H. Chiba

Ferromagnetism and large negative magnetoresistance in Bi1−xCaxMnO3 (x ≥ 0.8) perovskite

Abstract Polycrystalline perovskite manganites Bi 1−x Ca x MnO 3 (x ≥ 0.8) have been prepared by standard ceramic technique, and their magnetic and electronic property are examined down to 5 K. Ferromagnetic moment and reduced resistivity are observed for Bi 1−x Ca x MnO 3 (x ≥ 0.875), and also large negative magnetoresistances appear below T ′ c .

A New High-Pressure Phase of Bismuth Oxide

Abstract A new polymorphic form of bismuth oxide (Bi 2 O 3 ) is synthesized by a high-pressure technique (6 GPa and 880°C, and subsequently slow cooling). This phase can exist under ambient conditions, but it is fairly unstable. The crystal structure is determined to be the A-type rare-earth sesquioxide structure that is isotypic to La 2 O 3 . Hexagonal cell parameters are measured to be a = 3.878(1) A and c = 6.303(1) A. The pressure effect on a polarizable 6s2 lone pair character of Bi 3+ is discussed.

Synthesis and characterization of (Bi, AE)MnO3 (AE=Ca, Sr) system

Abstract The effects of electron lone pairs of trivalent bismuth ions on the crystal structure and magnetic properties were examined in Bi 1− x AE x MnO 3 (AE=Ca, Sr). Polycrystalline perovskite manganites Bi 1− x AE x MnO 3 were synthesized by using a conventional ceramic technique and a high-pressure technique (4 GPa). Perovskites with triclinic, monoclinic, and tetragonal distortions were found in Bi 1− x Sr x MnO 3 from X-ray powder diffraction. In particular superlattice reflections were found in BiMnO 3 by electron diffraction which revealed two kinds of unit cell, i.e. polymorphism. The bismuth lone pair character was reflected in these structures. Both Bi 1− x Ca x MnO 3 and La 1− x Ca x MnO 3 showed the same crystal symmetry and weak ferromagnetism in the Ca-rich region. However, the magnetic moment of Bi 1− x Ca x MnO 3 was larger than that of La 1− x Ca x MnO 3 with the same x value. Their ferromagnetism was suppressed by charge ordering with further substitution of trivalent cations, although the charge ordering temperature of the La-system is higher than that of the Bi system. The difference is probably associated with the Bi lone pair.

Growth of high-quality Bi 2 Sr 2 CaCu 2 O z crystal and characterization

We report growth of high-quality Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub z} single crystals with dimensions 2{times}1{times}0.03mm{sup 3} with a melt and growth technique. The composition of this crystal is homogeneous and very close to the stoichiometric composition. Structure characterization of single crystal was realized by measuring the (001) x-ray diffraction. The lattice parameters of a typical crystal are a=5.414(2){Angstrom}, b=5.413(2){Angstrom} and c=30.823(10){Angstrom}. The superconducting temperature T{sub c}=95 K with a sharp transition width (10{endash}90{percent} level) between 6 and 10 K was determined from resistivity and dc susceptibility. We have measured the magnetization of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub z} single crystal under magnetic field applied along the c-axis. The anomalous second peak effect appeared between 20{endash}30 K. We discuss the qualities of these crystals. {copyright} {ital 1997 Materials Research Society.}

Growth of high-quality Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub z} crystal and characterization

We report growth of high-quality Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub z} single crystals with dimensions 2{times}1{times}0.03mm{sup 3} with a melt and growth technique. The composition of this crystal is homogeneous and very close to the stoichiometric composition. Structure characterization of single crystal was realized by measuring the (001) x-ray diffraction. The lattice parameters of a typical crystal are a=5.414(2){Angstrom}, b=5.413(2){Angstrom} and c=30.823(10){Angstrom}. The superconducting temperature T{sub c}=95 K with a sharp transition width (10{endash}90{percent} level) between 6 and 10 K was determined from resistivity and dc susceptibility. We have measured the magnetization of Bi{sub 2}Sr{sub 2}CaCu{sub 2}O{sub z} single crystal under magnetic field applied along the c-axis. The anomalous second peak effect appeared between 20{endash}30 K. We discuss the qualities of these crystals. {copyright} {ital 1997 Materials Research Society.}

Synthesis and structure change of Ba1-xBixMnO3

Abstract Polycrystalline samples of Ba 1− x Bi x MnO 3 were synthesized over a wide Bi concentration range and examined by X-ray powder diffraction, electron diffraction and compositional analysis. The metal composition of the platelet-like crystals was Ba:Bi:Mn=47.8:2.3:49.9 for nominal composition x =0.05 and 0.1. A hexagonal shaped and platelet-like single crystal with the size of 160×150×15 μm 3 was obtained by a melt and growth technique using (Ba 0.9 Bi 0.1 )MnO 3 as precursor and Bi 2 O 3 as flux. The chemical composition of as-grown crystals was nearly the same as the bulk specimen. The relationship between the average ionic radius of the Ba/Bi cations in the A site and Bi content showed that the 9R phase was stabilized for x =0.05.

Growth and characterization of high-quality Bi2Sr2CaCu2Oz Crystal

Summary We report the growth of high-quality Bi 2 Sr 2 CaCu 2 O z single crystals with dimensions 2 × 1 × 0.03 mm 3 with a self-flux technique. The composition of these crystals is homogeneous and very close to the stoichiometric composition. Structure characterization of the single crystals was performed by measuring the (0 0 1) X-ray diffraction. The lattice parameters of a typical crystal are a = 0.5414(2) nm, b = 0.5413(2) nm and c = 3.0823(10) nm. The superconducting temperature T c = 95 K with a sharp transition width (10–90% level) between 2 and 3 K was determined from resistivity and DC susceptibility.