Synthesis and characterisation of novel superconductors

McLennan, Alec
Synthesis and characterisation of novel superconductors. Doctor of Philosophy thesis, University of Liverpool.

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This work presents and discusses the recent advances in high temperature superconductors. It focuses on how both the superconducting fullerides and iron selenides have contributed to the state-of-the-art of high temperature superconductors. The discovery of the relationship between the critical temperature and the proximity of the Cs3C60 material to the Mott metal-insulator transition has clearly demonstrated unconventional superconductivity in fullerides. However, the best samples of Cs3C60 were synthesised in purities of ~80 % which complicates the analysis of the physical properties of this important material. Furthermore, the use of hazardous and dangerous solvents such as methylamine and ammonia limits the availability of these materials for a broader scientific community and therefore, a facile and efficient synthetic procedure would strongly benefit the field. Within this work a novel synthetic method for Cs3C60 in a common THF solvent has been developed producing nearly single phase samples with a critical temperature (Tc) of 33 K. Intercalation of alkali metals into a FeSe host can produce the materials with Tc up to 46 K. However, the structure and composition AxFeySe2 (A=K, Rb and Cs) is under debate. In this work this problem was explored by the creation of a subsolidus KxFeySe2 powder phase diagram at 750oC. This allowed me to identify the existing range for superconducting samples and assess their qualities. It was found that the minority phase with a refined composition of close to K0.5Fe2Se2 and specific cell volume of 209.73 Å3 which is probably responsible for superconductivity. As the high temperature route does not allow the isolation of the superconducting phase in pure form a novel low temperature route has been developed. It involved the reaction of FeSe with potassium acenide reducing agents in THF where the use of the organo-metallic agent was to moderate the reductive capability of potassium. This proof-of-concept method produced superconducting materials with up to with 11 % of superconducting fraction and Tc = 33 K.

Item Type: Thesis (Doctor of Philosophy)
Additional Information: Date: 2013-09 (completed)
Uncontrolled Keywords: Superconductivity, iron selenide, fullerene, alkali metal, powder diffraction
Subjects: ?? QD ??
Depositing User: Symplectic Admin
Date Deposited: 19 Feb 2014 11:05
Last Modified: 16 Dec 2022 04:40
DOI: 10.17638/00014395