N. Ohnishi

The crystal structure of (C0.4Cu0.6)Sr2(Y0.86Sr0.14)Cu2O7

Abstract The crystal structure of a new compound, (C0.4Cu0.6)Sr2(Y0.86Sr0.14)Cu2O7, is derived from the structure of YBa2Cu3O7. Forty percent of CuO chains in the YBa2Cu3O7 structure are replaced by CO3 groups. This new compound has a superstructure along the a-axis and the c-axis. Diffuse superlattice reflections having periods of a∗/2-a∗/3 and c∗/2 were observed in electron diffraction patterns. Locally ordered distributions of C and Cu atoms were seen high-resolution images taken by transmission electron microscopy with an incident beam parallel to [010]. The basic structure of this superstructure was determined by neutron powder diffraction, assuming orthorhombic symmetry with the space group, Pmmm (lattice constants: a=3.8278(2), b=3.8506(2) and c=11.1854(5) A ).

Structure analysis of oxygen-deficient TlSr2CuOy by neutron diffraction and high-resolution electron microscopy

Abstract The crystal structure of orthorhombic TlSr 2 CuO y was determined by Rietveld analysis of neutron powder diffraction data with the aid of electron diffraction and high-resolution electron microscopy. We found that oxygen vacancies are formed along the a -direction in a CuO 2− z sheet, which is consistent with a superstructure of twice the subcell along the b -direction. CuO 6 octahedra and CuO 4 square planes alternate along the b -direction by sharing their corners in accordance with the ordered oxygen vacancies in the CuO 2− z sheet. An apical oxygen atom in the CuO 6 octahedron is nearer to a TlO layer than an oxygen atom shared by a TlO 6 octahedron and the CuO 4 plane. A crystal-structure image obtained by high-resolution electron microscopy could be successfully reproduced by computer simulation using structure parameters obtained by neutron powder diffraction.

Structure of Ba2InCuOy: A new layered cuprate with a blocking layer of BaInOy perovskite

Abstract A new blocking layer with an a -axis length of 4.18 A, BaInO y , was found. The blocking layer supplies an apical oxygen to the CuO 2 layer and produces an oxygen vacancy in the in-plane of the CuO 2 layer. By matching the blocking layer with the CuO 2 layer, a new layered cuprate, Ba 2 InCuO 4.53 , was prepared. Its space group was Pmmm with lattice parameters of a=4.1820(6) A , b=4.1820(5) A and c=8.0889(9) A . The fact that the a - and b -axis lengths of Ba 2 InCuO 4.53 compound are much longer than those of the other cuprate compounds is explained by the existence of an oxygen vacancy in the CuO 2 layer. Its resistivity at room temperature was as large as 28.8 MΩcm. The insulating property probably comes from the existence of the oxygen vacancy in the CuO 2 layer.

Hexagonal-orthorhombic phase transformation of AlPO4-5 aluminophosphate molecular sieve

Abstract AlPO 4 -5 crystals with an orthorhombic structure were obtained by using a synthesis medium containing fluoride anions and tropine as a template. Powder X-ray diffraction pattern of the as-synthesized crystals was indexed by the space group Ccc2 with a = 13.78 A, b = 23.33 A and c = 8.44 A. The orthorhombic phase showed a reversible transformation into a hexagonal form around 400 K.

Zeolites and related materials studied by electron microscopy

Abstract Four areas of zeolite research have recently advanced. The first area is the characterization of the fine structure of zeolites. The second area is the determination of new framework structures. The third is the characterization of materials within confined spaces and the fourth is the development of new techniques for studying zeolites and related materials.

Structural and superconducting properties of iodine-intercalated Bi2Sr2Ca1−xYxCu2Oz

Abstract The structual and superconducting properties of Bi 2 Sr 2 Ca 1− x Y x Cu 2 O z intercalated with iodine between the Bi-O bila yers were studied. Formation of the stage-1 compound was verified by X-ray analysis, TG analysis and TEM observation. Expansion of the c -axis, which is caused by increase in the distance of the BiO-BiO layers, decreases with decreasing intercalated iodine concentration down to 60%. The expansion of the c -axis of fully intercalated compounds increases with increasing Y content from 7.2 A for x =0 to 7.5 A for x =1.0. The temperature dependence of resistivity showed that iodine-doped samples ( x =0 and 0.4) were more semiconductive than non-doped samples. The T c of the IBi 2 Sr 2 Ca 1− x Y x Cu 2 O z series in the over-doped region was reduced by 2–10 K compared with non-intercalated samples.

Synthesis and superconductivity of oxycarbonates of the Tl-1201 phase

Abstract TlBa x Sr 4- x Cu 2 (CO 3 )O y oxycarbonates with the Tl-1201 structure were synthesized over a wide range of x (1.0≤ x ≤3.2) and examined by X-ray powder diffraction, electron diffraction, high-resolution electron microscopy and magnetometry methods. New phases with the Tl-1201 structure having 6 and 7 times periodicities along the b -axis were isolated. The former was stable for a wide Ba-rich range (1.8≤ x ≤3.2), and the latter was observed for a smaller Ba content range (1.2≤ x ≤1.6). The phase stability was found to depend on the synthesis condition. The maximum T c of the as-synthesized specimen in this series occurred at about 70 K around x =2.0. The Meissner volume fraction of the as-synthesized specimen ( x =2.4) was 30% at 5 K.

Ordered arrangement of carbon and copper atoms in (C0.4Cu0.6)Sr2(Y0.86Sr0.14)Cu2O7

Abstract An ordered arrangement of carbon and copper atoms in the new compound (C 0.4 Cu 0.6 )Sr 2 (Y 0.86 Sr 0.14 )Cu 2 O 7 was investigated by means of electron diffraction and high-resolution electron microscopy. Electron diffraction patters show diffuse superlattice reflections corresponding to a compositional modulation with periods in the range from 2 a to 3 a along the a -axis and 2 c along the c -axis. From observed high-resolution images, it is concluded that the modulated arrangement of carbon and copper atoms is responsible for the diffuse superlattice reflections. It is proposed that this modulated structure consists of two kinds of superstructure units having dimensions of 2 a × b ×2 c and 3 a × b ×2 c . There are two different atomic arrangements in the 3 a × b ×2 c units.

Structures and magnetic susceptibility of Ni-ion-introduced zeolite A and X

Ni-ion-introduced zeolite A (Ni-A) and X (Ni-X) were synthesized by the ion-exchange method, and their magnetic properties and crystal structures were investigated. Temperature dependence of magnetic susceptibility for Ni-A and Ni-X showed the presence of magnetic interaction and spin-glass behavior at low temperatures. The results of Rietveld analysis using powder X-ray diffraction patterns show that Ni ions are located at Na ion positions, with slightly different coordinates.

AgI-intercalation into Bi2Sr2CaCu2Oz compound

Abstract Polycrystalline AgI-intercalated Bi 2 Sr 2 CaCu 2 O z is prepared and the structure and physical properties studied. The lattice parameters a and c are determined to be 5.40 and 22.8 A, respectively. The expansion of the lattice parameter c is 7.4 A, compared with that of a Bi 2 Sr 2 CaCu 2 O z (Bi2212) specimen ( c/2: 15.4 A ). This expansion is more than twice as large as that of iodine-intercalation (3.6 A). The EPMA measurement shows that the I/Ag ratio in the AgI-intercalated specimen is greater than 1.0. The T c is 69 K, which is lower than that of Bi2212 (75 K) and almost the same as that of IBi 2 Sr 2 CaCu 2 O z (IBi2212, 67 K). The effect of AgI-intercalation on the superconductivity is discussed.