Tōru Ishigaki

Rietveld Refinement of the Structure of Ba2YCu3O7-x with Neutron Powder Diffraction Data

The crystal structure of a high Tc superconductor, Ba2YCu3O7-x, has been refined by the Rietveld analysis of TOF neutron powder diffraction data. Two polymorphs of Ba2YCu3O7-x are contained in the sample: orthorhombic (74%) and tetragonal (26%) forms. The two forms have nearly the same structure closely related to that of perovskite-type compounds. In the orthorhombic form, the occupation factor of an oxygen atom on the a axis differed greatly from that on the b axis, which is the main reason why Ba2YCu3O7-x crystallizes in the orthorhombic form.

X-Ray Diffraction Study on the Crystal Structure of Nd1+xBa2-xCu3O7-δ

Crystal structures in the Nd1+xBa2-xCu3O7-δ system have been investigated by X-ray powder diffraction combined with Rietveld analysis. The compound NdBa2Cu3O7-δ is isomorphic with orthorhombic YBa2Cu3O7-δ. With the increase of x the orthorhombic distortion decreases, and the compound becomes tetragonal at x=0.2. The tetragonal structure is isomorphic with the tetragonal form of YBa2Cu3O7-δ. Tc of the compounds with x=0 and 0.05 is above 90 K, which decreases monotonically with x and the compound becomes semiconducting at x=0.4.

The crystal structure of the superconducting copper oxide carbonate (Ba1−xSrx)2Cu1+yO2+2y+z(CO3)1−y: Defects in charge reservoirs and superconductivity

Abstract The crystal structure of a new superconductor in the Ba-Sr-Cu-C-O system has been determined by neutron powder diffraction with the auxiliary use of electron diffraction and high-resolution transmission electron microscopy. This compound is a member of a solid solution with the general formula (Ba1-xSrx)2Cu1+yO2+2y+zCO3)1-y, where x=4/9 , y=1/9, and z=0.10. It is tetragonal with a space group P4212 or P 4 21m and lattice parameters of a=5.56405 (18) A and c=7.8570(4) A . It is closely related in structure to Sr2CuO2CO3, which is an end member of the solid solution: x=1, y=0, and x=0. Two-dimensional CuO2 sheets and carbonate slabs, (Ba1-xSrs)2CuyO2y+z(CO3)1-y, alternate with each other along the [001] directions. As the formula of the slab shows, about 11% of C atoms are substituted by excess Cu atoms coordinated to O atoms which amount to 2y+z in the formula unit. These substitutional and interstitial defects enable hole carriers to move from the carbonate slab to the CuO2 conduction sheet.

Crystal Structure of a Ba-Y-Cu-O Superconductor as Revealed by Rietveld Analysis of X-Ray Powder Diffraction Data

The crystal structure of a Ba-Y-Cu-O superconductor was refined by the Rietveld analysis of X-ray powder diffraction data. This material is orthorhombic with lattice parameters a = 3.8845 A, b = 3.8293 A, and c = 11.6926 A. Possible space groups are P222, Pmm2, and Pmmm. Metal atoms have essentially the same configuration as that in the perovskite-type structure. A structural model is proposed in which an oxygen atom at (0, 0, 1/2) is deficient.

Crystal Structure of the Orthorhombic Form of Ba2YCu3O7-x at 42 K

The crystal structure of the low-temperature form of Ba2YCu3O7-x at 42 K was refined by the Rietveld analysis of TOF neutron powder diffraction data. This material is orthorhombic with space group Pmmm and lattice constants a=3.8800 A, b=3.8122 A, and c=11.6264 A. It has an oxygen-deficient triperovskite structure in which oxygen atomson a z=1/2 plane are lacking completely, two oxygen sites on a z=0 plane are partially occupied, and Ba2+ and Y3+ ions are ordered in a [Ba-Y-Ba]∞ sequence along the c axis. The occupation factors of oxygen at (1/2, 0, 0) and (0, 1/2, 0) are 0.84 and 0.05, respectively.

A Revised Structural Model for the Ba-Y-Cu-O Superconductor

A possible structure with a space group Pmmm is proposed for a superconducting oxide, Ba2YCu2O7, on the basis of Rietveld analysis of X-ray powder diffraction data. It has a metal-ordered, layered structure in which an oxygen atom at a 1c site is deficient completely, and 1b and 1e sites are partially occupied. Each layer consists of those pyramids and octahedra of oxygen atoms which are linked with each other by sharing corners.

Crystal Structure of the Tetragonal Form of Ba2YCu3O7-x

The crystal structure of the high-temperature form of Ba2YCu3O7-x was refined by the Rietveld analysis of TOF neutron powder diffraction data taken at 49 K. This compound is tetragonal with lattice constants a = 3.8533 A and c = 11.7631 A. It has an oxygen-deficient triperovskite structure, in which oxygen atoms on a z = 1/2 plane are missing, an oxygen site at (0, 1/2, 0) is about 9% occupied, and Ba2+ and Y3+ ions are completely ordered in a [Ba-Y-Ba]∞, sequence along the c axis.

Rietveld analysis of the composite crystal in superconducting Bi2+xSr2−xCuO6+y

Abstract The modulated crystals of Bi-based superconducting oxides are well described as composite crystals [Walker and Que, Phys. Rev. B 45 (1992) 14]. The structure of the superconducting oxide Bi 2+ x Sr 2− x CuO 6+ y was analyzed for the first time as composite crystal by the Rietveld method with the combined use of X-ray and TOF neutron diffraction data. It consists of two interpenetrating one-dimensionally modulated structures with the superspace groups N B2/b 1 1 and P I2/m 1 s . The analysis revealed large atomic displacements from average positions in the Bi-O, Sr-O, Cu-O layers. The oxygen arrangement in the Bi-O layer is similar to this in Bi 2+ x (Sr, Ca) 3− x Cu 2 O 8+ y .

Crystal Structure of the Superconductor Ba1.8Nd1.2Cu3O7-y

The structure parameters of a superconductor with the nominal composition Ba1.8Nd1.2Cu3O7-y were refined by the Rietveld analysis of TOF neutron powder diffraction data. This material is tetragonal with lattice constants a=3.8919 A and c=11.6811 A and isomorphous with Ba1.5La1.5Cu3O7±y with an oxygen-deficient triperovskite structure. An oxygen site at (0, 1/2, 0) is 49% occupied, the Nd3+ ion at (1/2, 1/2, 1/2) is coordinated to eight oxide ions, and a metal site at (1/2, 1/2, 0.1842) is 90% and 10% occupied by Ba2+ and Nd3+ ions, respectively.

Crystal Structure of the High Tc Superconductor LnBa2Cu3O7-δ (Ln=Sm, Eu and Gd)

The crystal structure of the high Tc superconductor LnBa2Cu3O7-δ (Ln=Sm, Eu and Gd) has been determined by Rietveld analysis of X-ray powder diffraction data. The compounds crystallize in an oxygen-deficient layered perovskite structure with space group Pmmm. The structure is isomorphic with YBa2Cu3O7-δ. The Ln and Ba atoms have an ordered arrangement, oxygen on a z=1/2 plane is missing and the oxygen site on the basal Cu plane is selectively occupied.