Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases
Apatite-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...
| Main Authors: | , , , , , , , , , |
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| Format: | Journal Article |
| Language: | English |
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2016
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| Online Access: | https://hdl.handle.net/10356/84929 http://hdl.handle.net/10220/39815 |
| _version_ | 1824456689165795328 |
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| author | Li, Henan Baikie, Tom Pramana, Stevin S. Shin, J. Felix Keenan, Philip J. Slater, Peter R. Brink, Frank Hester, James An, Tao White, Timothy John |
| author2 | School of Materials Science & Engineering |
| author_facet | School of Materials Science & Engineering Li, Henan Baikie, Tom Pramana, Stevin S. Shin, J. Felix Keenan, Philip J. Slater, Peter R. Brink, Frank Hester, James An, Tao White, Timothy John |
| author_sort | Li, Henan |
| collection | NTU |
| description | Apatite-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. |
| first_indexed | 2025-02-19T03:58:05Z |
| format | Journal Article |
| id | ntu-10356/84929 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2025-02-19T03:58:05Z |
| publishDate | 2016 |
| record_format | dspace |
| spelling | ntu-10356/849292023-07-14T15:49:25Z Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases Li, Henan Baikie, Tom Pramana, Stevin S. Shin, J. Felix Keenan, Philip J. Slater, Peter R. Brink, Frank Hester, James An, Tao White, Timothy John School of Materials Science & Engineering Energy Research Institute @ NTU (ERI@N) Electrolyte Ionic conductivity Apatite Solid oxide fuel cell Hydrothermal synthesis Crystal chemistry Microscopic structure Apatite-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. ASTAR (Agency for Sci., Tech. and Research, S’pore) Accepted version 2016-01-26T08:55:26Z 2019-12-06T15:53:49Z 2016-01-26T08:55:26Z 2019-12-06T15:53:49Z 2014 Journal Article Li, 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. 0020-1669 https://hdl.handle.net/10356/84929 http://hdl.handle.net/10220/39815 10.1021/ic402370e en Inorganic Chemistry © 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]. 36 p. application/pdf |
| spellingShingle | Electrolyte Ionic conductivity Apatite Solid oxide fuel cell Hydrothermal synthesis Crystal chemistry Microscopic structure Li, Henan Baikie, Tom Pramana, Stevin S. Shin, J. Felix Keenan, Philip J. Slater, Peter R. Brink, Frank Hester, James An, Tao White, Timothy John Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases |
| title | Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases |
| title_full | Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases |
| title_fullStr | Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases |
| title_full_unstemmed | Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases |
| title_short | Hydrothermal Synthesis, Structure Investigation, and Oxide Ion Conductivity of Mixed Si/Ge-Based Apatite-Type Phases |
| title_sort | hydrothermal synthesis structure investigation and oxide ion conductivity of mixed si ge based apatite type phases |
| topic | Electrolyte Ionic conductivity Apatite Solid oxide fuel cell Hydrothermal synthesis Crystal chemistry Microscopic structure |
| url | https://hdl.handle.net/10356/84929 http://hdl.handle.net/10220/39815 |
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