Measurements by Bernhoeft et al [1] of the small-angle neutron scattering in the high-temperature superconductor YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB>-δ showed increased scattering in the vicinity of the superconducting transition temperature of the order of 100-150 mbarns sr<SUP>-1</SUP> atom<SUP>-1</SUP>. This thesis describes further investigations of the temperature dependence of the small-angle neutron scattering from two high-temperature superconductors YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB>-δ and Bi<SUB>2</SUB>Sr<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>8</SUB> where the two predominant problems with these measurements were identified and addressed; namely the large temperature independent 'background' scattering from the superconductor samples, and the drifting of the detector's efficiency. The first part of this thesis is concerned with the preparation, characterisation and preliminary small-angle neutron scattering measurement of YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB>-δ and Bi<SUB>2</SUB>Sr<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>8</SUB> with the small-angle neutron scattering instruments at NIST, U.S.A. and Saclay, France. In these measurements no increase in scattering was observed on the absolute scale of that previously observed [1], the upper limit of scattering being 20-30 mbarns st<SUP>-1</SUP> atom<SUP>-1</SUP> for YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB>-δ and 30 mbarns st<SUP>-1</SUP> atom<SUP>-1</SUP> for Bi<SUB>2</SUB>Sr<SUB>2</SUB>CaCu<SUB>2</SUB>O<SUB>8</SUB>. This however does not rule out the possibility that the small-angle neutron scattering observed at T<SUB>c </SUB>(=90K) at Q=0.035A<SUP>-1</SUP> in reference [1] scales with the background as the percentage change here is of the order of 0.5%±0.1% whereas in the measurements presented in this thesis the change is of the order of 1%±0.2%. Further analysis of the scattering at NIST and measurements made at Saclay, France, showed that for both materials there was considerable variation in the wave-vector dependence of the fractional difference in the differential scattering cross-section when two temperatures were compared.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:599241 |
| Date | January 1995 |
| Creators | Frost, C. D. |
| Publisher | University of Cambridge |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
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