The role of microstructure and processing on the proton conducting properties of gadolinium-doped barium cerate

Haile, Sossina M.; West, David L.; Campbell, J. A.

doi:10.1557/jmr.1998.0219

Cited by 238 publications

(166 citation statements)

References 26 publications

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“…If one assumes that the true dielectric constant of the grain boundaries and the bulk are comparable, then the ratio of the apparent capacitances, C gb /C bulk , is simply equal to the ratio of the grain diameter, D, to the grain-boundary thickness, ␦. 27 The temperature-averaged value of this ratio was found to be ∼140, and if one takes the grain-boundary thickness to be of the order of 2.5 nm (as has been observed in Gd-doped barium cerate 27 ), the implied grain size is of the order of 0.35 m. This value agrees well with the observed 0.46 m average grain size in the scanning electron microscopy (SEM) image and confirms the assignment of the midfrequency arc in the impedance spectra to grain-boundary processes.…”

Section: B Conductivity Of Byz By Impedance Spectroscopymentioning

confidence: 99%

“…The grain-boundary conductivity obtained from this simple calculation is a measure of both the grain-boundary geometry (i.e., sample microstructure) and the inherent properties of the grain boundaries. The specific grain-boundary conductivity (independent of microstructure), sp.gb , was determined, again, under the assumption that the true dielectric constants of the bulk and grain-boundary regions are equal, using the approximation 27 :…”

Section: B Conductivity Of Byz By Impedance Spectroscopymentioning

confidence: 99%

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Processing of yttrium-doped barium zirconate for high proton conductivity

2007

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The factors governing the transport properties of yttrium-doped barium zirconate (BYZ) have been explored, with the aim of attaining reproducible proton conductivity in well-densified samples. It was found that a small initial particle size (50-100 nm) and high-temperature sintering (1600°C) in the presence of excess barium were essential. By this procedure, BaZr 0.8 Y 0.2 O 3−␦ with 93% to 99% theoretical density and total (bulk plus grain boundary) conductivity of 7.9 × 10 −3 S/cm at 600°C [as measured by alternating current (ac) impedance spectroscopy under humidified nitrogen] could be reliably prepared. Samples sintered in the absence of excess barium displayed yttria-like precipitates and a bulk conductivity that was reduced by more than 2 orders of magnitude.

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Section: B Conductivity Of Byz By Impedance Spectroscopymentioning

confidence: 99%

Section: B Conductivity Of Byz By Impedance Spectroscopymentioning

confidence: 99%

Processing of yttrium-doped barium zirconate for high proton conductivity

2007

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“…Furthermore, recent work comparing polycrystalline conductors to single crystal conductors has demonstrated that the grain boundary interface plays a significant role in controlling the total conductivity [73]. Attaining a high level of understanding of grain-boundary microstructure as a function of composition and sintering conditions is critical to the design of new materials, whereby, the grain boundaries may be manipulated to optimize conductivity [74,75].…”

Section: Perovskitesmentioning

confidence: 99%

Review of proton conductors for hydrogen separation

Phair

Badwal

2006

Ionics

214

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There is a global push to develop a range of hydrogen technologies for timely adoption of the hydrogen economy. This is critical in view of the depleting oil reserves and looming transport fuel shortage, global warming, and increasing pollution. Molecular hydrogen (H 2 ) can be generated by a number of renewable and fossil-fuel-based resources. However, given the high cost of H 2 generation by renewable energy at this stage, fossil or carbon fuels are likely to meet the short-to medium-term demand for hydrogen. In view of this, effective technologies are required for the separation of H 2 from a gas feed (by-products of coal or bio-mass gasification plants, or gases from fossil fuel partial oxidation or reforming) consisting mainly of H 2 and CO 2 with small quantities of other gases such as CH 4 , CO, H 2 O, and traces of sulphur compounds. Several technologies are under development for hydrogen separation. One such technology is based on ion transport membranes, which conduct protons or both protons and electrons. Although these materials have been considered for other applications, such as gas sensors, fuel cells and water electrolysis, the interest in their use as gas separation membranes has developed only recently. In this paper, various classes of proton-conducting materials have been reviewed with specific emphasis on their potential use as H 2 separation membranes in the industrial processes of coal gasification, natural gas reforming, methanol reforming and the watergas shift (WGS) reaction. Key material requirements for their use in these applications have been discussed.

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“…The impedance spectra of all samples exhibited wellresolved arcs in the Nyquist representation that could be attributed to bulk (high frequency) and grain-boundary (lower frequencies) response, as well as a quasi-linear portion at the lowest frequencies, corresponding to the electrode response. 23 The bulk conductivity was obtained in the usual manner by correcting for the overall sample geometric factor, A/L, where A is the sample surface area and L the thickness. The temperature dependence of the bulk conductivity of BaCe 0.85 M 0.15 O 3-␦ (M ‫ס‬ Nd, Gd, Yb) in flowing water-saturated Ar is shown in Fig.…”

Section: A Structural Characteristics [Bamentioning

confidence: 99%

Defect chemistry and transport properties of Ba_xCe_0.85M_0.15O_3-δ

Espinosa

et al. 2004

J. Mater. Res.

102

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The site-incorporation mechanism of M 3+ dopants into A 2+ B 4+ O 3 perovskites controls the overall defect chemistry and thus their transport properties. For charge-balance reasons, incorporation onto the A 2+ -site would require the creation of negatively charged point defects (such as cation vacancies), whereas incorporation onto the B 4+ -site is accompanied by the generation of positively charged defects, typically oxygen vacancies. Oxygen-vacancy content, in turn, is relevant to proton-conducting oxides in which protons are introduced via the dissolution of hydroxyl ions at vacant oxygen sites. We propose here, on the basis of x-ray powder diffraction studies, electron microscopy, chemical analysis, thermal gravimetric analysis, and alternating current impedance spectroscopy, that nominally B-site doped barium cerate can exhibit dopant partitioning as a consequence of barium evaporation at elevated temperatures.

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The role of microstructure and processing on the proton conducting properties of gadolinium-doped barium cerate

Cited by 238 publications

References 26 publications

Processing of yttrium-doped barium zirconate for high proton conductivity

Processing of yttrium-doped barium zirconate for high proton conductivity

Review of proton conductors for hydrogen separation

Defect chemistry and transport properties of Ba_xCe_0.85M_0.15O_3-δ

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The role of microstructure and processing on the proton conducting properties of gadolinium-doped barium cerate

Cited by 238 publications

References 26 publications

Processing of yttrium-doped barium zirconate for high proton conductivity

Processing of yttrium-doped barium zirconate for high proton conductivity

Review of proton conductors for hydrogen separation

Defect chemistry and transport properties of BaxCe0.85M0.15O3-δ

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Product

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Defect chemistry and transport properties of Ba_xCe_0.85M_0.15O_3-δ