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Structure-property relations in non-cuprate superconductors

Green, Mark A.; (1995) Structure-property relations in non-cuprate superconductors. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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Abstract

The vibrational properties of (Ba,K)BiO3 are studied in the semi-conducting, metallic and superconducting regimes by Raman and inelastic neutron scattering techniques. Mode assignment is achieved with the aid of interatomic potential calculations. The oxygen phonon modes are found to be sensitive to changes in composition, oxidation state of the Bi ions, as well as temperature, which are ascribed to strong electron- phonon coupling and discussed within the context of the BCS theory. Novel behaviour in the LO oxygen bending mode as a function of K doping is proposed to arise from the occurrence of structural phase transitions in this system. Rietveld refinement of powder neutron diffraction data has confirmed the Fd 3 m spinel structure throughout the range of lithium doping in Li1+xTi2-xO4- Inelastic neutron scattering and interatomic potential calculations are employed in the investigation of the vibrational properties. Although no temperature effects were observed, strong changes are seen when comparing LiTi2O4 with insulating Li4Ti5O12, giving evidence for the existence of electron-phonon coupling and a BCS-like phonon mediated mechanism for superconductivity. The structure and vibrational properties of Ba(Sn,Sb)O3 system, analogous to superconducting Ba(Pb,Bi)O3, is studied by neutron elastic and inelastic scattering. Structural phase transitions or strong changes in the phonon spectra, found for LiTi2O4 and (Ba,K)BiO3, are not observed, giving insight for the existence of metallic but not superconducting properties. The structure of various layered and three dimensional members of the Ruddlesdon-Popper homologous series, (Ba,Sr)n+1SnnO3n+1 are solved by Rietveld refinement of powder neutron diffraction data. Powder neutron diffraction and SQUID measurements are employed in the study of the spin-Peierls system, GeCuO3. Rietveld refinement was performed with anisotropic broadening of the [h01] reflections for all three temperature data sets; 300 K, 20 K and 4.2 K. Relaxation of the strain parameters is seen through Tsp.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Structure-property relations in non-cuprate superconductors
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQueset
Keywords: Pure sciences; Superconductors
URI: https://discovery.ucl.ac.uk/id/eprint/10101500
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