R. Kanno

Perovskite-type oxides as oxygen electrodes for high temperature oxide fuel cells

Abstract Polarization and electrical conductivity measurements were made at 800°C in open air using the perovskite-type oxides La 1− x Sr x MO 3 (M  Cr, Mn, Fe, Co) sputtered on ytteia stabilized zirconia electrolyte. The lowest cathodic polarization overpotential and the highest conductivity were obtained for the LaCoO 3 electrode at 800°C. The overpotential varied depending on the pre-annealing temperature and period of the electrodes. At the annealing temperature of 800°C, the cathodic overpotentials for La 1− x Sr x CoO 3 did not vary significantly with the annealing period, and at 1000°C increased with it. This increase of the overpotentials was interpreted in terms of a reaction between the electrolyte and the La 1− x Sr x CoO 3 electrode. LaCoO 3 and La 0.7 Sr 0.3 CoO 3 reacted with the electrolyte to form La 2 Zr 2 O 7 and Sr 2 ZrO 4 , respectively, at 1000°C. With La 0.7 Sr 0.3 MO 3 (M  Cr, Mn, Fe), no reaction between the electrodes and the electrolyte was observed at 1000°C and Sr 2 ZrO 4 was observed at 1100°C.

Crystal chemistry and physical properties of La2−xSrxNiO4 (0 ≤ x ≤ 1.6)

Abstract Structural, transport, and magnetic data for the system La 2−x Sr x NiO 4 , 0 ≤ x ≤ 1.6, are reported. The oxygen content of the system was controlled by annealing under various oxygen partial pressures below 150 atm and was determined by iodometric titration. A Rietveld analysis of the room-temperature powder X-ray diffraction data showed that the tetragonal distortion of the NiO 6 octahedra decreases monotonically with increasing x for 0 ≤ x ≤ 1.4, but the La(Sr)O(2) bond length increases anomalously in the interval 0 ≤ x ≤ 0.6. A semiconductor-metal transition decreases monotonically with increasing x from about 675 K(x=0) to 20 K(x=1.2). Samples with x > 1.0 exhibited a weak ferromagnetic moment at 5 K and the onset of a positive component in the Hall effect. Comparison of the La 2−x Sr x CuO 4 and La 2−x Sr x NiO 4 systems shows that the superconductive copper oxides have the equilibrium Cu 3+ + O 2− = Cu 2+ + O − shifted to the right and, for x = 0, antiferromagnetic correlation in a half-filled σ x 2 − y 2 band whereas the weakly ferromagnetic nickel oxides have the equilibrium Ni 4+ + O 2− = Ni 3+ + O − shifted to the right, but ferromagnetic correlations in a quarter-filled σ∗ band.

Carbon as negative electrodes in lithium secondary cells

The charge and discharge behaviors of lithium cells with carbon electrodes have been examined in 1 M LiClO4 in PC/DME electrolyte. The thermal decomposition products of poly(2-chloro-1-phenylacetylene) and the carbon fiber M46 showed a high anode performance in lithium secondary cells. The lithium storage mechanism was examined by XPS and X-ray diffraction measurements. The intercalated lithium ions participate mainly in the highly reversible cell reaction.

Crystal chemistry and transport properties of Nd2-xAxNiO4 (A = Ca, Sr, or Ba, 0 ≤ x ≤ 1.4)

Structural and electrical properties of the system crystallizing in the K2NiF4 structure, Nd2−xAxNiO4 (A = Ca, Sr, or Ba, 0≤x≤1.4), were studied. The solid solution limits of alkaline earth were 0.6, 1.4, and 0.6 for Ca, Sr, and Ba, respectively. Oxygen content was controlled by annealing under various oxygen pressures below 150 atm. Powder X-ray diffraction data were analyzed by the Rietveld method to determine the bond lengths. In the case of the Sr-substituted system, tetragonality in the lattice parameters, c/a, shows a maximum at x = 0.6, while distortion of a NiO6 octahedron, Ni−O(2) (//c-axis)/Ni−O(1) (//a-axis), monotonically decreases from 1.13 (x=0) to 1.04 (x = 1.4). No Jahn-Teller distortion appears in a Ni3+ region. A metal-semiconductor transition is observed for O

Structure and properties of YBaSrCu3Oy (y=6.2−7.3)

Abstract Sintered YBaSrCu 3 O y was treated at 300–950°C under various oxygen pressures of P O 2 =0.2−5×10 4 atm. The structure as observed by powder X-ray diffraction (XRD) changed with increasing oxygen content from tetragonal ( y ⩽6.6) to orthorhombic ( y ⩽7.0) to tetragonal ( y ⩾7.0). The maximum orthorhombic distortion and the highest superconducting transition temperature where reached at y =6.90−6.95. The orthorhombic structure for y =6.95 refined by a Reitveld analysis of the XRD data was essentially the same as that of YBa 2 Cu 3 O 6.9 . On the other hand, transmission electron microscopic studies of the latter tetragonal structure strongly suggested ordering of Cu(1)-O chains in microdomains with sizes of 50×50 A 2 , the XRD “tetragonal” symmetry being only an averaged one. The transition temperature, T c , was 82 K at y =6.90, while 80 K at y =7.20. The concentration of carrier holes as estimated from the Hall effect was 4.9×10 21 cm -3 at y =6.90 and 3.9×10 21 cm -3 at y =7.20 at 100 K. Excess oxygen has been supposed to be concentrated in microdomain boundaries where Cu ions get octahedrally coordinated, leading to the reduction of the carrier concentration.

