Yukio Morii

Modulated Structure of the Thermoelectric Compound [Ca2CoO3]0.62CoO2

We have determined the crystal structure of the composite crystal [Ca 2 CoO 3 ] 0.62 CoO 2 , known as Ca 3 Co 4 O 9 , by a superspace group approach. Structural parameters were refined with a super...

Preparation and crystal structure of Sr2CuO2(CO3)

Abstract Sr 2 CuO 2 (CO 3 ) was prepared at 1273 K and 0.01 MPa CO 2 partial pressure in a flowing gas of O 2 CO 2 using a mixture of SrCO 3 and CuO powders as a starting material. The compound has a tetragonal structure with lattice constants a = 7.8045(1), and c = 14.993(1) A , and its space group is 14. The formula per unit cell is 8 Sr 2 CuO 2 (CO 3 ), and measured and calculated densities are D m = 4.71 g/cm 3 , and D x = 4.81 g/cm 3 , respectively. The crystal structure was refined by Rietveld analysis on X-ray powder diffraction and neutron powder diffraction data. The final residuals ( R F ) were 4.31 and 4.27% for the X-ray and neutron data, respectively. The structure consists of deformed [CuO 6 ] octahedrons and layers of ordered triangular CO 3 groups. Sr atoms having eight near oxygen neighbors are between the [CuO 6 ] octahedrons and the CO 3 layers.

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 ).

Magnetic properties of the antiferromagnetic double perovskite Ba2PrRuO6

The ordered perovskite compound Ba2PrRuO6 is prepared and its magnetic properties are investigated. The Rietveld analysis of the neutron diffraction profiles measured at 150 K shows that the Pr3+ and Ru5+ ions are arranged with regularity over the six-coordinate B sites of the perovskite ABO3 and that Ba2PrRuO6 belongs to space group P21/n, with a = 6.0063(5), b = 5.9863(4), c = 8.4677(7) A and 90.04(2)°. The magnetic susceptibility and the heat capacity measurements show that this compound transforms to an antiferromagnetic state below 117 K. From the neutron diffraction patterns measured at 7 K, the magnetic structure is determined to be of Type I and the magnetic moments of Pr3+ and Ru5+ are estimated to be 2.2(1) and 2.0(2) µB, respectively. Their values are discussed on the basis of theoretical calculations for the crystal field splitting.

Lattice Instability in Cubic Cu69.2Al25.4Ni5.4 Related to Martensitic Phase Transition

The dispersion relation of [110] TA 1 phonon ( e //[1\bar10]) of β 1 -phase Cu 69.2 Al 25.4 Ni 5.4 was measured extensively at 261, 295 and 372 K by neutron scattering technique. It was found that the dispersion surface of the transverse acoustic mode has a pronounced valley along the [110] axis. The temperature dependence of the phonon energy shows a partial softening of the phonon mode. An anomalous dip of the dispersion curve was observed around q =(2/3) q max on the [110] axis. Interplaner force-constant analysis revealed that the lattice dynamics of the crystal indicates dual instabilities both to the 2H and 18R type martensites. Quasielastic scattering was investigated on and in the vicinity of the [110] axis. Peaks attributable to the 2H and 18R martensites were observed as functions of temperature, which also indicates that 2H and 18R are competing.

High‐resolution neutron powder diffraction study on nitrogenated Nd2Fe17

High‐resolution neutron powder diffraction measurements with λ=1.8232 A and collimation of 6’‐20’‐6’ on Nd2Fe17Nx with x=0, 2.85, and 2.91 were carried out at room temperature. Structural parameters and magnetic moments were determined by the Rietveld profile‐fitting calculation. The magnetic moments of iron atoms increased with increasing nitrogen concentration; e.g., the magnetic moments of iron located at 6c, 9d, 18f, and 18h sites increase from less than 0.7μB in the x=0 sample to about 2.1μB in the x=2.91 sample. It is noticed that a local atomic group composed of two Fe(1) atoms at the 6c site plus six Fe(3) atoms at the 18f site keeps its shape against the nitrogen uptake.

