The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures
Lead-containing (Pb-B-X)-2H apatites encompass a number of [AF ]4[AT ]6[(BO4)6]X 2 compounds used for waste stabilization, environmental catalysis and ion conduction, but the influence of the stereochemically active lone-pair electrons of Pb2+ on crystal chemistry and functionality is poorly underst...
| Main Authors: | , , , , , , , , , |
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| Format: | Journal Article |
| Language: | English |
| Published: |
2016
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| Online Access: | https://hdl.handle.net/10356/82237 http://hdl.handle.net/10220/39820 |
| _version_ | 1811679005455155200 |
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| author | Baikie, Tom Schreyer, Martin Wei, Fengxia Herrin, Jason Scott Ferraris, Cristiano Brink, Frank Topolska, Justyna Piltz, R. O. Price, Jason White, Timothy John |
| author2 | School of Materials Science & Engineering |
| author_facet | School of Materials Science & Engineering Baikie, Tom Schreyer, Martin Wei, Fengxia Herrin, Jason Scott Ferraris, Cristiano Brink, Frank Topolska, Justyna Piltz, R. O. Price, Jason White, Timothy John |
| author_sort | Baikie, Tom |
| collection | NTU |
| description | Lead-containing (Pb-B-X)-2H apatites encompass a number of [AF ]4[AT ]6[(BO4)6]X 2 compounds used for waste stabilization, environmental catalysis and ion conduction, but the influence of the stereochemically active lone-pair electrons of Pb2+ on crystal chemistry and functionality is poorly understood. This article presents a compilation of existing structural data for Pb apatites that demonstrate paired electrons of Pb2+ at both the AF and AT results in substantial adjustments to the PbFO6 metaprism twist angle, ϕ. New structure refinements are presented for several natural varieties as a function of temperature by single-crystal X-ray diffraction (XRD) of vanadinite-2H (ideally Pb10(VO4)6Cl2), pyromorphite-2H (Pb10(PO4)6Cl2), mimetite-2H/M (Pb10(As5+O4)6Cl2) and finnemanite-2H (Pb10(As3+O3)6Cl2). A supercell for mimetite is confirmed using synchrotron single-crystal XRD. It is suggested the superstructure is necessary to accommodate displacement of the stereochemically active 6s2 lone-pair electrons on the Pb2+ that occupy a volume similar to an O2– anion. We propose that depending on the temperature and concentration of minor substitutional ions, the mimetite superstructure is a structural adaptation common to all Pb-containing apatites and by extension apatite electrolytes, where oxide ion interstitials are found at similar positions to the lone-pair electrons. It is also shown that plumbous apatite framework flexes substantially through adjustments of the Pb F O6 metaprism twist-angles (ϕ) as the temperature changes. Finally, crystal-chemical [100] zoning observed at submicron scales will probably impact on the treatment of diffraction data and may account for certain inconsistencies in reported structures. |
| first_indexed | 2024-10-01T03:02:17Z |
| format | Journal Article |
| id | ntu-10356/82237 |
| institution | Nanyang Technological University |
| language | English |
| last_indexed | 2024-10-01T03:02:17Z |
| publishDate | 2016 |
| record_format | dspace |
| spelling | ntu-10356/822372021-01-08T08:13:00Z The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures Baikie, Tom Schreyer, Martin Wei, Fengxia Herrin, Jason Scott Ferraris, Cristiano Brink, Frank Topolska, Justyna Piltz, R. O. Price, Jason White, Timothy John School of Materials Science & Engineering Earth Observatory of Singapore Energy Research Institute @ NTU (ERI@N) Crystal symmetry; Lone-pair Electrons; PB Apatite Structures; Twist Angles Lead-containing (Pb-B-X)-2H apatites encompass a number of [AF ]4[AT ]6[(BO4)6]X 2 compounds used for waste stabilization, environmental catalysis and ion conduction, but the influence of the stereochemically active lone-pair electrons of Pb2+ on crystal chemistry and functionality is poorly understood. This article presents a compilation of existing structural data for Pb apatites that demonstrate paired electrons of Pb2+ at both the AF and AT results in substantial adjustments to the PbFO6 metaprism twist angle, ϕ. New structure refinements are presented for several natural varieties as a function of temperature by single-crystal X-ray diffraction (XRD) of vanadinite-2H (ideally Pb10(VO4)6Cl2), pyromorphite-2H (Pb10(PO4)6Cl2), mimetite-2H/M (Pb10(As5+O4)6Cl2) and finnemanite-2H (Pb10(As3+O3)6Cl2). A supercell for mimetite is confirmed using synchrotron single-crystal XRD. It is suggested the superstructure is necessary to accommodate displacement of the stereochemically active 6s2 lone-pair electrons on the Pb2+ that occupy a volume similar to an O2– anion. We propose that depending on the temperature and concentration of minor substitutional ions, the mimetite superstructure is a structural adaptation common to all Pb-containing apatites and by extension apatite electrolytes, where oxide ion interstitials are found at similar positions to the lone-pair electrons. It is also shown that plumbous apatite framework flexes substantially through adjustments of the Pb F O6 metaprism twist-angles (ϕ) as the temperature changes. Finally, crystal-chemical [100] zoning observed at submicron scales will probably impact on the treatment of diffraction data and may account for certain inconsistencies in reported structures. ASTAR (Agency for Sci., Tech. and Research, S’pore) MOE (Min. of Education, S’pore) Accepted version 2016-01-29T02:34:38Z 2019-12-06T14:51:28Z 2016-01-29T02:34:38Z 2019-12-06T14:51:28Z 2014 Journal Article Baikie, T., Schreyer, M., Wei, F., Herrin, J. S., Ferraris, C., Brink, F., et al. (2014). The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures. Mineralogical Magazine, 78(2), 325-345. 0026-461X https://hdl.handle.net/10356/82237 http://hdl.handle.net/10220/39820 10.1180/minmag.2014.078.2.07 en Mineralogical Magazine © 2014 The Mineralogical Society. This is the author created version of a work that has been peer reviewed and accepted for publication by Mineralogical Magazine, The Mineralogical 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/10.1180/minmag.2014.078.2.07]. 42 p. application/pdf application/pdf |
| spellingShingle | Crystal symmetry; Lone-pair Electrons; PB Apatite Structures; Twist Angles Baikie, Tom Schreyer, Martin Wei, Fengxia Herrin, Jason Scott Ferraris, Cristiano Brink, Frank Topolska, Justyna Piltz, R. O. Price, Jason White, Timothy John The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures |
| title | The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures |
| title_full | The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures |
| title_fullStr | The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures |
| title_full_unstemmed | The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures |
| title_short | The influence of stereochemically active lone-pair electrons on crystal symmetry and twist angles in lead apatite-2H type structures |
| title_sort | influence of stereochemically active lone pair electrons on crystal symmetry and twist angles in lead apatite 2h type structures |
| topic | Crystal symmetry; Lone-pair Electrons; PB Apatite Structures; Twist Angles |
| url | https://hdl.handle.net/10356/82237 http://hdl.handle.net/10220/39820 |
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