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Abstract: Ln2Zr2O7 (Ln=Yb, Y, Gd, Eu, Sm, Nd, La) system changed from fluorite (F)-type to pyrochlore (P)-type phases when the ionic radius ratios, r(Ln3+)/r(Zr4+), were larger than 1.26. The oxide-ion conductivity showed sharp maximum at the vicinity of the phase boundary between the F- and P-type phases. The frequency dependence of dielectric constant () and dielectric loss factor () were successfully explained by the superimposition of Debye-type polarization due to dopant-vacancy associate and electrode–electrolyte interfacial polarization by the numerical calculation. The peak of dielectric loss tangent (tan δ) was ascribed to the dopant-vacancy associate. The εr (0) and dielectric constant of the associate (εr 0) showed also the maximum values at the vicinity of the phase boundary between the F- and P-type phases. [Copyright &y& Elsevier]

Abstract: Dielectric relaxations were investigated for the solid solution system Ce1−x Nd x O2−δ (0.0≦ x ≦0.5) having a fluorite-type structure, which is a typical oxide-ion conductor. The dielectric constants showed anomalously large values at low frequencies and high temperatures. Numerical analysis of frequency dependence of dielectric constant (ε r′) clarified that the anomalously large ε r′ originated from the superimposition of both Debye-type polarization and interfacial polarization between electrolyte and electrode. Two kinds of Debye-type relaxations observed were ascribed to defect associates, (NdCe′− V O¨)· and (NdCe′− V O¨−NdCe′) x . The Debye-type polarizations were also confirmed by analyzing the dielectric loss factor (ε r″). When the oxide-ion conductivity decreased in the heavy Nd-doped samples, both the Debye-type and the interfacial polarizations also decreased, suggesting that ordering of oxygen vacancy suppressed the electric field response of Debye-type polarization, resulting in the decrease of oxide-ion conductivity. [Copyright &y& Elsevier]

Abstract: The relationship between oxide-ion conductivity and ordering of oxide ion in the (Y1−x La x )2(Ce1−x Zr x )2O7 system having a pyrochlore-type composition was investigated. The crystal phase of the system with a variable cation radius ratio, but with a constant lattice parameter, changed from a rare-earth-C (C)-type phase to a pyrochlore (P)-type phase through a fluorite (F)-type phase with increase in the composition (x), depending on the cation radius ratio r(A3+)/r(B4+), which is a measure of ordering degree of oxygen vacancies. The oxide-ion conductivity increased once up to x =0.15, and then decreased with increasing x. This change of the electrical conductivity was understood on the basis of the ordering degree of oxide ion. The Rietveld analyses of X-ray and neutron diffraction patterns, and Raman spectroscopy supported the ordering effect of oxide ion on the conductivity. [Copyright &y& Elsevier]

The electrical conductivity of the LaY1−xInxO3 (x=0.0–0.7) system has been studied from the viewpoint of crystal chemistry. The high temperature form of LaYO3 (x=0.0) was ascertained to be the Sm2O3-type (B-type rare earth) structure, not perovskite-type one. The X-ray diffraction (XRD) experiments revealed that the samples with x=0.05 and 0.10 were the mixed phase of Sm2O3-type and perovskite-type structure, and changed to perovskite phase in the range of x≧0.20. From oxygen partial pressure dependence of the electrical conductivity, it was found that both the Sm2O3-type and the perovskite-type single phases showed hole conduction, but the mixed phase did oxide-ion one. The electrical conductivity of the LaY1−xInxO3 (x=0.0–0.7) system increased with increasing x, and showed the maximum value in the range of x=0.05–0.10, and then decreased with increasing x. The occurrence of oxide-ion conduction was discussed from the viewpoint of lattice distortion in the mixed phase. [Copyright &y& Elsevier]

Semiconducting oxide nanoparticles are strongly influenced by surface-adsorbed molecules and tend to generate an insulating depletion layer. The interface between a noble metal and a semiconducting oxide constructs a Schottky barrier, interrupting the electron transport. In the case of a Pt catalyst supported on the semiconducting oxide Nb-doped SnO 2 with a fused-aggregate network structure (Pt/Nb-SnO 2 ) for polymer electrolyte fuel cells, the electronic conductivity increased abruptly with increasing Pt loading, going from 10 -4 to 10 -2 S cm -1 . The Pt X-ray photoemission spectroscopy (XPS) spectra at low Pt loading amount exhibited higher binding energy than that of pristine Pt metal. The peak shift for the Pt XPS spectra was larger than that of the Pt hard X-ray photoemission spectroscopy (HAXPES) spectra. For all of the spectra, the peaks approached the binding energy of pristine Pt metal with increasing Pt loading. The Sn XPS spectral peak proved the existence of Sn metal with increasing Pt loading, and the peak intensity was larger than that for HAXPES. These spectroscopic results, together with the scanning transmission electron microscopy with energy dispersive X-ray spectroscopy (STEM-EDX) spectra, proved that a PtSn alloy was deposited at the interface between Pt and Nb-SnO 2 as a result of the sintering procedure under dilute hydrogen atmosphere. Both Nb spectra indicated that the oxidation state of Nb was +5 and thus that the Nb cation acts as an n-type dopant of SnO 2 . We conclude that the PtSn alloy at the interface between Pt and Nb-SnO 2 relieved the effect of the Schottky barrier, enhanced the carrier donation from Pt to Nb-SnO 2 , and improved the electronic transport phenomena of Pt/Nb-SnO 2 .

We synthesized Pt and PtRu catalysts supported on Nb-doped SnO(2-δ) (Pt/Sn0.99Nb0.01O(2-δ), PtRu/Sn0.99Nb0.01O(2-δ)) for direct oxidation fuel cells (DOFCs) using poly oxymethylene-dimethyl ether (POMMn, n = 2, 3) as a fuel. The onset potential for the oxidation of simulated fuels of POMMn (methanol-formaldehyde mixtures; n = 2, 3) for Pt/Sn0.99Nb0.01O(2-δ) and PtRu/Sn0.99Nb0.01O(2-δ) was less than 0.3 V vs RHE, which was much lower than those of two commercial catalysts (PtRu black and Pt2Ru3/carbon black). In particular, the onset potential of the oxidation reaction of simulated fuels of POMMn (n = 2, 3) for PtRu/Sn0.99Nb0.01O(2-δ) sintered at 800 °C in nitrogen atmosphere was less than 0.1 V vs RHE and is thus considered to be a promising anode catalyst for DOFCs. The mass activity (MA) of PtRu/Sn0.99Nb0.01O(2-δ) sintered at 800 °C was more than five times larger than those of the commercial catalysts in the measurement temperature range from 25 to 80 °C. Even though the MA for the methanol oxidation reaction was of the same order as those of the commercial catalysts, the MA for the formaldehyde oxidation reaction was more than five times larger than those of the commercial catalysts. Sn from the Sn0.99Nb0.01O(2-δ) support was found to have diffused into the Pt catalyst during the sintering process. The Sn on the top surface of the Pt catalyst accelerated the oxidation of carbon monoxide by a bifunctional mechanism, similar to that for Pt-Ru catalysts.