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We report a detailed neutron diffraction study of both pinned and moving magnetic Flux Line Lattice (FLL) in NbTa and PbIn samples. In NbTa, the FLL presents a hexagonal lattice even in the absence of current, meanwhile PbIn presents a strongly dislocated phase. In PbIn, dislocations are eliminated by the application of transport current in agreement with theoretical predictions. On the other hand, the absence of curvature of the flux lines for subcritical currents confirm the presence of surface pinning of the FLL.

The relationship between carrier concentration, structure and composition in Bi 2 Sr 2 CaCu 2 O 8+ δ is amongst the most complex of the high- T c superconducting cuprates. In this paper a number of structural subtleties of the system are discussed based on the results of high-resolution X-ray scattering measurements from single crystals. It is found that the annealing of an oxygen-rich crystal significantly changes the character of certain diffuse scattering features. Accompanying analysis of composition and measurements of T c suggest these changes may be the signature of oxygen ordering which is influential to the superconductivity.

The properties of the incommensurate modulation of Bi-2212 have been investigated using X-ray scattering to observe in situ the response of the structure to high temperature (up to 450°C). The results demonstrate the temperature independent nature of the incommensurability, and several pinning mechanisms which would offer explanations for this are discussed. The strong influence exerted by oxygen diffusion over the structure is also highlighted, and the results clearly indicate the existence of two distinct oxygen diffusion processes. However, it is also found that the wavevector of the modulation is in no way a continuous function of oxygen content; a result contrary to the widespread assumptions in the literature. Only after prolonged annealing was evidence for a structural transition observed, involving the appearance of reflections with an apparently new wavevector of q ≈ 0.14 b ∗ + c ∗ .