Yusuke Ujihira

CO2 absorption properties and characterization of perovskite oxides, (Ba,Ca) (Co,Fe) O3−δ

Abstract Perovskite oxides, Ba 0.95 Ca 0.05 Co 1−x Fe x O 3−δ , were found to be useful as materials for CO 2 absorption at high temperatures between 900 to 1123 K, and CO 2 absorbed perovskite oxides were characterized by Mossbauer spectrometry. Before absorption of CO 2 , a magnetic sextet with sharp peaks and two paramagnetic doublets due to Fe 3+ and Fe 4+ were observed for the cubic oxides with x > 0.4. Perovskite oxides with lattice oxygen vacancies, which were produced at high temperature, easily absorbed CO 2 . After absorption of CO 2 , the paramagnetic peaks disappeared and magnetic fields were produced due to less interaction of lattice oxygens with iron atoms, where CO 2 reacted with lattice oxygen to form CO 3− ions. Finally only one magnetic sextet with sharp peaks remained. It was considered to be due to α-Fe 2 O 3 with a small magnetic field, dispersed in BaCO 3 matrix.

Diffusion coefficients of positronium in amorphous polymers

Diffusion coefficients of positronium (Ps) have been determined for polysulfone (PSF), polycarbonate (PC) and polystyrene (PS) by means of positron lifetime spectroscopy. 2,2′-Dinitrobiphenyl (DNB) was added to the polymers as a Ps quencher, and the diffusion coefficients were determined from measured Ps quenching rate constants, assuming that the reaction between Ps and DNB was diffusion controlled. It is shown that the diffusion coefficients of Ps at 25 °C are (2.6–3.2)× 10–6 cm2 s–1, two–three orders of magnitude larger than those of oxygen, nitrogen and argon. The effect of DNB on Ps formation is briefly discussed.

DOPING MECHANISMS OF SN IN IN2O3 POWDER STUDIED USING 119SN MOSSBAUER SPECTROSCOPY AND X-RAY DIFFRACTION

The doping mechanism of Sn in In2O3 (ITO) powder was investigated using 119Sn transmission Mossbauer spectroscopy (TMS) and X-ray diffraction (XRD) in view of the chemical state of Sn. Deconvolution analyses of TMS spectra revealed that there was substitutional Sn4+ coordinated not only by 6 oxygen atoms [SnIn] but also by 7 or 8 oxygen atoms, for the samples with doping concentrations higher than 5 at.%. The amount of such electrically deactivated Sn4+ (coordination number of 7 or 8) increased with increasing doping concentration, which was quantitatively consistent with the decrease in doping efficiency. Precise XRD analyses indicated a systematic increase in the lattice constant with increasing doping concentration from 0.5 to 7 at.%. The increase in lattice constant was explained in terms of a repulsive force among tetravalent [SnIn] (coordination number of 6) with higher effective charge than In3+, which was also consistent with the results on the coordination of Sn4+ obtained through TMS analyses.

Gas sensitivity of metal oxide mixed tin oxide films prepared by spray pyrolysis

Various kinds of SnO2 films, modified with the addition of iron, antimony, copper, titanium, manganese, nickel, cobalt or calcium oxides, were fabricated by using the spray pyrolysis technique and their gas-sensing characteristics were studied. From electrical measurements in air, the relative sensitivity towards inflammable gas of these SnO2-based film sensors was compared. It was observed that SnO2-based films of higher electrical resistance had a tendency to have higher sensitivity towards ethanol than the SnO2-based films of lower resistance. The addition of p-type metal oxides, such as NiO and MnO, to the SnO2 matrix was found to be effective in increasing the sensitivity towards inflammable gas.

Donor Compensation and Carrier-Transport Mechanisms in Tin-doped In2O3 Films Studied by Means of Conversion Electron 119Sn Mössbauer Spectroscopy and Hall Effect Measurements

Donor compensation and carrier-transport mechanisms in tin-doped indium oxide (ITO) thin films were investigated, from the viewpoint of chemical state of tin atoms, by conversion electron Mossbauer (CEM) spectroscopy and Hall effect measurement. Carrier density (ne) and Hall mobility (µH), changed with the post-deposition anneals. The carrier density decreased with air-anneal and increased with reducing atmosphere. Analyses of the CEM spectra indicated that the decrease in ne with air-anneal was attributed to the compensation of tin donors by excess interstitial oxygen (tin-oxygen complex). Also, we could explain the increase in ne with reducing atmosphere in terms of the dissociation of the tin-oxygen complex. From the analyses of µH, we arrived at the possibility that the tin-oxygen complex behaved as the screened dipole scattering center.

Chemical state analysis of corrosion products on a steel by exposing it in SO2 (0.16 vol%) environment by means of conversion electron mössbauer spectrometry (CEMS)

Abstract Chemical states of iron compounds produced on a steel surface in SO 2 (0.16 vol%) environment were investigated non-destructively and the formation of FeSO 4 · H 2 O as the initial, FeSO 4 ·4H 2 O as the intermediate and γ-FeOOH as the final corrosion product was confirmed by analysis of CEM spectra. For the purpose of showing the depth profile of iron compounds of the corrosion layer, depth selective CEM spectra were measured by selecting the energy of re-emitted electrons. It was found that the ferric compound located at the uppermost surface was substituted by the ferrous compound at greater depth. The utility of CEMS applied to the corrosion study of a steel was demonstrated.

