Seiichi Suda

Preparation of Li4Ti5O12 and LiCoO2 thin film electrodes from precursors obtained by sol–gel method

Thin films of Li4Ti5O12 and LiCoO2 were prepared from precursors obtained by a sol–gel process using poly(vinylpyrrolidone) (PVP) followed by a heat treatment at 600–800 °C. Both thin films were characterized with X-ray diffraction method and cyclic voltammetry (CV). The Li4Ti5O12 and LiCoO2 thin films have spinel structure and layered rock salt structure, respectively. Their crystallinity was comparable with those for highly crystallized samples. The thickness of both films was about 1 μm after three times of the sol–gel process followed by the heat treatment. An orientation of the thin films was observed. The electrochemical characteristics for both films were comparable with those for standard powder samples.

Synthesis of MgO–SiO2 and CaO–SiO2 amorphous powder by sol–gel process and ion exchange

Abstract The processing of binary or ternary metal–oxide spherical powders often provides ideal starting materials for the preparation of ceramics or glasses, and the use of these powders can lead to excellent properties. Amorphous spherical powders composed of SiO2 and MgO or CaO were synthesized by using Na2O–SiO2 spherical powder as a starting material and then conducting ion-exchange between the magnesium or calcium ions and the sodium ions in the Na2O–SiO2 powder. The maximum amount of magnesium or calcium in the powder was Mg/Si=0.5 or Ca/Si=0.8. The ratios of Mg/Si and Ca/Si were then determined by controlling the alkaline-earth concentration of the suspension used for the ion exchange. The ratio of Mg2+ or Ca2+ to consumed Na+ as a result of the ion exchange was estimated to be 1.0, and it was found that OH− around Si–ONa also participates in the ion exchange. The ratio of water to ethanol in the reaction mixture also influenced the ion exchange.

29Si NMR of ethoxytrimethylsilane hydrolysis and sodium ion exchange

Abstract Hydrolysis and condensation of ethoxytrimethylsilane (ETMS) and sodium alkoxide (NaOR (R  CH3, C2H5 and C4H9)) were investigated by 29Si NMR spectroscopy. The question of Na bonding to Si across oxygen in a dried gel and the resulting NaOSi bond is discussed. A shift in the NMR signal with time was observed in the ETMSNaORD2O system, but not in the solution without NaOR. The shifting velocity was dependent on the NaOR R group and the magnetic field to which the signal shifted decreased with H+ concentration. This signal shift can be attributed to the change of environment surrounding SiO− and this is suggested as the process of the SiONa linkage formation.

Effects of Lanthanum on the Electrical Conductivity of CuO Ceramics.

Lanthanum was dissolved in CuO and the effects of La on the electrical conductivity of CuO were investigated in order to control the hole concentration and clarify the conduction mechanism of CuO that exhibits a p-type semiconductivity. The maximum amount of La dissolved in CuO was evaluated to be 0.5 mol% by powder X-ray diffraction. The conductivities for La-doped CuO were investigated by 4-probe and 3-probe methods. The temperature dependence of conductivity showed that CuO has two conduction mechanisms in the temperature range of 50°C to 900°C; conductivity at more than 600°C was independent of atmosphere and the amount of La, whereas conductivity below 500°C increased with an increase in partial oxygen pressure (PO2 ) and amount of La. Surface conductivity at 200°C was especially influenced by PO2 , and the sensitivity of surface conductivity to PO2 increased with doping of La into CuO. The doping of La led to a change of chemisorbed oxygen species from O2- to O2- and resulted in an increase in sensitivity to PO2 .

The effects of sodium ion on hydrolysis and condensation of diethoxydimethylsilane

Abstract The effect of sodium ion on hydrolysis and condensation of diethoxydimethylsilane (DEDMS) was investigated by 29Si NMR spectroscopy. Discussed were the possibility of SiONa linkage through sol-gel processes and the difference of structure for the solutions between with and without sodium ions. 29Si NMR signals shifted with time for the solution containing NaOH. The shift depended on both OH− and Na+ ion concentration of the solution and would be attributed to the exchange reaction between sodium ion and proton of SiOH. The exchange was observed for the solution with more than pH = 13.0. When sodium ion was added into the solution mixed with DEDMS and H2O, the proportion of cyclic trimer and tetramer decreased and the molecular weight of condensed species are also reduced, because the sodium ion played the role of a terminator.

