Yoshiki Takagi

Structural analysis of 2PbO·SiO2 glass

Abstract The short-range structure of 2PbO·SiO2 glass was investigated by X-ray diffraction analysis. Most of the Pb atoms form covalent PbO4 pyramids and dimeric or trimeric PbO4 pyramids form zigzag chains acting as glass formers. It is possible from a geometric point of view that Si2O76− dimer, Si3O108− trimer, Si4O128− tetrameric ring, SiO32− chain and ionic PbO6 octahedron bridge zigzag PbO4 chains. The present structural model for 2PbO·SiO2 glass gives a good agreement between the observed and calculated S versus Si(S) curves and is consistent with the results of Raman spectroscopy and direct chemical analysis for silicate groups as well as those of NMR for 207Pb.

The Effect of Substitution of La for Ba and Ce for Y on the Tc of Superconducting Ba2YCu3O7

It was found that La3+ enters the Ba-site of the high Tc superconductor Ba2YCu3O7-δ but Ce4+ does not enter the Y-site. Replacement of a small amount of Ba by La raises the transition temperature, Tc, but further increase of the La content results in a significant drop of the transition temperature. These results are interpreted in relation to the distribution of oxygen vacancy.

Superconductivity and magnetism in Co substituted YBCO compounds

Abstract Superconducting transition temperature Tc and magnetic susceptibility χ were measured on Co substituted YBCO system, YBa2[Cu1−xCox]3Oy. The observed characteristic dependence of Tc on the substitution concentration x w investigated taking the magnetic data into consideration. The operating mechanism of the Co ion at the Cu(I) site on the superconducting state in the [Cu(II)O] net-planes are inquired from the two viewpoints: (1) changes in electronic state and (2) magnetic moment induction at the Cu(II) site. The possibility of both being induced by displacement of the oxygen atom O(1) between Cu(I) and Cu(II) is considered.

Influence of Annealing Condition on the Superconducting Behavior of High-Tc Oxide (Ba2Y)Cu3O7-x

The influence of annealing condition is presented for high Tc superconducting oxide (Ba2Y)Cu3O7-x via investigation of the structure and electrical resistivity. It is found that Tc depends strongly on the annealing temperature and annealing time. Tc is higher for the sample with the greater orthorhombic distortion, that is, the greater difference between the lattice constant a and b.

Structural analysis of molten B2O3

The structure of molten B2O3 at ca. 650 °C has been investigated by the X-ray radial distribution method. The most likely two-dimensional quasi-crystalline model for the short-range arrangement is a mixed structure of boroxol rings and independent BO3 triangles. The estimated density for this model with an average inter-layer distance of 4.34 A is in good agreement with the observed density.

Structural analysis of some molten materials by X-ray diffraction. Part 5.—LiCl, PbCl2 and their mixtures

The molten structure of PbCl2, LiCl and their mixtures were examined by X-ray diffraction analysis. In molten Pbcl2, each Pb atom is surrounded by about eight Cl atoms at a distance of 2.92 A, which is near to the sum of the ionic radii of Pb2+ and Cl–. It is expected that only very few rigid complex anions will be present in molten PbCl2. The results of X-ray diffraction analysis in molten PbCl2 are consistent with those of Raman spectroscopy. The average Pb–Pb interaction in the molten state should be intermediate between a b.c.c. and an s.c. arrangement and the s.c. arrangement takes precedence with increasing LiCl concentration.

X-ray-diffraction analysis of the molten ZnCl2–KCl system

The structure of molten ZnCl2, 2ZnCl2·KCl, ZnCl2·KCl, and ZnCl2·2KCl have been examined by X-ray-diffraction analysis. The existence of a tetrahedral [ZnCl4] unit in these systems was confirmed from the first peak of the radial distribution function of each composition.

X-ray diffraction analysis of molten CdC12-type layer structures. I. CoCl2

Abstract The structure of molten CoCl2 has been examined by X-ray diffraction analysis. The nearest Co-Cl distance found was 2·39 A and the coordination number of cobalt was calculated to be 3·9. The existence of a tetrahedral CoCl4 unit has been confirmed from the first and second peak of the radial distribution function.

Structural analysis of molten PbCl2

The structure of molten PbCl2 has been re-examined by X-ray diffraction analysis. In molten PbCl2, each Pb atom is surrounded by three Cl atoms at an average distance of 2.63 A as well as four Cl atoms of 3.14 A. The average Pb—Pb interaction within 10 A is similar to a distorted f.c.c. arrangement.

Density and Refractive Index of the Molten MnCl2-KCl System

The densities and refractive indices of the molten MnCl2-KCl system were measured from melting temperature up to 1000°C. Both quantities decreased linearly with increasing temperature. The composition dependence of the refractive index showed an anomalous depression and was well correlated with that of the density. The molar refractivity of this system was almost a linear function of the composition in contrast to the density and refractive index. The similarity between the density and refractive index, and the volume expansion caused by complex formation are discussed.