Estimation of free volume in polystyrene-polyphenylene ether blend probed by the positron annihilation lifetime technique

Abstract Variations of size, content and size distribution of free volumes in linear polystyrenes (PS) synthesized by radical processes, with the addition of miscible polyphenylene ether (PPE) in PS, were observed by positron annihilation lifetime measurements. The average free volume radius of polystyrene was proved to increase from 0.30 nm (PPE: 0%) to 0.34 tun (PPE: 100%) and the average intensity, relevant to free volume content, decreased with the increase of PPE. The size distributions of free volume of various PS to PPE ratios also reveal that average free volume size increases and that smaller free volumes decrease by the increase of PPE ratio. The evidence that the size distribution curve of PS and PPE mixture (1:1) is more similar to that of PS suggests that free volumes produced in PS are stable with the addition of PPE and that more positroniums annihilate in smaller free volumes generated in PS than in bigger ones formed by PPE, since numbers of free volume overwhelm those of PPE.

Free volumes and their distribution in crosslinked polysiloxanes probed by positron annihilation lifetime technique

In order to correlate the size, numerical concentration, and size distribution of free volumes with the nanostructure of crosslinked polysiloxane (cured MQ resin), free volumes of polysiloxanes of different degree of crosslinkage polysiloxanes were observed by positron annihilation lifetime measurements in the temperature range from 30 K to room temperature. The free-volume diameters of the highly crosslinked polysiloxane were found to be larger in the temperature range studied and their distributions become broader above Tg (150 K) than those for the lowly crosslinked polysiloxane, whereas free volume contents (number density) were lower for the highly crosslinked polysiloxane. The results suggest the heterogeneous and distorted nanostructure of prepolymers in the highly crosslinked polysiloxane.

Conversion Electron Mössbauer Spectrometric Study of Corrosion Products of Iron Immersed in Sodium Chloride Solution

Abstract The corrosion products of iron formed in 3% sodium chloride solution under various conditions of temperature, pH values of the solution, concentrations of dissolved oxygen, and durations of immersion were analyzed by conversion electron Mossbauer spectrometry (CEMS) at room and dry ice temperatures (297 and 200 K), paying particular attention to β-FeOOH formation in aqueous media. Although -γ-FeOOH was a major product of iron corrosion in sodium chloride solution containing 5 to 6 ppm dissolved oxygen in the temperature range of 18 to 45 C, it was found that β-FeOOH could be formed on the iron surface under the special conditions of pH 6 to 8, 0.5 to 1 ppm concentration of dissolved oxygen and higher temperature. The mechanism of the β-FeOOH formation in sodium chloride solution is discussed.

Preparation of Na+-selective electrodes by ion-implantation of lithium and silicon into single-crystal alumina wafer and its application to the production of ISFET

ZusammenfassungNa+-selektive Elektroden wurden durch Einbau von Si+ und Li+ in Aluminiumoxidblättchen hergestellt und ihre Charakteristiken untersucht. Die Blättchen hatten eine Dicke von 100 μm und einen Durchmesser von 1,40 cm. Ebenso wurde die Membran für einen ISFET hergestellt. Die Gesamtmenge von Li+ und Si+ wurde auf 1013–1015 Ionen/cm2 eingestellt, wobei sich bei 1014 oder 4×1014 Ionen/cm2 die beste Charakteristik ergab.Die Responsekurven der mit 1014 Ionen/cm2 versehenen Aluminiumoxidplättchen hatten eine Neigung von 42 mV/pNa in einem Konzentrationsbereich von 1–10−4mol/l. Der nach 1 min erhaltene volle Response war reproduzierbar. Die vorgeschlagene Technik wurde zur Einstellung der Gate-Oberfläche des Feldeffekt-Transistors auf Natriumion benutzt. Der Na+-sensitive FET (Na+-ISFET), der durch Einbau von Li+ und Al+ mit 5×1014 Ionen/cm2 hergestellt wurde, zeigte eine Neigung der Signalkurve von 30 mV/pNa in einem Bereich von 1–10−4mol/l.SummarySodium ion-selective electrodes (Na+-ISE) were prepared by implanting Si+ and Li+ into alumina wafers and their characteristics were investigated. The alumina wafer had a thickness of 100 μm and a diameter of 1.40 cm. The ionselective membrane was produced by ion-implanting of Li+ and Si+ on both sides of a single-crystal alumina wafer. The total doses of Li+ and Si+ were controlled to be the same, viz. 1013–1015 ions/cm2. The ion-implanted alumina wafer with 1014 or 4×1014 ions/cm2 of Li+ and Si+ showed better characteristics than the others.The response curves of the 1014 ions/cm2 implanted alumina wafer had a slope of 42 mV/pNa in a concentration range from 1–10−4mol/l. The full response achieved after about 1 min was reproducible. The proposed idea of producing Na+-ISE by ion-implantation technique was applied to functuate the gate surface of the field effect transitor to sodium ion. The sodium ion-sensitive FET (Na+-ISFET) prepared by implanting Li+ and Al+ at a dose of 5×1014 ions/cm2 showed a slope of 30 mV/pNa in a concentration range from 1–10−4mol/l.