Tsuyoshi Kajitani

Low-Temperature Thermoelectric Properties of the Composite Crystal [Ca 2CoO 3.34] 0.614[CoO 2]

Electric resistivity, thermoelectric power and thermal conductivity of a polycrystalline sample of the composite crystal [Ca2CoO3.34]0.614[CoO2], also known as Ca3Co4O9, have been measured below 300 K. Metallic conductivity accompanied by large thermoelectric power has been observed down to 50 K. At 300 K, the sample exhibits a thermoelectric power of S = 133 µVK-1, resistivity of ρ= 15 mΩcm and thermal conductivity of κ= 9.8 mWK-1cm-1. The resulting dimensionless figure of merit becomes ZT300 = 3.5×10-2, which is comparable to the value reported for a polycrystalline sample of NaCo2O4, indicating that the title compound is a potential candidate for a thermoelectric material.

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 of Bi2Te3 films by electrodeposition

Bismuth telluride films have been electrochemically deposited from solutions of Bi 2 O 3 and TeO 2 in diluted HNO 3 (pH = 0.50) onto Ti sheet working electrodes at 293 K. A conventional three-electrode cell was used with a platinum wire counter electrode and Ag/AgCl (saturated KCl) reference electrode. Single-phase films of Bi 2+x Te 3-x solid solution have been prepared from E = -200 to + 80 mV (versus Ag/AgCl). The films prepared at +20≤E≤ + 60 mV exhibit strong {110} orientation, while those prepared at +60 < E ≤ + 80 mV show remarkable {1 0 5} orientation. Both the a-axis and c-axis lengths are almost independent of the cathodic potential for E < - 100 mV. Above -100 mV, the a-axis length gradually decreases and the c-axis length increases with cathodic potential, implying the Bi concentration in the Bi 2-x Te 3-x solid solution moves from the stoichiometric value. The films prepared at E< + 20 mV show p-type conduction, while those prepared at +20 ≤ E ≤ + 80 mV show n-type conduction. The largest Seebeck coefficient, S = -63 μVK -1 (300 K), has been observed for the film deposited at E = +20 mV.

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 ).

Crystal Structures of YBa2Cu3-δAδO9-γ (A=Ni, Zn and Co)

A structural study of orthorhombic YBa2Cu3O6.94, YBa2Cu2.8Ni0.2O6.85 and YBa2Cu2.7Zn0.3O6.75, and tetragonal YBa2Cu2CoO7.16 by means of X-ray and time-of-flight type (TOF) neutron diffractometers was carried out to determine the locations of the dopant atoms, Ni, Zn and Co, in the 1-2-3 (Y/Ba/Cu) oxide. The nickel atoms occupy only the Cu2 site 2q(00z) with z=0.36. The zinc atoms occupy the Cu1 site 1a(000) and the Cu2 site with occupancies of 0.20(5) and 0.05(2). In the tetragonal YBa2Cu2CoO7.16, cobalt atoms were found at both the Cu1 and Cu2 sites with occupancies of 0.83(2) and 0.08(1).

Structural, Magnetic and Thermoelectric Properties of Delafossite-type Oxide, CuCr1-xMgxO2 (0 ≤x ≤0.05)

We report structural, magnetic and high-temperature thermoelectric properties of Delafossite-type oxide, CuCr_1-xMg_xO ₂ (0⩽ x ⩽0.05). Lattice parameter, c, linearly decreases with increasing Mg concentration in the range, 0⩽ x ⩽ 0.03. This decrease is mainly caused by the shrinking of O-Cu-O dumbbells which connect the CdI₂-type (Cr/Mg)O₂ slabs. Magnetic susceptibility measurements indicate that Cr³⁺ is in the high spin state in the paramagnetic phase above 25 K. Electrical resistivity, ρ, of CuCr_1-xMg_xO₂ exhibits semiconducting behavior (dρ/dT < 0) in the range from 350 K to 1100 K and becomes lower through the partial substitution of Mg ²⁺ for Cr³⁺ in 0 ⩽ x ⩽ 0.03. Due to positive Seebeck coefficients, S, of these oxides, it is natural to assume that the dominant charge carriers of CuCr_1-xMg_xO₂ are positive holes. Experimental values of S at 1100 K have consistency with the theoretical values predicted from Koshibaes formula. From the linear S vs. lnσ plot, it is estimated that the observed power factor, S²σ, reaches the maximum value around x = 0.03 in this system. The thermal conductivity, κ, for CuCr_1-xMg_xO₂ ranges from 6 to 10 W·m^-1·^-1 at 300 K. The maximum dimensionless figure of merit, ZT = S²T/ρκ, of the sample with x = 0.03 is 0.04 at 950 K

Preparation and Chemical Composition of Superconducting Oxide Tl2Ba2Can-1CunO2n+4 with n=1, 2 and 3

Superconducting oxides of Tl2Ba2Can-1CunO2n+4 with n=1, 2 and 3 were synthesized, and their structure and chemical composition were examined by X-ray powder diffraction, EPMA, Rietveld analysis and electron microscopy. Partial substitution of Tl with Ca was confirmed, but the production of holes in Cu layers expected from this substitution was rather small for a 120 K superconductor. Charge transfer of Tl3-δ-Cu2+δ would provide both the hole in the Cu-O bond required for high Tc and s-like electron of Tl atoms for stabilization of layered structures.

Structural study on high-Tc superconductor Bi2−x(Ca, Sr)3Cu2+xO9−y

The crystal structure of the high-Tc Bi2-x(Ca, Sr)3Cu2+xO9-y with x=0.2 and y=0.78 was studied by means of neutron and X-ray powder diffraction. Since the unit cell parameters were relatively large for powder diffraction analysis, an averaged structure was refined, assuming an orthorhombic sub-cell (a=5.39 A, b=5.39 A and c=30.37 A) which corresponds to 1/5 of the unit cell: This is a derivative of Bi4Ti3O12. The double perovskite unit interleaved by the double bismuth layers is B-type, i.e. a CuO6 octahedron is surrounded by eight alkaline earth metal ions. The pyramidal CuO5 configuration is found in this oxide. The copper valency is estimated at about 2.3 on the basis of the determined chemical composition.

Crystal structure and superconductivity controlled by cation substitution and oxygen annealing in y1-xcaxba2cu3oyand yba2-xlaxcu3oy

The effects of Ca2+ substitution for Y3+ and La3+ substitution for Ba2+ in YBa2Cu3O7 on the structural and superconducting properties were studied to control the average copper charge. Single-phase tripled perovskites were obtained for 0x0.2 and 0x1.0 for Ca and La doped series, respectively. A slight decrease of Tc with increasing x was found for small x values for both kinds of substituted specimens prepared by furnace cooling in air. Oxygen annealing experiments were also carried out. These suggested that the superconduction in the Y-Ba-Cu-O system cannot be interpreted only by oxygen content or average copper charge.