Jukichi Hombo

Electrical conductivities of SrFeO3−δ and BaFeO3−δ perovskites

Abstract The conductivities and the Seebeck coefficients of the SrFeO3−δ and the BaFeO3−δ perovskites were measured in air, O2, and N2 in the temperature range from 650°C to room temperature. The carrier densities and the mobilities were calculated by using a small polaron hopping model. All the samples of the BaFeO3−δ show the hopping conduction, while the conductions of the SrFeO3−δ in air and O2 will be near metallic because the carrier densities and the mobilities are very large. The mobilities rather than the carrier densities decreased with the increase of the amounts of the oxygen vacancy, δ, in the range of 0

Origin of the silver doping effects on superconducting oxide ceramics

The origin of silver doping effects on Y‐Ba‐Cu‐O superconducting ceramics, such as a high‐temperature shift of the point at zero resistivity in resistivity measurements and an increase in critical current density, was sought by transmission electron microscopy observations. Sintering was strongly promoted together with suppression of the formation of the liquid phase in the grain boundaries by silver. Consequently, the liquid phase, which is not a superconductor, was not present in almost all the grain boundaries of the silver‐doped ceramics, while this phase was present in almost all the grain boundaries in pure ceramics.

A new preparation method of barium titanate perovskite film using electrochemical reduction

Abstract BaTiO 3 perovskite film was prepared by electrochemical reduction in the solution containing both Ba 2+ and Ti 4+ ions. Heat-treatment at temperatures higher than about 700°C was necessary for crystallization, because the as-deposited oxide films were amorphous. The deposition occurred on stainless steel, Fe, Ni and Ti electrodes, but not on Pt and Al electrodes during the electrolysis. The composition of the deposited oxide film was strongly dependent on the applied potential and current density during the electrolysis. It was judged from the measured voltammogram that the incorporation of Ba 2+ ion into the deposited oxide during the electrolysis depends on electrochemical reduction in which H 2 O is consumed to produce OH − ion. Consequently, Ba 2+ ion existed as a nitrate and a hydroxide or an oxide in the hydrated TiO 2 owing to this electrochemical reduction. The mechanisms of the deposition of the BaTiO 3 precursor and the crystallization of perovskite by heat-treatment are discussed.

Ag doping effects on the superconduction of Bi(Pb)SrCaCuO ceramics

Abstract We have studied the silver doping effects on the superconducting and the morphological properties of the Bi(Pb)SrCaCuO ceramics. Silver promotes the c-axis orientation and the crystallization of the 80 K phase, produces the decrease in the resistivity at room temperature and the high-temperature shift of the Tc for the BiSrCaCuO system. Silver will catalyze the intergranular coupling of the 80 K phase grains in these ceramics. Zero resistivity was attained at 104 K by Ag doping in the Pb substituted system which did not consist of the 110 K single phase. This result also suggests that Ag catalyze the intergranular coupling of the 110 K phase grains in the ceramics. When Ag was partially substituted for Ca, the single phase of the 110 K phase was obtained in the Pb containing ceramics sintered in air for 140 hours.

A New Preparation Method of LaMnO3 Perovskite Film on SrTiO3 Electrode

Photoelectrochemical deposition of the LaMnO 3 precursor was investigated on SrTiO 3 and TiO 2 single-crystal semiconductor electrodes [(100) plane] in solutions containing Mn 2+ and La 3+ ions. Deposition of the LaMnO 3 precursor was always observed on the SrTiO 3 electrode, but not on the TiO 2 electrode. Pre-electrolysis of the TiO 2 electrode in solutions containing La 3+ ion was necessary for the LaMnO 3 precursor deposition. Thus, the LaMnO 3 precursor deposition needs perovskite or perovskite-like conditions at the electrode surface

Ag doping effects on the superconduction of YBa2Cu3Oy ceramics

We have studied the Ag doping effects on the superconduction of YBa2Cu3Oy ceramics. Three type systems of the nominal composition, i.e., YBa2−xAgxCu3Oy, YBa2Cu3−xAgxOy, and YBa2Cu3Oy·Agx (x=0.1, 0.3, 0.7), were used as the Ag substituted and doped samples, and were compared each other in the structural, morphological, and superconducting properties. Ag is substituted for Cu in preference to Ba, although Ag is not completely substituted for these cations in the range of x>0.1. Ag promotes the crystallization and c-axis orientation in Y-Ba-Cu systems, especially in the case of the presence of Ba vacancy. Ag will catalyze the intergranular coupling of the superconductor grains in the ceramics, even if relatively large amount of the impurity phases are present. The Tc slightly shifts to higher temperature and the Jc increases by the nominal Ag substitution for Cu. This result suggests that the Ag substituted superconductor phase for Cu has the higher Tc and larger Jc than those of the non-doped phase.

A new electrochemical synthesis of iron spinel oxide in LiOH

In this paper, a new method of the electrochemical synthesis of iron spinel oxide in pure LiOH solution is reported

Effect of La3+ ion on the electrodeposition of manganese and cobalt oxides

Abstract Electrochemical preparations of oxide films of the perovskite (ABO 3 where A = La, B = Mn, Co) type are based on the electrodeposition of B oxides from solutions containing cations of both A and B. The effect of La 3+ ions on the electrodeposition of manganese and cobalt oxides and the chemical state of these ions in the oxides were investigated. Amorphous hydrous MnO 2 and Co 2 O 3 were deposited with an incorporation of La 3+ ions in the mixed solutions Mn(NO 3 ) 3 + La(NO 3 ) 3 and Co(CH 3 COO) 2 + La(NO 3 ) 3 respectively. The La/Mn and La/Co atomic ratios in the deposits were strongly dependent on the La(NO 3 ) 3 concentration in the solutions. The presence of La 3+ ions increased the overpotential of the electrochemical oxidation of Mn 2+ and Co 2+ ions in the solutions, resulting in suppression of the electrodeposition of the oxides. It was presumed from inductively coupled plasma atomic emission spectroscopy, Fourier transform IR spectroscopy and X-ray photoelectron spectroscopy measurements that La 3+ ions in the Mn and Co oxides deposited from the solutions containing La(NO 3 ) 3 combined strongly with O 2− ions as in La 2 O 3 .

Analysis of hydration number in cobalt oxyhydroxide films using the quartz crystal microbalance

The hydration numbers n of the deposited cobalt oxyhydroxide (CoOOH · nH2O) films were measured using an in-situ quartz crystal microbalance, and the effect of the La3+ ion on the hydration was studied. The hydration number of the deposited film was very high during the initial stage of the electrolysis (n > 10), but decreased to a constant value. The constant values of the hydration number were about 3 and 1 for CoOOH · nH2O films deposited in Co(CH3COO)2 and in other solutions (Co(NO3)2, CoCl2, CoSO4) respectively. The anion effect of CH3COO− on hydration was discussed. The incorporation of an La3− ion increased the hydration number by about 5. Consequently, CoOOH · nH2O · La3+ · 5H2O was proposed for the composition of the deposited cobalt oxyhydroxide film containing La3+ (atomic ratio LaCo = 1). The combination state of La3+ in this composition was also discussed.

Effect of La3+ ions on the deposition of nickel oxide

Abstract The effect of La3+ ions on the deposition of nickel oxide (NiOOH) in solutions containing both La3+ and Ni2+ ions was studied. La3+ ions suppressed a growth of NiOOH by their inocorporation into the deposit in the deposition process. The rate of La3+ incorporation is low compared with that of the NiOOH deposition. The limiting value in the atomic tatio of La/Ni in the deposit was about 1–2 when NiOOH was deposited under a low deposition rate.