Shigeomi Takai

Diffusion coefficient measurement of lithium ion in sintered Li1.33Ti1.67O4 by means of neutron radiography

Neutron radiography (NR) using cold neutron beam was applied to the tracer diffusion coefficient measurement of lithium ion in Li1.33Ti1.67O4. The diffusion couples with different lithium isotope concentrations were annealed at 860 to 900°C and the isotope profiles of lithium ion in the sample were measured by NR. The diffusion profiles obtained for the samples annealed at higher temperatures show good agreement with Fick’s law, whereas the diffusion was not carried out well at the interface for the lower-temperature-annealed samples. The values of diffusion coefficients obtained from the profile fitting were a little smaller than those expected from the electric conductivity. The NR method was found to be the most useful method to measure the tracer diffusion coefficient of lithium ion in solids.

Powder neutron diffraction study of Ln-substituted PbWO4 oxide ion conductors

Abstract Structure refinements have been carried out on pure and lanthanide-substituted PbWO4 using powder neutron diffraction, and the defect structures of La- and Pr-substituted PbWO4 are discussed. The Rietveld refinement structure of pure PbWO4 agreed well with previous results. In the Pb1−xLaxWO4+x/2 system, the oxide ion interstitials seemed to be rather localized around z=0.3 of the 8e position (0 0 z) or the adjacent general position of the scheelite structure-type with I41/a symmetry. The deduced interstitial position is considered in terms of the oxide ion conduction path. A similar defect structure has been determined for the praseodymium-substituted compound, Pb1−xPrxWO4+x/2. In contrast, Pb1−xLa2x/3WO4-type substitution resulted in the formation of a cation-deficient structure.

Ionic conduction properties of Pb1−xMxWO4+δ (M = Pr, Tb)

Pb{sub 1{minus}x}M{sub x}WO{sub 4+{delta}} (M = Pr, Tb) compounds with scheelite-type structure were synthesized and their conduction properties at higher temperatures were investigated. With the substitution of praseodymium or terbium ions, a large enhancement in conductivity of pure PbWO{sub 4} was observed and the transport number of oxide ions was found to be almost unity. Irrespective of the changeable valence of lanthanide ions substituted, conduction properties and defect structures of these systems were found to be similar to those of the other lanthanide (La or Sm)-substituted PbWO{sub 4}.

Lithium ion conduction in scheelite-type oxides and analysis of lithium ion motion by neutron radiography

Abstract New solid solutions of A 1− x Li 2 x BO 4 (A=Ca, Sr or Ba, B=W or Mo) with a scheelite-type structure were synthesized and the lithium ionic conduction were confirmed by electrochemical measurements and neutron radiography (NR). Irrespective of A-site cations, the conductivities for molybdates were higher than tungstates. The highest conductivity was observed at the composition of x =0.05 in each system. NR analysis showed that, the lithium ion conduction would be ascribed to interstitial lithium ions in Ca 0.95 Li 0.1 MoO 4 , although the fairly big lithium ion diffusion due to thermal effect was observed.

Studies on the lithium ion conduction in Ca0.95Li0.10WO4 using cold neutron radiography

Abstract Cold neutron radiography (CNR) was applied to study the lithium ion conduction in the substituted scheelite-type oxide of Ca 0.95 Li 0.10 WO 4 . The lithium ion distribution profiles were obtained from a set of neutron radiography (NR) images of the electrolyzed oxides having different 6 Li/ 7 ratios. They showed that the lithium ion transport number of the oxide is 0.99, which coincided with the value derived from the EMF measurement of an oxygen gas concentration cell. Furthermore, they denoted that the lithium ion conduction was preferably ascribed to lithium ions in the interstitial sites.

