A comprehensive understanding of structure and site occupancy of Y in Y-doped BaZrO_3

Y-doped BaZrO_3 (BZY) is of the perovskite structure (ABO_3), and is promising as an electrolyte in protonic ceramic fuel cells (PCFCs). However, factors limiting its protonic conductivity have not been clarified entirely, such as the unclear site occupancy of Y. In this work, X-ray diffraction patterns were collected utilizing synchrotron radiation with an incident energy close to the energy of the Y K absorption edge. Therefore, precise Rietveld refinement was performed to determine the site occupancy of Y by the anomalous dispersion effect. The results revealed that for the stoichiometric sample of BaZr_{0.8}Y_{0.2}O_{3−δ}, Y only occupied the B-site. But in the Ba-deficient sample of Ba_{0.9}Zr_{0.8}Y_{0.2}O_{3−δ}, two perovskite phases with different compositions were observed. In the Y-poor phase, all Y occupied the B-site, while in the other greatly Y-rich and Ba-deficient phase, Y was found to occupy both A and B-sites. These results clearly indicate the tendency towards A-site occupation of Y with an increasing Ba-deficiency

Dopant Site Occupancy and Chemical Expansion in Rare Earth-Doped Barium Zirconate

Rare earth-doped BaZrO[3] is a very attractive material in electrochemical applications due to its proton conductive property. In this work, powder X-ray diffraction patterns of BaZr[0.8]M[0.2]O[3−δ] (M = Sc, Eu, Sm, Dy) were collected using synchrotron radiation, and also using characteristic X-ray of CuKα in dry and wet atmospheres at high temperature. Then, a combined interpretation of the diffraction patterns was established by using Rietveld refinement. The results revealed that an obvious lattice expansion was observed for BaZr[0.8]M[0.2]O[3−δ] (M = Sc, Eu, Sm, Dy) in wet O2compared with the case in dry condition, indicating a chemical expansion effect on lattice volume by incorporating water into lattice. Eu, Sm, and Dy cations occupied both A- and B-sites of BaZrO[3] crystalline lattice, whereas Sc cations were determined to occupy B-site only. These results indicate clearly an increasing tendency toward A-site occupation for the rare earth cations in BaZrO[3] with an increasing radius

Correlation between electroconductive and structural properties of proton conductive acceptor-doped barium zirconate

Various dopants were added to BaZrO[3] and the conductivities, the proton concentrations, the site occupancy of the dopants and the change in lattice volume as a result of chemical expansion were investigated. Lanthanide group dopants occupied both the Ba and Zr sites, but the amount of these dopants in the Ba site was too limited to significantly influence the conductivity. The samples doped with Yb, Tm, Er, Y and Ho showed both high proton concentrations and high conductivities, together with a relatively large lattice expansion as a result of hydration. We therefore suggest that, in most instances, the proton concentration, proton conductivity and lattice change as a result of chemical expansion were all correlated in proton conductive acceptor-doped BaZrO[3]. However, Sc-doped BaZrO[3] seemed to be different. Its proton concentration was high, but the conductivity and lattice change as a result of chemical expansion were relatively small. This indicates that the conductivity was strongly related to the lattice expansion resulting from hydration rather than simply the proton concentration

Effect of grain boundary grooves at the crystal/melt interface on impurity accumulation during the unidirectional growth of multicrystalline silicon

International audienceImpurity accumulation at the grain boundaries in multicrystalline Si (mc-Si) was investigated by in situ observation of the crystal/melt interface, analysis of the grain boundary characteristics, and measurement of impurity concentrations. The impurity concentration was higher at grain boundaries that formed a groove at the crystal/ melt interface than that at regions which did not form a groove at the crystal/melt interface. We conclude that groove formation at the crystal/melt interface is the cause of impurity accumulation at the grain boundary

Effect of an External Electric Field on the Kinetics of Dislocation-Free Growth of Tetragonal Hen Egg White Lysozyme Crystals

Dislocation-free tetragonal hen egg white (HEW) lysozyme crystals were grown from a seed crystal in a cell. The rates of tetragonal HEW lysozyme crystal growth normal to the (110) and (101) faces with and without a 1-MHz external electric field were measured. A decrease in the typical growth rates of the crystal measured under an applied field at 1 MHz was observed, although the overall driving force increased. Assuming that the birth and spread mechanism of two-dimensional nucleation occurs, an increase in the effective surface energy of the step ends was realized in the presence of the electric field, which led to an improvement in the crystal quality of the tetragonal HEW lysozyme crystals. This article also discusses the increase in the effective surface energy of the step ends with respect to the change in the entropy of the solid

Technique for High-Quality Protein Crystal Growth by Control of Subgrain Formation under an External Electric Field

X-ray diffraction (XRD) rocking-curves were measured for tetragonal hen egg white (HEW) lysozyme crystals grown with and without application of an external electric field, and the crystal quality was assessed according to the full width at half-maximums (FWHMs) of each rocking-curve profile. The average FWHMs for tetragonal HEW lysozyme crystals grown with an external electric field at 1 MHz were smaller than those for crystals grown without, especially for the 12 12 0 reflection. The crystal homogeneity of the tetragonal HEW lysozyme crystals was also improved under application of an external electric field at 1 MHz, compared to that without. Improvement of the crystal quality of tetragonal HEW lysozyme crystals grown under an applied field is discussed with a focus on subgrain formation. In addition, the origin of subgrain misorientation is also discussed with respect to the incorporation of impurities into protein crystals

Origins of structural and electrochemical influence on Y-doped BaZrO[3] heat-treated with NiO additive

Nickel (Ni) is expected to be an attractive anode material for protonic ceramic fuel cells using Y-doped BaZrO_3 (BZY) as an electrolyte, since Ni shows good catalytic properties for the anode reaction, and NiO is a sintering aid for BZY. In this work, a systematic investigation has been performed to reveal the influence of Ni incorporation on structural and electrochemical properties of BZY. Then, some new knowledge was obtained; the important point is that Ni cations occupy the interstitial position of (1/2, 0, 0) in the lattice of BZY, with a greatly Ba-deficient environment. As a result, Ba cations were possibly driven to the grain boundary and induced the formation of a liquid phase, which promoted the sintering process. However, the occupation of Ni on this (1/2, 0, 0) position also resulted in a negative influence on conductivity. A careful processing is required to apply Ni as the electrode in BZY based fuel cells