Soft chemical control of layered oxychalcogenides
<p>The structure, magnetic behaviour and chemistry of layered oxychalcogenides of composition <em>A</em><sub>2</sub><em>M</em>O<sub>2</sub><em>X</em><sub>2</sub><em>Ch</em><sub>2</sub> (where A = Sr...
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| Format: | Thesis |
| Language: | English |
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2017
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| _version_ | 1826315643175043072 |
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| author | Blandy, J |
| author2 | Clarke, S |
| author_facet | Clarke, S Blandy, J |
| author_sort | Blandy, J |
| collection | OXFORD |
| description | <p>The structure, magnetic behaviour and chemistry of layered oxychalcogenides of composition <em>A</em><sub>2</sub><em>M</em>O<sub>2</sub><em>X</em><sub>2</sub><em>Ch</em><sub>2</sub> (where A = Sr, Ba; M = Mn, Co, Ni, Cu, Zn; X = Cu, Ag and <em>Ch</em> = S, Se, Te) has been investigated by the synthesis of new compounds of this type and control of the properties of these compounds by oxidative deintercalation of Cu/Ag.</p> <p>I<sub>2</sub> can be used to oxidatively deintercalate Cu from Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>1.5</sub>S<sub>2</sub>, forming Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>1.33</sub>S<sub>2</sub>, an incommensurately modulated compound, with a completely different Cu/vacancy ordering and antiferromagnetic ordering structure to the parent. This reaction is also probed in real-time, using <em>in situ</em> powder X-ray diffraction.</p> <p>Sr<sub>2</sub>MnO<sub>2</sub>Ag<sub>1.5</sub>Se<sub>2</sub> was found to have an <em>A</em>-type magnetic ordering structure, similar to Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>1.5</sub>Se<sub>2</sub>. Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>1.8</sub>Te<sub>2</sub> on the other hand with a lower Mn oxidation state shows only two-dimensional magnetic correlations, rather than long-range order.</p> <p>Extending the reaction with I<sub>2</sub> to several Co-containing analogues revealed that &Tilde; 25% Ag could be removed from Sr<sub>2</sub>CoO<sub>2</sub>Ag<sub>2</sub>Se<sub>2</sub>, sufficient to observe a change in magnetic behaviour, from antiferromagnetic to ferromagnetic. By contrast only &Tilde;11% Cu can be deintercalated from Sr<sub>2</sub>CoO<sub>2</sub>Cu<sub>2</sub>S<sub>2</sub> and even less (&Tilde;5%) from Sr<sub>2</sub>CoO<sub>2</sub>Cu<sub>2</sub>Se<sub>2</sub>. Neutron diffraction was used to examine the resultant changes in magnetic ordering.</p> <p>The novel compounds Sr<sub>2</sub>CuO<sub>2</sub>Cu<sub>2</sub>Se<sub>2</sub> and Ba<sub>2</sub>CuO<sub>2-x</sub>Cu<sub>2</sub>Se<sub>2</sub> are related by substitution of the alkali-earth metal, but while Sr<sub>2</sub>CuO<sub>2</sub>Cu<sub>2</sub>Se<sub>2</sub> is a stoichiometric compound with metal-like character, Ba<sub>2</sub>CuO<sub>2-x</sub>Cu<sub>2</sub>Se<sub>2</sub> is an oxygen-deficient semiconductor, with tuneable oxygen content.</p> <p>Unusual features are observed in the magnetic susceptibility measurements of Sr<sub>2</sub>NiO<sub>2</sub>Cu<sub>2</sub>Se<sub>2</sub> that appear unrelated to this compound's long-range magnetic ordering, as probed by neutron diffraction. Furthermore, unusual peak splitting is observed in low-temperature powder X-ray diffraction patterns of this compound; this may plausibly be due to a photon-induced effect arising from the use of a high-energy beamline; although further measurements are required to examine this.</p> <p>Overall the work shows the flexibility and range of behaviour exhibited by a series of the transition metal oxide chalcogenides.</p> |
| first_indexed | 2024-03-06T18:49:41Z |
| format | Thesis |
| id | oxford-uuid:0fcc2604-0e0d-4206-a0aa-3fdcc611e357 |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-12-09T03:29:52Z |
| publishDate | 2017 |
