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J.?R.?Tolchard J.?E.?H.?Sansom P.?R.?SlaterEmail author M.?S.?Islam 《Journal of Solid State Electrochemistry》2004,8(9):668-673
Recently, high oxide ion conduction has been observed in the apatite-type systems La9.33+x(Si/Ge)6O26+x/2, with conductivities approaching and even exceeding that of yttria-stabilized zirconia. The Ge-based phases have been reported to suffer from Ge loss and undergo irreversible structural changes on sintering at the high temperatures required to obtain dense pellets. In this paper we discuss doping studies (Ba, Bi for La) aimed at stabilizing the hexagonal apatite lattice to high temperature, and/or lowering the synthesis and sintering temperatures. The results show that doping with Ba helps to stabilize the hexagonal lattice at high temperatures, although Ge loss appears to still be a problem. Conductivity data show that, as previously reported for the Si-based systems, non-stoichiometry in the form of cation vacancies and/or oxygen excess is required to achieve high oxide ion conduction in these Ge-based systems. Neutron diffraction structural data for the fully stoichiometric phase La8Ba2Ge6O26 shows that the channel oxygen atoms show little anisotropy in their thermal displacement parameters, consistent with the low oxide ion conductivity of this phase. Bi doping is shown to lower the synthesis and sintering temperatures, although the presence of Bi means that these samples are not stable at high temperatures under reducing conditions.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, April 10–12, 2003 相似文献
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Tolchard JR Sansom JE Islam MS Slater PR 《Dalton transactions (Cambridge, England : 2003)》2005,(7):1273-1280
A series of Co doped lanthanum silicate apatite-type phases, La9.83Si4.5Co1.5O26, La9.66Si5CoO26, La10Si5CoO26.5 and La8BaCoSi6O26, have been synthesised, and neutron diffraction, EXAFS and XANES used to investigate their structures in detail. All compositions were shown to possess the hexagonal apatite structure, and the results confirmed that cobalt can be doped onto both the La and Si sites within the structure depending on the starting composition. The Co doping is shown to cause considerable local distortions within the apatite structure. In the case of Si site doping two compositions showed anisotropic peak broadening, which has been attributed to incommensurate ordering of oxygen within the apatite channels. 相似文献
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Bond PJ Cuthbertson JM Deol SS Sansom MS 《Journal of the American Chemical Society》2004,126(49):15948-15949
The in vitro study of membrane proteins for the purpose of physicochemical analysis or structure determination often relies upon successful reconstitution into detergent micelles. Moreover, a number of biological processes such as membrane protein folding and transport rely on lipid interactions which may resemble the micellar environment. Little is known about the structures of these micelles or the processes which lead to their formation. We therefore present two 50 ns all-atom molecular dynamics simulations of spontaneous dodecylphosphocholine micelle formation around representatives of the two major families of membrane proteins, a small beta-barrel protein, OmpA, and a model alpha-helical protein, glycophorin A. Despite differences in protein architecture, we highlight common mechanistic pathways in micelle formation, which are consistent with experimental studies. We characterize the exponential kinetics of detergent-protein adsorption and suggest a simple model which may explain the aggregation process. We also compare the results with 25 and 50 ns simulations of preformed micelles containing the same proteins. We confirm that the end structures of the self-assembled micelles are similar to those from their preformed counterparts, with each micelle presenting a bilayerlike environment to the enclosed protein. 相似文献
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Synthesis and conductivities of the apatite-type systems, La9.33+xSi6−yMyO26+z (M=Co, Fe, Mn) and La8Mn2Si6O26 总被引:1,自引:1,他引:0
Apatite-type oxides of formula (La/Sr)10−xSi6O26+y have been attracting significant interest recently, because of their high oxide ion conductivity. In this paper we report
the synthesis and conductivities of phases based on doping La9.33Si6O26 with Co, Fe, Mn on the Si site, according to the formula La9.33+x/3Si6−xMxO26 (M=Co, Fe, Mn). Substitution limits observed were x≤1.5 (Co), x≤1.25 (Fe), x≤0.5 (Mn). Higher Mn levels could be achieved
by substituting onto the La site, with it being possible to prepare the phase La8Mn2Si6O26. The highest conductivities were observed for the Co doped samples, although investigations into the dependence of conductivity
on p(O2) (0.2–10−5 atm.) indicated that the conductivity was dominated by the electronic component in these cases. In contrast, the conductivities
for the Fe and Mn doped samples were mainly ionic in the same p(O2) range. Experiments into varying the oxygen content of these doped phases indicated that increasing the oxygen content above
the nominally stoichiometric O26 appears to increase the oxide ion conductivity.
Preliminary studies of the reactivity of the electrolyte La9.33Si6O26 with potential SOFC cathode materials (La1−xSrxMO3; M=Co, Fe, Mn) suggests that reaction can occur at high temperatures leading to the incorporation of the transition metal
into the apatite electrolyte. However, the fact that these doped phases exhibit high conductivities suggests that this may
limit any problems caused by such a reaction at the electrolyte-electrode interface.
Paper presented at the 8th EuroConference on Ionics, Carvoeiro, Algarve, Portugal, Sept. 16–22, 2001. 相似文献
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Octyl glucoside (OG) is a detergent widely employed in structural and functional studies of membrane proteins. To better understand the nature of protein-OG interactions, molecular dynamics simulations (duration 10 ns) have been used to explore an alpha-helical membrane protein, GlpF, in OG micelles and in DMPC bilayers. Greater conformational drift of the extramembraneous protein loops, from the initial X-ray structure, is seen for the GlpF-OG simulations than for the GlpF-DMPC simulation. The mobility of the transmembrane alpha-helices is approximately 1.3x higher in the GlpF-OG than the GlpF-DMPC simulations. The detergent is seen to form an irregular torus around the protein. The presence of the protein leads to a small perturbation in the behavior of the alkyl chains in the OG micelle, namely an approximately 15% increase in the trans-gauche(-)-gauche(+) transition time. Aromatic side chains (Trp, Tyr) and basic side chains (Arg, Lys) play an important role in both protein-detergent (OG) and protein-lipid (DMPC) interactions. 相似文献
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A comparison of the effect of rare earth vs Si site doping on the conductivities of apatite-type rare earth silicates 总被引:1,自引:0,他引:1
J. E. H. Sansom E. Kendrick J. R. Tolchard M. S. Islam P. R. Slater 《Journal of Solid State Electrochemistry》2006,10(8):562-568
Apatite-type lanthanum silicate (La9.33Si6O26) has been attracting significant recent interest due to its high oxide ion conductivity. In this paper, synthesis and conductivity
data for a range of doped samples (Mg, Ca, Sr, Ba, B, Ga and Zn) are reported, in particular, to compare the effect of rare
earth vs Si site doping. The results show that Ga, B and Zn favour substitution on the Si site, while Ca, Sr and Ba favour
La-site substitution. Mg is shown to be an ambi-site dopant, substituting on either site depending on the starting composition.
The samples doped on the Si site show higher conductivities than comparable samples doped on the La site, providing further
support for the importance of the silicate network in the conduction process, as initially predicted by atomistic modelling
studies. For Ga doping on the Si site, the effect of varying the rare-earth size on the conductivities is also reported. 相似文献