A study of structure-property relationships in layered copper oxides

described in Chapter Five. This investigation demonstrates that several intimate structure-compressibility relationships exist in these materials. Chapter Six continues the theme of high pressure crystallography, and examines, in detail, the crystal structure of HgBa sub 2 CuO sub 4 sub + subdelta using high pressure neutron diffraction methods. This study indicates that the pressure induced increase in T sub c observed in HgBa sub 2 CuO sub 4 sub + subdelta, may be related to pressure induced relief of structural strain at the interface between the rock-salt and perovskite type layers of this material. Chapter Seven examines the crystal structure of Hg sub 0 sub . sub 8 Cr sub 0 sub . sub 2 Ba sub 2 CuO sub 4 sub + subdelta under ambient and applied pressure. This study shows that significant distortions arise in the crystal structure of HgBa sub 2 CuO sub 4 sub + subdelta when linear HgO sub 2 units are substituted by tetrahedral CrO sub 4 units. Finally, Chapter Eight describes a simple method for the fabrication of strontium-based mercurocuprate thin films, by pulsed laser ablation. This 'proof of concept' study demonstrates that superconducting, c-axis oriented, thin films of such materials may be fabricated by pulsed laser deposition of a mercury free precursor film, followed by ex-situ annealing of such thin films in the presence of a sacrifical mercury source. In order to better understand the interplay between crystal structure and superconductivity in layered cuprate superconductors, a study of structure-property relationships in a number of layered cuprate materials has been undertaken. These studies are concerned, principally, with the investigation of such structure-property relationships in mercury-based cuprate superconductors. The crystal structure of HgBa sub 2 CuO sub 4 sub + subdelta has been re-examined, on the basis of a conjoint powder X-ray and neutron diffraction study, as described in Chapter Three. This study has determined that, in this material, subtle atomic displacements occur in the neighbourhood of interstitial oxygen atoms. The synthesis, structure and superconducting properties of phases in the (Hg sub 1 sub - sub x Re sub x)Sr sub 2 (Nd sub 1 sub - sub y Ca sub y)Cu sub 2 O sub 6 sub + subdelta system is described in Chapter Four. The superconducting properties of this system may be controlled by judicious manipulation of the chemical stoichiometry. Samples of this system, prepared at room pressure, do not show the enhanced irreversibility field characteristics previously reported for similar materials prepared under high pressure. This difference in behaviour is rationalised in terms of (dis)order of the Hg and Re ions in the (Hg,Re)O subdelta plane of this material. The compressibilities of several layered cuprate materials have been determined using high pressure X-ray diffraction methods, a