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Title: X-ray scattering studies of CDW modulated structures in Ba1-xKxBiO3
Author: Du, Chao-Hung
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 1996
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The correlation between charge-density waves (CDWs) and superconductivity has been a subject of extensive study for a long time. This thesis describes a series of x-ray scattering experiments designed to study CDWs in perovskite superconductors. A review of the properties of CDW materials and the relationship between CDWs and superconductivity is given. Using x-ray scattering techniques the modulated structures caused by the formation of a CDW state have been clarified in a variety of single crystals of Ba1-xKxBiO3. In low resolution measurements, the CDW satellites produce a superstructure doubling the unit cell existing in the range from the semiconducting state (00.37), even in the low temperature superconducting state. Additional peaks with G2 = 0.33a* were observed, which are only present in semiconducting samples. An attempt to determine the size of the modulated structure was undertaken using higher resolution x-ray scattering in the superconductor Ba0.6K0.4BiO3. In this study, the modulated structure was identified to be incommensurate with the host lattice with G1=0.494a* ± 0.11b* and a rather short correlation length of ˜150Å limited by the CDW domain size. An unusual decrease in the intensities of the CDW superlattice reflections was also observed as the temperature was lowered. Evidence to support to the attribution of these satellites to a CDW distortion was obtained from measurements conducted under applied magnetic fields. Increased splitting of the CDW satellites was observed under a magnetic field of 0.8 T with an extremely long relaxation time when the field was removed. Such a long relaxation time is a characteristic of CDWs associated with metastable states.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available