Morphology of calcium carbonate coating on amorphous silicate powder

The amorphous silicate powders containing sodium, calcium,barium and magnesium were prepared by sol-gel and ion-exchangemethod, and calcium carbonate was coated on the powders for thepurpose of industrial re-circulation of calcium carbonate. Thecalcium carbonate powder with micro pores was obtained bycoating on amorphous CaO-SiO2 powder, and the pore sizedistribution would be influenced by calcium on the surface ofthe powder. The coating on amorphous MgO-SiO2 powderresulted in a hedgehog-like powder, which allowed needle-likecrystal extended radially, and the coated powder was the mixedphase of aragonite and calcite. The use of amorphousBaO-SiO2 and Na2O-SiO2 powders also led to the coatingpowder with the single phase of calcite. The morphology ofcalcium carbonate coating would be ascribed to cations on thesurface of the amorphous silicate powders, because the amount ofcations that would be dissolved in soaking solution was smalland insufficient to affect the morphology.

Synthesis of Na+ superionic conductor in the Na2O-Y2O3-P2O5-SiO2 system by the gelation induced by moist air or N2

Abstract Sodium superionic conductors in the system Na 2 O-Y 2 O 3 -P 2 O 5 -SiO 2 were prepared by sol-gel method: humidity-controlled air or N 2 was passed into the reaction mixture to avoid precipitates such as nitrate and carbonate. Highly homogeneous xerogel was obtained by supplying water at a rate of about 1.8 × 10 −4 mol min −1 . The sintered samples of the xerogels with the composition between x = 5.33 and 5.60 in Na x Y 0.8 P 0.4 Si 3.6 O 12.0 showed a single crystal phase with the superionic conduction. The sample with the composition of x = 5.33 showed highly ionic conductivity of ϱ 300 = 13.9 Ω cm at 300 °C.

Synthesis of Na+ superionic conductors of sodium yttrium silicophosphates by a sol-gel method

Abstract Sodium superionic conductors with the composition of Na 5.20 Y 0.80 P 0.40 Si 3.60 O 12.0 were prepared using highly homogeneous powders synthesized by reactions of alkoxides. The single phase specimen with highly ionic conductivity o ϱ 300 =9.47 Ω cm at 300°C was obtained by sintering in N 2 . The grain sizes of samples obtained by using metal alkoxides were 2–3 microm and the grain growth was promoted. The addition of calcia improved sinterability.

Formation mechanism of amorphous Na2O–SiO2 spheres prepared by sol–gel and ion-exchange method

Abstract Mono-disperse Na2O–SiO2 (NS) amorphous spheres were synthesized by sol–gel and ion-exchange method, the latter involving ion exchange between alkali ion and proton of OH group that is formed by hydrolysis of metal alkoxide. The compositions, particle sizes and particle dispersion of NS spheres were investigated to clarify their formation mechanism. NS spheres containing sodium at the Na/Si ratio less that 0.9 were obtained without aggregation. The Na/Si ratios of NS spheres were controlled relatively easily employing various batch compositions, and the variation of Na/Si ratios of NS spheres with the batch compositions was almost independent of hydroxypropyl cellulose (HPC) species. The particle size of NS spheres was increased with an increase in amount of sodium included in NS spheres, and the rate of particle growth was increased with a decrease in molecular weight of HPC. HPC contributed not directly to the formation of NS spheres but to the dispersion of initial NS particles, and large HPC molecule inhibited the growth of NS spheres because of steric hindrance of HPC. Sodium played a role as a catalyst of condensation, which promotes the formation of Si–O–Si bonding.

Preparation of (La, Li)TiO 3 Dense Ceramics using Sol-Gel and Ion-Exchange Process

Lithium ionic conductor, (La, Li)TiO 3 , has synthesized with La/Li-TiO 2 amorphous spheres that were obtained by sol-gel and ion-exchange method, and succeeding La 3+ /Li + partial ion exchange. In this work, La /Li ion exchange conditions were mainly investigated in order to obtain dense (La, Li)TiO 3 ceramics that have highly ionic conductivities. La + /Li + ion exchange behavior was changed with ion-exchange solutions, and the Li/Ti ratio was increased with an increase in ethanol/water ratio in the solvent used for La 3+ /Li + partial ion exchange. The use of an adequate ethanol/water ratio resulted in La/Li-TiO 2 amorphous spheres with the composition of La/Li/Ti=0.54/0.34/1.00, and sintering of the spheres at 1200°C for 5 h in air led to dense (La, Li)TiO 3 ceramics which exhibit the conductivity of 4.0 × 10 -3 S cm -1 at 25°C.