Design of Engineering Diffractometer at J-PARC

An engineering diffractometer designed to solve many problems in materials science and engineering including investigations of stresses and crystallographic structures within engineering components is now being developed at J-PARC project. This instrument views a decoupled-poisoned liquid H2 moderator providing neutrons with good symmetrical diffraction profiles in the acceptable wavelength range. The primary flight path and the secondary flight path are 40 m and 2.0 m, respectively, for 90 degree scattering detector banks. A curved supermirror neutron guide will be installed to avoid intensity loss due to the long flight path and to reduce backgrounds from fast neutrons and gamma rays. Therefore, stress measurements with sufficient accuracies in many engineering studies are quite promising. The optimization of this instrument has been performed with a Monte Carlo simulation, and an appropriate resolution of less than 0.2 % in d/d has been confirmed. A prototyped radial collimator to define a gauge width of 1 mm has been designed and manufactured. From performance tests conducted at the neutron diffractometer for residual stress analysis RESA in JRR-3 of Japan Atomic Energy Agency, the normal distribution with a full width at half maximum of 1 mm was obtained in a good agreement with the simulation.

Magnetic and neutron diffraction studies on double perovskites A2LnRuO6(A = Sr, Ba; Ln = Tm, Yb)

Magnetic properties of double perovskites A2LnRuO6 (A = Sr, Ba; Ln = Tm, Yb) have been reported. Powder neutron diffraction measurements have been performed at 10 K and higher temperatures (≥100 K) to determine their crystal and magnetic structures. As a result of the Rietveld analysis of the diffraction profiles, it is found that they are monoclinic with space group P21/n (A = Sr) or cubic with space group Fmm (A = Ba). From the magnetic susceptibility and specific heat measurements, a magnetic transition at 36–48 K is observed in each compound. The neutron diffraction data collected at 10 K show that this magnetic transition is due to a long range antiferromagnetic ordering involving both Ru5+ and Ln3+ ions. Each of the magnetic moments of Ru5+ and Ln3+ orders in a type I arrangement.

Modulated Structure of Misfit Layered Cobalt Oxide [(Ca0.90Bi0.10)2(Co0.95Bi0.05)O3]pCoO2

We have determined the crystal structure of Bi-substituted and Bi-free misfit layered cobalt oxides [Ca2CoO3]0.62CoO2, by a (3+1)-dimensional superspace group approach. Structural parameters have been refined with a superspace group of C2/m(1p0)s0 using powder neutron diffraction data. Bismuth atoms are found to substitute for both Ca and Co atoms in the rock salt-type [Ca2CoO3] subsystem. The resulting structural formula is expressed as [(Ca0.90Bi0.10)2(Co0.95Bi0.05)O3]pCoO2 with a refined b-axis ratio of p=0.6183. By Bi substitution, the modulation of the Co–O distances in the [Ca2CoO3] subsystem is markedly decreased relative to the Bi-free counterpart, whereas such a modulation in the [CoO2] subsystem is slightly increased. The observed increase in the Seebeck coefficient and electrical resistivity of the Bi-substituted phase can be explained in terms of the decrease in hole concentration in the CoO2 sheets.

Study on the crystal and magnetic structures of and by powder neutron diffraction

We prepared oxygen stoichiometric and in which tetravalent terbium ions are stabilized at the B sites of the perovskite . Their crystal structures at room temperature and at 10 K were determined from both x-ray and neutron diffraction measurements. Both and have an orthorhombic perovskite-type structure with space group Pnma (No 62). Magnetic susceptibility measurements have been performed for both the compounds in the temperature range between 4.5 K and room temperature. Both the compounds show the antiferromagnetic transition at . The temperature-dependent magnetic susceptibilities were measured with zero-field-cooled (ZFC) and field-cooled (FC) conditions at an applied field of 1000 G. A dramatic difference between ZFC and FC was observed below the Neel temperatures for both the compounds, which shows the onset of a ferromagnetic moment below those temperatures. To determine the magnetic structures at the antiferromagnetic state, powder neutron diffraction measurements have been performed at 10 K and room temperature. Both the compounds have the G-type magnetic structure in which terbium atoms are antiferromagnetically coupled with the six neighbouring terbium atoms.