Properties of the perovskite-type oxide ceramic Ca1 − xLa2x3MnO3 − δ as the cathode active materials in alkaline batteries

The substituted complex oxides shown by Ca1 − xLa2x3MnO3 − δ, where the average valence of Ca-site is designed to always be double, have the perovskite-type structure in the range of x ≤ 0.90. These sintered oxides show high electronic conductivity of more than 101 S cm−1 at room temperature even in the porous state (porosity 50 to 60%). The sintered porous ceramics work as cathode active materials without any conductive additives in alkaline solutions. The discharge performance changes depending on the x value in Ca1 − xLa2x3MnO3 − δ and the kind of alkaline solution. The discharge capacity is 225 mAh g−1 (810 C g−1) for the x = 0.1 sample in 5% LiOH solution. This is comparable to that of the real cathode mixture composed of MnO2 and graphite in alkaline manganese batteries.

Tracer diffusion experiments on LISICON and its solid solutions by means of neutron radiography

Abstract Lithium ion diffusion coefficient measurements were carried out on LISICON (Li 3.5 Zn 0.25 GeO 4 ) and on a zinc-rich analogue (ZRA; Li 3 Zn 0.5 GeO 4 ) using neutron radiography (NR). Smearing 6 LiNO 3 -saturated solution on a surface of a rectangle-shaped sample consisting of 7 Li and subsequent annealing enabled the relatively low temperature diffusion experiment down to 300 °C. The measured isotope concentration profiles agreed well with the diffusion model from the surface into the semi-infinite media, and the diffusion coefficients can be obtained for both LISICON and ZRA in the temperature range between 300 and 500 °C. The diffusion coefficient of LISICON is essentially larger than that of ZRA, while similar a Haven ratio was found. This indicated that the larger conductivity in LISICON was mainly caused by the higher lithium ion mobility and not by the difference of diffusion path.

Defect properties of mechanically alloyed La-substituted PbWO4

Abstract Mechanical alloying (MA) technique has been applied to prepare the PbWO 4 -based scheelite-type solid solutions at room temperature. In the case of La-substitution, the scheelite-type single phase can be obtained by 12 h milling. The solubility range of lanthanum ions was 0≤ x ≤0.4 in the form Pb 1− x La x WO 4+ x /2 and 0≤ x ≤1.0 in the composition of Pb 1− x La 2 x /3 WO 4 . The latter case includes La 2/3 WO 4 , which cannot be obtained by the conventional sintering method. From the powder density measurements, the mechanically alloyed samples were supposed to prefer the charge compensation by forming cation vacancy rather than by forming oxide ion interstitials, in these lanthanum-substituted PbWO 4 s.

Conductivity relaxation phenomena of the oxide ion conductor Zn2-2xTi1+xO4

Abstract Impedance measurements were carried out on the oxide ion conductor Zn 2−2 x Ti 1+ x O 4 in the frequency range between 20 Hz and 10 6 Hz below 600°C. The frequency dependence of the electric modulus M ″ shows the double peak shape in the cubic structure. These results are different from the previously studied Zn 2− x /2 Ti 1− x Ta x O 4 system where the single and double peaks have been observed for cubic and tetragonal phases, respectively. The M ″ profile of the present system was not significantly varied with the composition and activation energies could be obtained from both lower- and higher-frequency peaks. The lower-frequency relaxation was supposed to be related to the long-range ion hopping, since the activation energy obtained from the lower frequency peak is close to that from the conductivity

Conductivity Relaxation Study on (Bi2O3)1−x(Y2O3)x and (Bi2O3)1−x(Gd2O3)x with the Defect Fluorite Structure

Abstract In order to investigate the conductivity phenomena below 400°C in high-temperature-type oxide ion conductors of (Bi2O3)1−x(Y2O3)x and (Bi2O3)1−x(Gd2O3)x, impedance spectra were measured in the frequency range between 20 Hz and 1 MHz. The conductivity relaxation phenomena observed were studied in terms of the electric modulus formula. The relaxation frequencies were found to show Arrhenius-type behavior and the activation energies were in good agreement with those obtained by high temperature electric conductivity.