BaZr0.85Me0.15O2.925 (Me=Y, In and Ga): crystal growth, high-resolution transmission electron microscopy, high-temperature X-ray diffraction and neutron scattering experiments
Introduction
Many perovskite-type ceramics exhibit high-temperature proton conductivity. From the point of applied research, these materials have attracted attention because of their widespread applications as hydrogen sensors [1], [2] and possible applications as proton-conducting electrolytes in solid oxide fuel cells (SOFC) [3], [4], [5], [6].
BaZr0.85Me0.15O2.925 (Me=Y, In and Ga) is known as one of the most outstanding proton-conducting ceramics [7], [8] and is usually prepared as a macrocrystalline material via classical solid-state reaction. As it is now possible to produce nanocrystalline materials in larger amounts and in sufficient quality by a variety of synthesis possibilities, it appears to be a promising approach to combine the superior characteristics of nanoscaled ceramics with the proton-conducting properties of doped perovskites. Additionally, the often drastically different chemical and physical properties of nanoscaled materials in comparison to single crystalline or coarse-grained polycrystalline samples with the same chemical composition are of high interest in materials science.
Section snippets
Preparation
Nanocrystalline powder samples were prepared by a sol–gel type hydrolysis in microemulsion-provided nanoreactors.
The starting materials are metallic barium, a solution of zirconium-tetra-n-propoxide Zr(nOPr)4 in n-propanol (both from Chempur), and a solution of Me-tri-iso-propoxide Me(iOPr)3 (Me=Y, In and Ga) in toluene (Alfa-Aesar). As surfactant, we used Tergitol™ TNP-35 (Sigma-Aldrich), and as cosurfactant, we used analytical grade 1-octanol. As solvents, we used acetone, cyclohexane and
HR-TEM
In Fig. 1a, a typical high-resolution micrograph of a Y3+-doped barium zirconate sample is displayed. The crystallite size can roughly be estimated as between 5 and 10 nm in diameter in agreement with the Scherrer equation which yields 7 nm. The shape is nearly spherical and the particles are agglomerated. Structure imaging enables us to find the cubic phase of BaZrO3 with the interplanar distance values for d(110)≈0.3 nm and d(111)≈0.24 nm as indicated. In Fig. 1b, the results of the EDX line
Conclusion
The microemulsion approach is a suitable method to obtain nanocrystalline materials by applying moderate sintering conditions (30 min at 400°C). HR-TEM shows the crystalline structure of the doped BaZrO3 samples and EDX line scans on the grain boundaries and on the bulk material, and in addition, the neutron scattering experiments prove the enrichment of dopant ions in the grain boundaries. HT-XRD exhibits the significantly reduced crystal growth of all doped samples compared to the pure
Acknowledgements
B.G. thanks IZES and R. Hempelmann for the generous financial support. We acknowledge H. Natter for the HT-XRD measurements. We gratefully acknowledge financial support by the Deutsche Forschungsgemeinschaft within the framework of Sonderforschungsbereich 277 ‘Grenzflächenbestimmte Materialien,’ Universität des Saarlandes and by the German BMBF.
References (14)
- et al.
Solid State Ionics
(1981) - et al.
Solid State Ionics
(1999) Physica B
(1996)- et al.
Solid State Ionics
(1998) - et al.
Solid State Ionics
(1999) Solid State Ionics
(1999)- et al.
Solid State Ionics
(1999)
Cited by (35)
Ionic Conductors and Protonics
2017, Experimental Methods in the Physical SciencesCitation Excerpt :Further examples include the work of Karmonik et al. [110], who investigated the nature of proton dynamics in the double perovskite structured material Ba[Ca0.39Nb0.61]O2.91 which, similarly to the previous studies on SrCe0.95Yb0.05O2.975, gave support for a proton conduction mechanism divided into proton jumps and reorientational motions. Subsequently, Pionke et al. [111] reported on the proton self-diffusion constant for protons in the same material, whereas Groß et al. [112] and Beck et al. [113] investigated the influence of particle size on the atomic-scale proton diffusion in BaZr0.85M0.15O2.925 (M = Y, In, and Ga). An important result was the observation of a clear quasielastic signal in measurements of a microcrystalline sample, whereas measurements on a nanocrystalline equivalent did not manifest any dynamics accessible on the picosecond time-scale as probed by the spectrometer.
Structural properties of Y-doped BaZrO<inf>3</inf> as a function of dopant concentration and position: A density functional study
2013, Solid State IonicsCitation Excerpt :Despite the progress of going inside in the structure–proton conductivity relationship [3–11], there are still several open problems to be overcome in order to meet the requirements for technological applications. The major issues, related with the material preparations, discussed in the literature are associated with the poor sinterability and grain boundary conductivities of acceptor-doped zirconates, including Y-doped BaZrO3 (BZY) [12–18]. Along with the research efforts in developing new synthesis routes, it emerged also the necessity to go deeply insight into the basic issues related with the mechanism of proton conduction in solid-state materials.
Fabrication and electrical characterization of 15% yttrium-doped barium zirconate - Nitrate freeze drying method combined with vacuum heating
2011, Journal of Alloys and CompoundsCitation Excerpt :Therefore, if the particle size of synthesized powder is finer than that of synthesized powder by the solid state reaction method, it is possible to obtain large and homogeneous grains of yttrium-doped barium zirconate in short time because the diffusion distance for cations becomes shorter during sintering at 1600 °C. Among various reports for fabrication of finer oxides [37–40], one unique method, called as the nitrate freeze-drying method, was reported for very fine powder of barium titanate (BaTiO3) (10–15 nm) [40]. In this study, we employed the nitrate freeze-drying method, by which there is no report on the synthesis of barium zirconate, to obtain a fine powder of BaZr0.85Y0.15O3−δ and investigated the sintering behavior and their grain boundary resistances.
Microstructural characterization and electrical properties of spray pyrolyzed conventionally sintered or hot-pressed BaZrO<inf>3</inf> and BaZr <inf>0.9</inf>Y<inf>0.1</inf>O<inf>3 - δ</inf>
2011, Solid State IonicsCitation Excerpt :The ratio between Y and Zr given in Table 2 calculated from the EDS spectra can therefore be compared directly, showing a significantly higher Y concentration at the triple junction (position 2) compared to the bulk material. Segregation of Y also along the grain boundaries cannot be ruled out from the EDS studies, and enrichment of Y along the grain boundaries have been observed by TEM on agglomerated BZY powder by Gross et al. [17]. However, the thickness of any Y-rich separate phase at the grain boundaries in our samples would be below the detectable range of HRTEM.
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Present address: Bayer AG, D-51368 Leverkusen, Germany.