dc.contributor.authorLi, Henan
dc.contributor.authorBaikie, Tom
dc.contributor.authorPramana, Stevin S.
dc.contributor.authorShin, J. Felix
dc.contributor.authorKeenan, Philip J.
dc.contributor.authorSlater, Peter R.
dc.contributor.authorBrink, Frank
dc.contributor.authorHester, James
dc.contributor.authorAn, Tao
dc.contributor.authorWhite, Timothy John
dc.identifier.citationLi, H., Baikie, T., Pramana, S. S., Shin, J. F., Keenan, P. J., Slater, P. R., et al. (2014). Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases. Inorganic Chemistry, 53(10), 4803-4812.en_US
dc.description.abstractApatite-type oxides ([AI4][AII6][(BO4)6]O2), particularly those of the rare-earth silicate and germanate systems, are among the more promising materials being considered as alternative solid oxide fuel cell electrolytes. Nonstoichiometric lanthanum silicate and germanate apatites display pure ionic conductivities exceeding those of yttria-stabilized zirconia at moderate temperatures (500–700 °C). In this study, mixed Si/Ge-based apatites were prepared by hydrothermal synthesis under mild conditions rather than the conventional solid-state method at high temperatures. Single-phase and highly crystalline nanosized apatite powders were obtained with the morphology changing across the series from spheres for the Si-based end member to hexagonal rods for the Ge-based end member. Powder X-ray and neutron analysis found all of these apatites to be hexagonal (P63/m). Quantitative X-ray microanalysis established the partial (<15 at%) substitution of La3+ by Na+ (introduced from the NaOH hydrothermal reagent), which showed a slight preference to enter the AI 4f framework position over the AII 6h tunnel site. Moreover, retention of hydroxide (OH–) was confirmed by IR spectroscopy and thermogravimetric analysis, and these apatites are best described as oxyhydroxyapatites. To prepare dense pellets for conductivity measurements, both conventional heat treatment and spark plasma sintering methods were compared, with the peculiar features of hydrothermally synthesized apatites and the influence of sodium on the ionic conductivity considered.en_US
dc.description.sponsorshipASTAR (Agency for Sci., Tech. and Research, S’pore)en_US
dc.format.extent36 p.en_US
dc.relation.ispartofseriesInorganic Chemistryen_US
dc.rights© 2014 American Chemical Society. This is the author created version of a work that has been peer reviewed and accepted for publication by Inorganic Chemistry, American Chemical Society. It incorporates referee’s comments but changes resulting from the publishing process, such as copyediting, structural formatting, may not be reflected in this document. The published version is available at: [http://dx.doi.org/10.1021/ic402370e].en_US
dc.subjectSolid oxide fuel cell
dc.subjectHydrothermal synthesis
dc.subjectCrystal chemistry
dc.subjectMicroscopic structure
dc.subjectIonic conductivity
dc.titleHydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phasesen_US
dc.typeJournal Article
dc.contributor.researchEnergy Research Institute @ NTU
dc.contributor.schoolSchool of Materials Science and Engineeringen_US
dc.description.versionAccepted versionen_US

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