Studies of systems related to high-Tc superconductors by electron microscopy and X-ray powder diffraction

Sammanfattning: New cuprate systems related to high temperature superconductors have been investigated and are reviewed. The synthesized samples have been studied mainly by transmission electron microscopy, energy-dispersive spectrometry and X-ray powder diffraction, in order to determine composition and structure of the formed phases.The following compounds were studied: Bi14Cu10Nb16O7 and Bit 7Cuo.2Ti2.006.8, both of cubic pyrochlore-type structure; BiNbs.4015, a tetragonal tungsten bronze type compound; Bi2/3Cu3Ti4012, a perovskite-related phase; Ba4CuYW2012, with a perovskite based unit cell; LaSrCuGaOs and LaCaCuGaOs, both of brownmillerite type and some related phases obtained by aliovalent substitution; R2Hg04 (R = La, Nd, Sm, Eu and Gd), with a new type of structure; and HgBa^RCugOy (R = La, Nd, Eu, Eu+Ca, Gd, Dy and Y), new "Hg-1212" type phases with a structure related to that of the thallium superconductor TlBa2CaCu207.The structural features of these compounds of relevance to superconductivity are also discussed.