe₂O₄ of 3.3 eV. Rietveld analysis of neutron and synchrotron X-ray diffraction data and density functional theory (DFT)-based calculations revealed that the crystal structure of the new material SrYbInO₄ consists of Sr and two types of double octahedra, <i>B</i>₂O₁₀ and <i>C</i>₂O₁₀. Here, <i>B</i> and <i>C</i> are Yb_0.574(2)In_0.426(2) and In_0.574(2)Yb_0.426(2), respectively, which indicates partial Yb/In occupational disorder. Both <i>B</i>₂O₁₀ and <i>C</i>₂O₁₀ double octahedra form infinite columns along the <i>b</i> axis. The bond valence-based energy landscape of an O^2– test ion indicates one-dimensional diffusion of oxide ions along the edges of double octahedra in the <i>b</i> direction

Coordination Site Disorder in Spinel-Type LiMnTiO₄

LiMnTiO₄ was prepared through solid-state syntheses employing different heating and cooling regimes. Synchrotron X-ray and neutron powder diffraction data found quenched LiMnTiO₄ to form as single phase disordered spinel (space group <i>Fd</i>3̅<i>m</i>), whereas slowly cooled LiMnTiO₄ underwent partial phase transition from <i>Fd</i>3̅<i>m</i> to <i>P</i>4₃32. The phase behavior of quenched and slowly cooled LiMnTiO₄ was confirmed through variable-temperature synchrotron X-ray and neutron powder diffraction measurements. The distribution of Li between tetrahedral and octahedral sites was determined from diffraction data. Analysis of the Mn/Ti distribution in addition required Mn and Ti K-edge X-ray absorption near-edge structure spectra. These revealed the presence of Mn³⁺ in primarily octahedral and Ti⁴⁺ in octahedral and tetrahedral environments, with very slight variations depending on the synthesis conditions. Magnetic measurements indicated the dominance of antiferromagnetic interactions in both the slowly cooled and quenched samples below 4.5 K

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

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 <i>Im</i>3̅<i>m</i> (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 (<i>E</i>_F) are important for the appearance of superconductivity