The atomistic modelling approach to designing new metal-boride superconductors
<p>A series of metal-boride compounds have been studied using density functional theory with the goal of discovering and designing new superconductors with the highest possible superconducting critical temperature (T<sub>c</sub>). The materials design process involves predicting cr...
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| Format: | Thesis |
| Language: | English |
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2013
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| _version_ | 1797065416684601344 |
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| author | Shah, S |
| author2 | Kolmogorov, A |
| author_facet | Kolmogorov, A Shah, S |
| author_sort | Shah, S |
| collection | OXFORD |
| description | <p>A series of metal-boride compounds have been studied using density functional theory with the goal of discovering and designing new superconductors with the highest possible superconducting critical temperature (T<sub>c</sub>). The materials design process involves predicting crystal structures using an evolutionary algorithm followed by the calculation of the T<sub>c</sub> for any metallic structures using the Migdal-Eliashberg theory. The reasons for superconductivity are rationalised through examining the electronic and vibrational features of the system. Finally, the stability of metal-boride compounds is studied to find hints to speed up the superconductor design process.</p><p>An ambient pressure, ground state structure of oP10-FeB is proposed as being one of the rare iron-based BCS-type superconductors, with a T<sub>c</sub> of 15-20 K. Unlike MgB where the Fermi level is composed of boron electronic states, here 2/3 of the states at the Fermi level originate from the iron atom and only 1/3 from the boron atom. An extensive study has been done to show that the structure is neither ferro- nor antiferromagnetic. CrB is also predicted to form same oP10 structure as FeB but is not expected to be superconducting. Experiments have recently confirmed the predicted oP10 FeB and CrB structures, with superconductivity being observed in FeB.</p><p>The whole Ca<sub>x</sub>B<sub>1-x</sub> composition range has been studied at ambient and gigapascal pressures, proposing stable high pressure superconducting compounds for CaB, CaB and CaB<sub>6.125</sub>. The highest T<sub>c</sub> predicted is 5 K for CaB at 30 GPa. The rest of the compounds have T<sub>c</sub>'s on the order of 1 K showing that whilst may be possible to predict very stable structures, this is not so good for discovering a superconductor with a high T<sub>c</sub>. Stable high pressure forms of CaB and CaB are also discussed where their pressure induced crystallographic phase transitions are explained through comparing with alkaline earth analogues. The stability of a particular boron network at any pressure is shown to be heavily dependent on the metallic ion size.</p> |
| first_indexed | 2024-03-06T21:28:22Z |
| format | Thesis |
| id | oxford-uuid:43da6437-275b-4087-aaca-eea3e490b5ab |
| institution | University of Oxford |
| language | English |
| last_indexed | 2024-03-06T21:28:22Z |
| publishDate | 2013 |
| record_format | dspace |
| spelling | oxford-uuid:43da6437-275b-4087-aaca-eea3e490b5ab2022-03-26T14:58:00ZThe atomistic modelling approach to designing new metal-boride superconductorsThesishttp://purl.org/coar/resource_type/c_db06uuid:43da6437-275b-4087-aaca-eea3e490b5abAtomic scale structure and propertiesMaterials modellingCondensed Matter PhysicsEnglish2013Shah, SKolmogorov, A<p>A series of metal-boride compounds have been studied using density functional theory with the goal of discovering and designing new superconductors with the highest possible superconducting critical temperature (T<sub>c</sub>). The materials design process involves predicting crystal structures using an evolutionary algorithm followed by the calculation of the T<sub>c</sub> for any metallic structures using the Migdal-Eliashberg theory. The reasons for superconductivity are rationalised through examining the electronic and vibrational features of the system. Finally, the stability of metal-boride compounds is studied to find hints to speed up the superconductor design process.</p><p>An ambient pressure, ground state structure of oP10-FeB is proposed as being one of the rare iron-based BCS-type superconductors, with a T<sub>c</sub> of 15-20 K. Unlike MgB where the Fermi level is composed of boron electronic states, here 2/3 of the states at the Fermi level originate from the iron atom and only 1/3 from the boron atom. An extensive study has been done to show that the structure is neither ferro- nor antiferromagnetic. CrB is also predicted to form same oP10 structure as FeB but is not expected to be superconducting. Experiments have recently confirmed the predicted oP10 FeB and CrB structures, with superconductivity being observed in FeB.</p><p>The whole Ca<sub>x</sub>B<sub>1-x</sub> composition range has been studied at ambient and gigapascal pressures, proposing stable high pressure superconducting compounds for CaB, CaB and CaB<sub>6.125</sub>. The highest T<sub>c</sub> predicted is 5 K for CaB at 30 GPa. The rest of the compounds have T<sub>c</sub>'s on the order of 1 K showing that whilst may be possible to predict very stable structures, this is not so good for discovering a superconductor with a high T<sub>c</sub>. Stable high pressure forms of CaB and CaB are also discussed where their pressure induced crystallographic phase transitions are explained through comparing with alkaline earth analogues. The stability of a particular boron network at any pressure is shown to be heavily dependent on the metallic ion size.</p> |
| spellingShingle | Atomic scale structure and properties Materials modelling Condensed Matter Physics Shah, S The atomistic modelling approach to designing new metal-boride superconductors |
| title | The atomistic modelling approach to designing new metal-boride superconductors |
| title_full | The atomistic modelling approach to designing new metal-boride superconductors |
| title_fullStr | The atomistic modelling approach to designing new metal-boride superconductors |
| title_full_unstemmed | The atomistic modelling approach to designing new metal-boride superconductors |
| title_short | The atomistic modelling approach to designing new metal-boride superconductors |
| title_sort | atomistic modelling approach to designing new metal boride superconductors |
| topic | Atomic scale structure and properties Materials modelling Condensed Matter Physics |
| work_keys_str_mv | AT shahs theatomisticmodellingapproachtodesigningnewmetalboridesuperconductors AT shahs atomisticmodellingapproachtodesigningnewmetalboridesuperconductors |