Katsuhiro Imai

Single Crystal X-Ray Structure Analysis of Bi2(Sr, Ca)2CuOx and Bi2(Sr, Ca)3Cu2Ox Superconductors

Average crystal structures of Bi2(Sr, Ca)2CuOx and Bi2(Sr, Ca)3Cu2Ox were analyzed using single crystal X-ray intensity data applying anisotropic temperature factors. Crystal data: Bi2Sr1.60Ca0.40CuO6, Bbmb, a=5.3826(8) A, b=5.3761(11), c=24.384(7), Rw=0.108 for 282 reflections; Bi2.06Sr1.70Ca1.24Cu2O8, Bbmb, a=5.3946(8), b=5.3895(13), c=30.649(12), Rw=0.064 for 354 reflections. Precession photographs show that Bi2Sr1.60Ca0.40CuO6 has a monoclinic modulated structure and Bi2.06Sr1.70Ca1.24Cu2O8 has an orthorombic one. The incommensurate modulated structures were qualitatively illustrated by using a modulation wave model.

Superconductivity and Crystal Structure of LaBa2Cu3-xOy Compounds

An extensive study of magnetic, electrical transport, and structural properties of the normal and superconducting states of LaBaCuO2BO3 are presented. A ceramic compound of LaBaCuO2BO3 has been synthesized by the solid-state reaction technique under ambient pressure by reacting BaCO3, La2O3, CuO and B2O3. LaBaCuO2BO3 compound was characterized by x-ray diffraction and scanning electron microscope-x-ray energy dispersion spectrum analyses. Rietveld refinement of powder x-ray diffraction data indicated that the compound is P4bm space group symmetry and a=5.57475(8), c=7.5056(l)A. Measured magnetic susceptibilities of powder specimens of LaBaCuO2BO3 compound indicate a transition to a diamagnetic state at 32 K.

Structure of the High Tc Superconductor, Ba2LaCu3-xO7-y –Studies on La-Ba Ordering and Oxygen Defects

Crystal structures of semiconductor Ba2LaCu3-xO7-y sample and 56.5 K superconductor sample, which was obtained by annealing the former in O2, were determined by X-ray Rietveld analysis. The ordering of Ba and La has been clarified by the use of the anomalous dispersion effects. An increase in the site occupancy factor of square planer oxygen (O(2):at z=0) around Cu(1) and shortening of Ba-O(2) distance were observed in the high Tc sample compared with the semiconductor. This oxygen behavior, i.e. formation of fully occupied square planer oxygen group (O(1)×2+O(2)×2) around Cu(1), determines the appearance of the superconductivity.

Single-Crystal X-Ray Structure Analysis of New Oxide-Superconductor Bi2(Sr1-xLnx)2(Gd1-yCey)2Cu2O10+z

The crystal structure of Bi2(Sr1-xLnx)2(Gd1-yCey)2Cu2O10+z (Ln=Gd with x=0.1, y=0.23 and z=0.16 or Ln=Ce with x=0.1, y=0.13 and z=0.16) was determined using the X-ray intensity data of a single crystal. The chemical composition was determined by electron microprobe analysis. The crystal data are as follows: orthorhombic, space group Cmmb, a=5.435(2), b=5.446(1), c=17.826(5) A, final R factor Rw=0.053 for 640 independent observed reflections. The structure is composed of stacking of the Bi-O double layer, a Cu-O sheet of CuO5 pyramids, and the fluorite-like Ln2O2 layer. Sr is located between the Cu-O sheet and the Bi-O double layer. The crystal has a commensurate type superstructure with unit cell dimensions b×9 and c×2 of the subcell: a=5.426(7), b=49.06(2), c=35.66(2) A. Precession photographs showed orthorhombic symmetry and systematic absences suggested condensed symbols C*c* for the space group of the superlattice. The modulation of the structure was well reflected on the anisotropic motions of the thermal ellipsoids of the component atoms in the average structure.

Second-Harmonic Generation of Blue Light in Epitaxial K3Li2-xNb5+xO15+2x Waveguides on K3Li2-x(Nb0.98Ta0.02)5+xO15+2x Substrates by Metalorganic Chemical Vapor Deposition

We report a new second-harmonic generation blue laser using a K3Li2-xNb5+xO15+2x single crystal film waveguide on a K3Li2-x(Nb0.98Ta0.02)5+xO15+2x crystal substrate by the metalorganic chemical vapor deposition method. Second-harmonic blue light with output power of 2 mW at 487 nm was successfully generated. The phase-matched wavelength bandwidth of the device was 1.3 nm, and the temperature coefficient of the phase-matched wavelength was 0.36 nm/°C. Crystallographic evaluation was also performed for the KLN thin film crystal. The (001) plane of KLN crystal film was well orientated to the (001) plane of the KLNT substrate, and the surface morphology of the film was very smooth. Moreover, it was revealed that an as-deposited KLN film crystal has a single domain structure.

K3Li2Nb5O15 Fiber and Plate Crystals

The growth and homogeneity of second harmonic generation (SHG) in K3Li2Nb5O15 (KLN)-type fiber and plate single crystals grown by the micropulling-down method are reviewed. The uniformities of fiber crystals up to 300mm long and plates up to 1 × 15 × 100mm in size were examined via lattice constant and SHG wavelength measurements. Fluctuations in composition along the growth axis were negligible. However, variations in the phase-matching wavelength along the radial direction were easily detected. The phase-matching wavelength decreases when the lithium content in the starting melt and the pulling-down rate are increased. Results from X-ray rocking-curve analysis of these crystals are reviewed, as are some optical measurements, such as those of the acceptance temperature and wavelength and the wavelength conversion ratio.

Structural Characterization of K3Li2Nb5O15 Single Crystals by Combining High-Resolution X-Ray Diffractometry and Topography

High-resolution multiple-crystal multiple-reflection X-ray diffractometry is used for the structural characterization of nonlinear optical single crystals of K3Li2Nb5O15 (KLN) grown by the micro-pulling-down (µ-PD) method. The combination of high-resolution X-ray diffractometry and topography shows that the lattice parameters along the c-axis (c-parameters) decrease towards the seed crystals, because of the decrease in the K content and increase in the Nb content. However, the KLN single crystals exhibit multi domain structures in which discontinuous changes in the c-parameters are periodically observed along the growth direction, despite the compositional change being continuous. Large mosaic structures due to discontinuous tilt in the lattice planes are also observed at the boundaries between the domains.