Noriko Sata

Proton transport properties at the grain boundary of barium zirconate based proton conductors for intermediate temperature operating SOFC

Proton transport properties across the grain boundary of barium zirconate based proton conductors were studied in accordance with the space charge concept. The analysis is performed at temperatures lower than 200 °C using a Mott-Schottky model. The barrier height of Y- and Gd-doped barium zirconate is in the range of 0.29 to 0.57 V, which higher than that of oxygen ionic conductors. The barrier height of the space charge layer shows a dependence on the dopant type and concentration. The dependence correlates with the enrichment of the dopant at the grain boundary. The results suggest that the enrichment of the dopant decreases the barrier height and is effective to improve proton transport properties across the grain boundary.

Protonic Conduction in the Single Crystals of SrZr0.95M0.05O3 (M=Y,Sc,Yb,Er).

The protonic conductivities of SrZr0.95M0.05O3 doped with four acceptor ions (M3+=Y3+, Sc3+, Yb3+, Er3+) have been studied in the single crystal form. The protonic conductivity is found in four acceptor ions, indicating that protons migrate by hopping from site to site. The Yb-doped crystal has the lowest activation energy and the highest conductivity amongst the four acceptor ions. This is considered to be due to the difference in strength of the O–H bond with different acceptor doping.

Optical absorption spectra of acceptor-doped SrZrO3 and SrTiO3 perovskite-type proton conductors

Abstract The optical absorption spectra were investigated to study the electronic structures of perovskite-type proton conductors. The fundamental absorption edge shifts to higher energy side when an acceptor ion was doped to the perovskite-type oxides. In SrZrO 3 , an absorption band was observed in the lower energy side of the fundamental absorption edge when an acceptor was doped. It is suggested that this band corresponds to the acceptor level of the proton conductors. The absorption of this band was enhanced when the proton was removed from the crystal. This suggests that the number of electrons in the acceptor level decreases when a proton is introduced to the crystal.

Fabrication of proton conducting thin films of SrZrO3 and SrCeO3 and their fundamental characterization

Abstract Proton conducting thin films of SrZrO 3 and SrCeO 3 were fabricated by the pulsed laser ablation method using ArF excimer laser. The thin films of SrCeO 3 and SrZrO 3 were grown in the [100] direction on the SrTiO 3 (100) substrate and in the [211] direction on the MgO(100) substrate and on the Al 2 O 3 substrate. The Raman scattering spectra show that the thin films grown in the low P O 2 contain lots of oxygen ion vacancies compared to bulk crystals.

Proton Transport and Microstructure Properties in Superlattice Thin Films Fabricated by Pulsed Laser Deposition

Superlattice thin films of the perovskite-type oxide proton conductor SrZr0.95Y0.05O3/SrTiO3 was fabricated by pulsed laser deposition. Their structural and proton transport properties were reported. X-ray diffraction analysis and selected area electron diffraction revealed that the thin films were epitaxially grown on MgO(001) substrate. High-density edge dislocations and a columnar structure were observed in the films by high-resolution electron microscopy. The in-plane electrical conductivity of the thin films was determined by impedance spectroscopy. The contribution of proton transport to the total conductivity of the films was confirmed by H2O/D2O exchange measurement. The conductivity of superlattice films was increased by introducing heterointerfaces. The high activation energy (Ea=1.0 eV) was explained by the grain-boundary effect of the columnar structure in the films.

Proton conduction in mixed perovskite-type oxides

Abstract Transparent solid solution crystals of Sr[CeZr] 0.95 Yb 0.05 O 3 were grown by the FZ-method using a Xe-arc imaging furnace to investigate proton conductivity in mixed perovskite-type oxides. It is observed that there are at least five different O–H stretching vibrational modes in these solid solutions and their intensities and peak wave numbers depend on the composition of Ce and Zr. The results of electrical conductivity showed that these materials are proton conductors as well as SrCe 0.95 Yb 0.05 O 3 and SrZr 0.95 Yb 0.05 O 3 . The IR-absorption intensity and the electrical conductivity have their maxima at x =0.8 in Sr[Ce x Zr 1− x ] 0.95 Yb 0.05 O 3 . The Raman spectra of solid solutions suggest that the lattice distortion was changed by addition of SrZr 0.95 Yb 0.05 O 3 to SrCe 0.95 Yb 0.05 O 3 .

Enhancement of Proton Transport in an Oriented Polypeptide Thin Film

Proton transport properties of a partially protonated poly(aspartic acid)/sodium polyaspartate (P-Asp) were investigated. A remarkable enhancement of proton conductivity has been achieved in the thin film. Proton conductivity of 60-nm-thick thin film prepared on MgO(100) substrate was 3.4 × 10(-3) S cm(-1) at 298 K. The electrical conductivity of the oriented thin film was 1 order of magnitude higher than the bulk specimen, and the activation energies for the proton conductivity were 0.34 eV for the oriented thin film and 0.65 eV for the pelletized sample, respectively. This enhancement of the proton transport is attributable to the highly oriented structure on MgO(100) substrate. This result proposes great potential for a new strategy to produce a highly proton-conductive material using the concept of an oriented thin film structure without strong acid groups.

Proton diffusion in SrZr0.95Y0.05O3 observed by quasielastic neutron scattering

Proton diffusion was observed in Y-doped SrZrO 3 ceramics above 500°C by quasielastic neutron scattering. The line width of the quasielastic component varies with energy transfer Q and temperature. The temperature dependence is well elucidated by the thermal activation-type proton migration with activation energy of 0.2 eV. The observed hopping distance was 1.7 A, which is comparable to one of the distances between two proton sites.

Electronic structures of protonic conductors SrTiO3 and SrCeO3 by O 1s X-ray absorption spectroscopy

The electronic structures of protonic conductors SrTi 1-x Sc x O 3 and SrCe 1-x Yb x O 3 have been studied by O 1s X-ray absorption spectroscopy (XAS). In SrTi 1-x Sc x O 3 , hole state and acceptor-induced level are observed in the band gap energy region. Such a structure is also observed in the O 1s XAS spectra of SrCe 1-x Yb x O 3 . The XAS structures and their temperature dependence reflect the activation energy estimated from electrical conductivity. These facts indicate that the conductivity is achieved by deep acceptor-induced level lying in the middle of the band gap.

Studies on the superlattice of perovskite-type proton conductors synthesized by pulsed laser ablation

Superlattices of perovskite-type proton conductors, SrCeO 3 , SrZrO 3 and SrTiO 3 were synthesized by pulsed laser ablation method to study the effect of lattice distortion on proton dynamics. The SrCeO 3 , SrZrO 3 thin films and their superlattices are grown in the [100] azimuth when they are fabricated on MgO(100) substrate and in the [211] azimuth when they are fabricated on SrTiO 3 (100) substrate or MgO(100) substrate with buffer layer of SrTiO 3 , XRD and Raman results suggest that the lattice distortion depends on the thickness ratio of the superlattice.