Two interesting topics of layered high-Tc copper oxides, Tl and Pb systems investigated recently in our laboratory are presented to get better understanding of the chemistry and superconductivity of these peculiar compounds. First, a comparative study of double and single Tl layer oxides has been done. The most probable explanation for the origin of holes responsible for a high Tc above 100 K in the double Tl layer oxides is electron transfer mechanism Tl3-t-Cu2+2t/n. Evidence for a reduced state in Tl ions is obtained by XPS and XANES measurements. Single Tl layer oxides are shown to be more ionic by XPS and NMR measurements. The block layer of Pb(Ba,Sr)2YCu3O7 lacks one PbO layer from the PbO-Cu-PbO block layer as revealed by high-resolution electron microscopy. In the (Pb,Cu) double layer oxides, an abrupt oxygen removal and uptake accompanied by phase transition was observed to occur in a reversible fashion. Pb(Ba,Sr)2YCu3O7 became a 60 K superconductor by partial substitution of Y with Ca.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering