Stability and Electric Conductivity of Barium Cerate Perovskites Co- Doped with Praseodymium (original) (raw)
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Journal of The Electrochemical Society, 2010
The chemical stability and electrical properties of three promising perovskite-related structures BaCe 0.8 Gd 0.15 Pr 0.05 O 3−␦ , BaCe 0.85 Sm 0.15 O 3−␦ , and BaCe 0.85 Eu 0.15 O 3−␦ were tested in air, humidified N 2 and H 2 , as well as in D 2 O + N 2. Powder X-ray diffraction studies confirmed the formation of a cubic perovskite-like structure. The change in the lattice constant was consistent with B-site substitution in BaCeO 3. All the investigated compounds formed barium carbonate in CO 2 at elevated temperatures and were found to be chemically unstable in boiling H 2 O. The data showed that these three compounds are chemically stable in humidified CH 4 at 800°C; however, at 600°C, the formation of barium carbonate was observed. The electrical conductivity in wet N 2 and/or H 2 was found to be higher than that in the D 2 O-containing atmosphere, confirming proton conduction in the doped BaCeO 3. The Gd + Pr co-doped BaCeO 3 showed the highest total conductivity of 2.58 ϫ 10 −2 S cm −1 in H 2 + 3% H 2 O at 700°C with an activation energy of 0.36 eV in the temperature range of 450-700°C.
Proton Conductivity Measurements in Yttrium Barium Cerate by Impedance Spectroscopy
Journal of the American Ceramic Society, 2004
Proton-conducting solid-electrolyte perovskite ceramics based on acceptor-doped barium and strontium cerates have become the focus of extensive investigations as candidate materials for fuel cells that operate at moderate temperatures. To assess the suitability of a material for this application, it is necessary that bulk electrolyte conductivity be measured at the operating temperature. However, very little reliable published conductivity data exist above 600°C. Protonic conductivity in yttriumdoped barium cerate has been observed to be less at high temperatures than would be expected, based on the activation energy and preexponential for hydrogen transport at temperatures <300°C. Conductivity data obtained from impedance spectroscopy on BaCe 0.9 Y 0.1 O 3-␣ over the extended temperature range of 100°-900°C are presented. An Arrhenius plot of the data shows two distinct linear regions, suggesting that two different rate-limiting processes occur in series with a breakover transition at ϳ250°C. The decrease in conductivity is apparently not due to dehydration. An activation energy for protonic transport of 0.26 eV, about one-half of the lowtemperature value, is proposed, based on curve fitting of the high-temperature data. . Comparison of BCY10 conductivity from this paper and calculated conductivity after Kreuer 7 at steam partial pressure of 0.023 MPa.
Properties of Perovskite-Type Proton Conductors
2013
Investigations of perovskite-type BaCeO3 and SrCeO2 with various dopants (Y, Gd, Nd, and Ni) indicate that their microstructures and electrical properties are strongly influenced by the type and amount of dopants. Grain growth and densification of sintered samples are influenced by dopant level and A:B site nonstoichiometry. The conductivity of BaCe1_Y039 increases with the yttrium content in hydrogen and wet Ar; and exhibits a maximum in oxygen at an yttrium content of 10 to 20%. BaCe08Y0203_1 has the highest conductivity in a hydrogen atmosphere:-4.54 X 10-2 11' cm' at 600°C, and-4.16 >< 10 fl1 cm1 at 800°C. The effect of BaO excess depends on the concentration of dopant. Compared with BaCe091Y01503_0, doped BaCeO3 with BaO excess (Ba00.90Ce020.025Y203) has a higher total conductivity in all atmospheres studied (02, H2, and wet Ar), whereas the conductivity of BaCeO3 with excess BaO (Ba00.85Ce020.05Y203) is lower than that of BaCe09Y61O26. BaCeO3 based materials have higher conductivities than those of SrCeO2 based materials, whereas SrCeO3 based materials show higher proton transference numbers.
Investigation of protonic conduction in Yb- and Y-doped barium zirconates
Solid State Ionics, 1995
Barium zirconate ceramics doped with Y and Yb, BaM,Zr, _$_ (I (M = Yb, Y), are perovskite single phases and exhibit protonic conduction in moist nitrogen atmospheres at temperatures 500 < T ("C) < 1000. Samples with x = 0.10 have been investigated by ac and dc electrochemical techniques. Conductivities with Yb as dopant were larger, by a factor = 10, than those with Y as dopant. Conductivities for Yb-doped samples (e.g. u,, (750°C) = 2 X 10m4 S cm-') are lower than those reported for analogous cerates. Throughout the experimental temperature range, the apparent conductivity found in dc studies (summing resistances due to the electrolyte and electrode-electrolyte interfacial phenomena) was lower, by a temperature independent factor = 2, than the conductivity determined by ac techniques.
Synthesis, Structure and Proton Conduction of Substituted BaTiO3 and BaZrO3 Perovskites
2013
Proton conducting oxides can be beneficial as electrolyte materials in devices such as fuel cells, hydrogen sensors etc. Proton conducting fuel cells (PCFCs), utilising H 2 as fuel, stand out as a promising technology for future clean energy generation. The works herein is devoted to improve the performance of current state of the art perovskite structured BaZrO 3 based electrolyte materials as well as synthesise and characterise novel electrolytes within the BaTiO 3 based systems. Usually acceptor doping of these perovskites allows for proton conductivity in hydrogen containing atmosphere. In this thesis heavily co-doped strategy along with the impact of addition of sintering aid (ZnO) and various synthesis routes in BaZrO 3 based materials is being tested. Heavily doped BaTiO 3 based systems are also synthesised for the first time and characterised with an emphasis on proton conduction. This work is based on techniques such as X-ray powder diffraction studies, neutron powder diffraction, thermogravimetric analysis and AC impedance spectroscopy. In addition a neutron total scattering study is employed for the first time to understand the local structural environment for the deuteron position in a proton conducting electrolyte. Co-doping and sintering aid (in solution synthesis) for the In/Yb:BaZrO 3 electrolyte seems to be beneficial. Heavily substituted Sc/In:BaTiO 3 materials also show enhanced proton conductivity.
Processing of yttrium-doped barium zirconate for high proton conductivity
Journal of Materials Research, 2007
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, BaZr0.8Y0.2O3−δ 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.
2021
There have been significant developments of solid-state-ion conducting energy materials and perovskite-based oxides those exhibit excellent proton conduction at intermediate temperatures. In contrast to high-temperature oxygen ion-conducting oxides or low-temperature proton-conducting polymers, perovskite oxides have obtained distinguished attention because of their diversified structural aspects and potential applications. Highly stable and conductive electrolytes with improved electrochemical and thermochemical properties are in great demand in numerous fields such as portable electronics and transport systems, energy storage, fuel cells, etc. This review focuses on recent development in the proton-conducting performance of BaZrO 3 (BZO) energy materials. This study aims to integrate the fundamentals of proton conducting BZO perovskites in the prospect of the recent development in materials science and computational engineering. Therefore, in the first half of this review, the bas...
Effects of ZnO addition methods on proton conductivities of barium zirconate modified by ytterbium
Solid State Ionics, 2012
Yb-doped BaZrO 3 samples with relative densities higher than 98% were obtained by the addition of 4 mol% stoichiometric ZnO, excess ZnO, and excess BaZnO 2 , and sintering at 1300°C for 10 h. The stoichiometric addition of ZnO was most effective in obtaining a homogeneous distribution of Zn throughout the grains and grain boundaries. The Yb-doped BaZrO 3 obtained using a stoichiometric addition of ZnO had the cubic perovskite structure, whereas the others had monoclinic perovskite structures. The highest proton conductivity was obtained when ZnO was added stoichiometrically; the conductivity of Yb-doped BaZrO 3 with stoichiometric ZnO and excess ZnO at 500°C was 0.0012 Scm −1 and 0.0004 Scm −1 , respectively. The results are discussed from the viewpoint of the crystal structure and the defect chemistry.
Journal of Materials Research, 1998
The influence of grain boundary conductivity and microstructure on the electrical properties of BaCe0.85Gd0.15O3–δ have been examined. Grain sizes were varied by sintering at various temperatures. Impedance data were analyzed using the brick layer model, and some new consequences of this model are presented. The specific grain boundary conductivity exhibits an activation energy of ~0.7 eV, and for similar processing routes, is independent of grain size. An isotope effect was observed, indicating that protons (or deuterons) are the mobile species. TEM investigations showed the intergranular regions to be free of any glassy phase that could account for the differences in bulk and grain boundary properties. Single-crystal fibers, grown by a modified float zone process, were notably barium deficient, and exhibited a low conductivity, comparable to that of polycrystalline Ba0.96Ce0.85Gd0.15O3–δ.