Study of Perovskite and Cuprate Crystallaographic Structures of High Tc Superconductors

Abstract

In this paper, we have studied the perovskite and cuprate crystallographic structure of high Tc super conductors. We know that the majority of single element crystal have highly symmetrical structure, generally fcc or bcc in which their physical properties are the same along the three crystallographic dimensions x, y and z. The NaCl type and A15 compounds are also cubic. Some compounds do have lower symmetric, showing that superconductivity is compitable with many different types of crystallographic structure, but higher symmetric are certainly more common. The structure of high temperature superconductors, almost all of which are tetragonal or orthorhombic. The structure plays very important role in determining the property of superconductors. The higher Tc is alloys of transitions metal are at the boundaries of resistibility between bcc and hep forms. Almost all the high-temperature oxide superconductors have point symmetry D4h ( a = b) or symmetry close to D4h ( a « b). These superconductors consists of horizontal layers, each of which contains one positive ion and either zero, one or two oxygen. The copper ions may be coordinated square planar, pyramidal, or octahedral, with some additional distortion. Copper oxide layers are never adjacent. The captions alternate sites vertically as do the oxygen. The copper oxide layers are either flat or slightly puckered, in contrast to the other metal oxide layers, which are generally far from planar. The highest Tc compounds have metal layers (e.g. Ca) with no oxygen between the Copper Oxide planes.