| record_format | dspace |
| spelling | oxford-uuid:0fcc2604-0e0d-4206-a0aa-3fdcc611e3572024-12-01T12:35:15ZSoft chemical control of layered oxychalcogenidesThesishttp://purl.org/coar/resource_type/c_db06uuid:0fcc2604-0e0d-4206-a0aa-3fdcc611e357Chemistry, InorganicEnglishORA Deposit2017Blandy, JClarke, S<p>The structure, magnetic behaviour and chemistry of layered oxychalcogenides of composition <em>A</em><sub>2</sub><em>M</em>O<sub>2</sub><em>X</em><sub>2</sub><em>Ch</em><sub>2</sub> (where A = Sr, Ba; M = Mn, Co, Ni, Cu, Zn; X = Cu, Ag and <em>Ch</em> = S, Se, Te) has been investigated by the synthesis of new compounds of this type and control of the properties of these compounds by oxidative deintercalation of Cu/Ag.</p> <p>I<sub>2</sub> can be used to oxidatively deintercalate Cu from Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>1.5</sub>S<sub>2</sub>, forming Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>1.33</sub>S<sub>2</sub>, an incommensurately modulated compound, with a completely different Cu/vacancy ordering and antiferromagnetic ordering structure to the parent. This reaction is also probed in real-time, using <em>in situ</em> powder X-ray diffraction.</p> <p>Sr<sub>2</sub>MnO<sub>2</sub>Ag<sub>1.5</sub>Se<sub>2</sub> was found to have an <em>A</em>-type magnetic ordering structure, similar to Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>1.5</sub>Se<sub>2</sub>. Sr<sub>2</sub>MnO<sub>2</sub>Cu<sub>1.8</sub>Te<sub>2</sub> on the other hand with a lower Mn oxidation state shows only two-dimensional magnetic correlations, rather than long-range order.</p> <p>Extending the reaction with I<sub>2</sub> to several Co-containing analogues revealed that &Tilde; 25% Ag could be removed from Sr<sub>2</sub>CoO<sub>2</sub>Ag<sub>2</sub>Se<sub>2</sub>, sufficient to observe a change in magnetic behaviour, from antiferromagnetic to ferromagnetic. By contrast only &Tilde;11% Cu can be deintercalated from Sr<sub>2</sub>CoO<sub>2</sub>Cu<sub>2</sub>S<sub>2</sub> and even less (&Tilde;5%) from Sr<sub>2</sub>CoO<sub>2</sub>Cu<sub>2</sub>Se<sub>2</sub>. Neutron diffraction was used to examine the resultant changes in magnetic ordering.</p> <p>The novel compounds Sr<sub>2</sub>CuO<sub>2</sub>Cu<sub>2</sub>Se<sub>2</sub> and Ba<sub>2</sub>CuO<sub>2-x</sub>Cu<sub>2</sub>Se<sub>2</sub> are related by substitution of the alkali-earth metal, but while Sr<sub>2</sub>CuO<sub>2</sub>Cu<sub>2</sub>Se<sub>2</sub> is a stoichiometric compound with metal-like character, Ba<sub>2</sub>CuO<sub>2-x</sub>Cu<sub>2</sub>Se<sub>2</sub> is an oxygen-deficient semiconductor, with tuneable oxygen content.</p> <p>Unusual features are observed in the magnetic susceptibility measurements of Sr<sub>2</sub>NiO<sub>2</sub>Cu<sub>2</sub>Se<sub>2</sub> that appear unrelated to this compound's long-range magnetic ordering, as probed by neutron diffraction. Furthermore, unusual peak splitting is observed in low-temperature powder X-ray diffraction patterns of this compound; this may plausibly be due to a photon-induced effect arising from the use of a high-energy beamline; although further measurements are required to examine this.</p> <p>Overall the work shows the flexibility and range of behaviour exhibited by a series of the transition metal oxide chalcogenides.</p> |
| spellingShingle | Chemistry, Inorganic Blandy, J Soft chemical control of layered oxychalcogenides |
| title | Soft chemical control of layered oxychalcogenides |
| title_full | Soft chemical control of layered oxychalcogenides |
| title_fullStr | Soft chemical control of layered oxychalcogenides |
| title_full_unstemmed | Soft chemical control of layered oxychalcogenides |
| title_short | Soft chemical control of layered oxychalcogenides |
| title_sort | soft chemical control of layered oxychalcogenides |
| topic | Chemistry, Inorganic |
| work_keys_str_mv | AT blandyj softchemicalcontroloflayeredoxychalcogenides |