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| Author(s): |
Ausdinir Danilo Bortolozo
Total Authors: 1
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| Document type: | Doctoral Thesis |
| Press: | Lorena. |
| Institution: | Universidade de São Paulo (USP). Escola de Engenharia de Lorena (EEL/ASDI) |
| Defense date: | 2009-04-09 |
| Examining board members: |
Carlos Alberto Moreira dos Santos;
Enzo Granato;
Renato de Figueiredo Jardim;
Cristina Bórmio Nunes;
Durval Rodrigues Junior
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| Advisor: | Antonio Jefferson da Silva Machado |
| Abstract | |
In this work a study about the investigation of carbide superconductors is shown. These compounds are reported to be hexagonal with space group P63/mmc which are isomorphs to the Cr2AlC compound so called Nowotny phases. These materials have common chemical formula M2AX where M is a transition metal, A an A-group element, and X is C and/or N. In this work the Ti-In-C, Ti-In-N, Nb-Sn-C, Nb-In-C, Ti-Ge-C and Nb-Ge-C systems are investigated. The results concerning all systems show that M2AX phase are superconductors and the superconducting critical temperature depends on the transition metal element. The results suggest that the superconductivity occurs in the layers where MX atoms are chemically bonded. This fact suggests anisotropy in these systems which are in agreement with band structure calculations. It will be also shown the discovery of a new phase belonging to the M2AX family with Nb2GeC composition which crystallizes in the Cr2AlC prototype. Careful analyses of the Nb-Ge-C system also show the discovery of a new superconductor of Nb5Ge3Cx composition as an interstitial carbide compound. The temperature dependence for both electrical resistivity and diamagnetism data demonstrated bulk type II superconductivity below 15.3 K. These phases crystallize in the Mn5Si3 prototype which are also called Nowotny phases. On the other hand the boron substitution is also able to induce superconducting behavior. Finally, the results reported in this work show clearly a new superconducting family with hexagonal structure, which crystallizes in the Cr2AlC prototype and a possible new interstitial family which crystallizes in the Mn5Si3 prototype. (AU) | |