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Structural Analysis of Eu_2Mn_(2/3)Ta_ 4/3O_7 with a Pyrochlore-Related Structure

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Journal of Rare Earths 2004年第1期22卷 172-174页

作者：陈刚 Satoh Hirohisa kamegashira naoki Department of Applied Chemistry Department of Materials Science

Eu 2Mn 2/3Ta 4/3O 7 specimen was synthesized from Eu 2O 3, MnO and Ta 2O 5 in a reducing atmosphere. Structure analysis was carried out by Rietveld method from X-ray diffraction data. The X-ray diffraction profile calculated with monoclinic C2/c model was in a good agreement with the observed X-ray diffraction patterns since several small peaks of super lattice could be also assigned with C2/c symmetry in addition to fundamental reflection peaks. Eu 2Mn 2/3Ta 4/3O 7 has two kinds of distorted (Mn, Ta)O 6 octahedra and HTB layers, which deviates from the regular forms. Europium atoms coordinate to eight or seven oxygen atoms and lead to two kinds of polyhedra, EuO 8 and EuO 7 in this compound.

关键词： complex oxide structural analysis X-ray diffraction rare earths

Stability of phases in (Ba, Gd)MnO_3 solid solution system

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Journal of Rare Earths 2008年第2期26卷 233-236页

作者： Migaku Kobayashi Hidenori Tamura Hiromi Nakano Hirohisa Satoh naoki kamegashira Department of Chemistry and Biochemistry Numazu National College of Technology 3600 Ooka Numazu Electron Microscope Laboratory Ryukoku University Department of Materials Science Toyohashi University of Technology Tempaku-cho

The existing phases in BaxGd1-xMnO3 solid solution system （0≤x≤ 1） were studied by analyzing the detailed crystal structure of each composition from the results of the Rietveld method using powder X-ray diffraction data. For a small substitution of Ba for Gd （0≤x〈0. 1）, the orthorhombic phase with a perovskite type structure （Pnma space group） was stably formed and this fact was supported by the electron diffraction data. There existed an intermediate phase of Ba0.33Gd0.67MnO3, which was characterized as the tetragonal phase with perovskite structure. The composition range of this phase was narrow and almost line compound. Between the regions of these phases, there existed two-phase region. There was also a two-phase region between the intermediate tetragonal phase and BaMnO3. Measurement of electrical conductivities of these orthorhombic solid solutions and tetragonal phases showed semiconducting behaviors for both phases and the existence of the phase transition at high temperature for the orthorhombic phase, The transition temperature decreased as the Ba content increased.

关键词： rare earth manganite phase behavior X-ray diffractometry crystal structure electrical conductivity

Structural Analysis of a New Phase of BaNdMnO_4

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Journal of Rare Earths 2007年第S1期25卷 1-3页

作者： Hiromi Nakano Norikatsu Kawabata Hirohisa Satoh naoki kamegashira Ryukoku University SetaOtsu520-2194Japan Toyohasi University of Technology 441-8580Japan

Single crystal of BaNdMnO4 with I4/mmm was synthesized by a floating zone method. A new phase of BaNdMnO4 was obtained by annealing the single crystal in a reducing atmosphere at 573 K for 10 d. The structural change was analyzed by four-circle X-ray diffractometry and transmission electron microscopy. The new phase has an orthorhombic unit cell (Fmmm) of a=0.5486(2) nm, b=0.5484(2) nm, and c=1.3059(2) nm.

关键词： rare earth manganite structure transmission electron microscopy X-ray diffractometry

Phase Behavior and Crystal Structure of Perovskite-Type Rare Earth Complex Oxides

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Journal of Rare Earths 2006年第6期24卷 668-672页

作者： Migaku Kobayashi Ryoko Katsuraya Tsubasa Nara Yusuke Tomita Hiromi Nakano naoki kamegashira Department of Chemistry and Biochemistry Numazu College of Technology 3600 Ooka Numazu 410-8501 Japan Ryukoku University Seta Otsu 520-2194 Japan Department of Materials Science Toyohashi University of Technology Tempaku-cho Toyohashi 441-8580 Japan

Several compounds of rare earth complex oxides containing manganese and titanium were synthesized in Ar, and their crystal structures were analyzed by powder X-ray diffraction data and Rietveld method. Structures of A0.67Ln0.33 Mn0.33Ti0.6703（A = Ca or Sr and Ln = rare earth） were found to have orthorhombic symmetry with the space group Pnrna, and their interatomic distances and bond angles were obtained. This space group was also derived from electron microscopic study. Electrical conductivity of Cao.67Ln0.33Mn0.33Ti0.6703 for several rare earth elements showed a semiconducting property with the activation energy of 0.4 eV. Some of these compounds of the strontium system show the antiferromagnetic properties below 10 K.

关键词： perovskite crystal structure X-ray diffraction alkaline earth rare earth manganese titanium oxide