Ionic conductivity of solid lithium ion conductors with the spinel structure: Li2MCl4 (M = Mg, Mn, Fe, Cd)

Abstract The ionic conductivity of the polycrystalline samples of the lithium chloride spinel, Li 2 MCl 4 (M = Mg, Mn, Fe, Cd) is measured by the help of ac techniques in the temperature range of 25–500°C. The highest conductivity of 0.3 Scm −1 at 400°C is obtained in Li 2 CdCl 4 . In addition, the solid solution, Li 2−2 δ M 1+ δ Cl 4 , has been examined. It is found that Li 1.9 Cd 1.05 Cl 4 has higher conductivity than that of Li 2 CdCl 4 . The phase transitions of these compounds are also discussed.

Lithium organic electrolyte cells using the copper chevrel phase as cathode

Abstract The copper Chevrel phase, CuxMo6S8−z (x=0–4, z=0-0.2), was evaluated as the cathodes in lithium organic electrolyte cells. The cells Li Cu x Mo 6 S 8− z showed a good discharge performance for the charge transferred range of 0.5 to 3.5 electron(e) Cu x Mo 6 S 8− z under a high current density such as 3mA/cm2. The charge and discharge cycle tests of the Li Cu 2 Mo 6 S 7·8 cell indicated a good rechargeability for the range of 0.5 to 2.5 e Cu x Mo 6 S 8− z . The electrode reaction mechanism was discussed with the help of x-ray diffraction analysis of the cathode reaction products.

Annealing effects on the Pb-doped 2223 phase under various temperatures and oxygen pressures

Abstract Annealing effects on the Pb doped 2223 type superconductor Pb0.35Bi1.73Sr1.89Ca1.86Cu3.0Oy at various temperatures (200– 800°C) and oxygen pressures (PO2=0.2–500 atm and in vacuum) are reported. XRD, SEM and TEM examinations indicated that the annealing below 800°C under oxidizing atmosphere generally brought about a segregation of a Ca2PbO4-like phase and (Sr,Ca)2CuO3 on the surface of the original particles. The particles of the 2223 phase kept their shape and remained well-crystallized but changed to a lead-poor or lead-free composition as seen from a change in the structural modulation wave length from 47 A to 27 A. These results have strongly suggested that these two modulation modes correspond to different chemical compositions, one rich in Pb as Pb/Bi≅ 1 5 and the other Pb free, Pb/Bi≅0. Under PO2⪖100 atm at 300°C the oxygen content in the remaining 2223 phase seemed to have increased as suggested from a contraction of the c-axis. When the annealing temperature was raised to 600°C at PO2=100 atm, a complete decomposition to a perovskite phase, (Sr,Ca) (Pb,Bi)O3, CuO and Ca2PbO4 occurred surprisingly. Under reduced oxygen pressures, the precipitation did not occur.

Chromium oxides as cathodes for lithium cells

Abstract The performances of organic electrolyte lithium cells with the chromium oxides, Cr 2 O 3 , CrO 2 , Cr 5 O 12 , Cr 2 O 5 , Cr 6 O 15 , and Cr 3 O 8 , as cathodes, have been examined. The discharge behaviors of the couples Li/Cr 2 O 5 , Li/Cr 6 O 15 , and Li/Cr 3 O 8 , gave satisfactory results, especially in terms of energy density. The highest calculated energy density, based on the weights of the chromium oxides and to a 2.0 V cutoff at 0.5 mA/cm 2 , was 1210 W h/kg for the Li/Cr 3 O 8 couple. Further, the performance of a coin-type cell with a Cr 3 O 8 cathode was demonstrated, and it was found that the cell exhibited good rechargeability.

Thermal decomposition and electrical conductivity of M(OH)3 and MOOH (M=Y, lanthanide)

The thermal decomposition of M(OH)3 (M=Y, La, Nd, Sm, Gd) with the Y(OH)3 structure was examined by the TG and DTA methods. Y(OH)3, Nd(OH)3, and Sm(OH)3 decomposed to MOOH and then to M2O3. The decomposition of La(OH)3 and Gd(OH)3 occurred via the following schemes: La(OH)3→LaOOH→La2O3·1/2H2O→La2O3, and Gd(OH)3→Gd2O3·3/2H2O→GdOOH→Gd2O3. The highest conductivity of 5.9×1o−9Scm−1 at 250°C was found in Gd(OH)3 and that of 8.9×10−7 S cm−1 400°C in GdOOH. The continuous-wave 1H NMR absorption spectrum of LaOOH at room temperature exhibited no doublet line shape. This shows that protons are magnetically isolated from each other, and very little H2O and H3O+ can exist.