CADMIUM SUBSTITUTION IN YBA2CU3O7-DELTA AND BI2SR2CACU2O8+DELTA

The chemical interactions of CdO with YBa2Cu3O7-delta, Bi2Sr2CaCu2O8+delta, and related oxides are examined. Mixtures of CdO with other oxides (Y-Ba-Cu-O, BaO2, CuO, Y2O3, Bi-Sr-Ca-Cu-O, CeO2, and CaO) were heated to 800-900-degrees-C under N2, O2, air, and 1.5 GPa quasi-hydrostatic pressure. The reacted samples were characterized by powder X-ray diffractometry, thermogravimetric analysis, and dc resistivity and ac magnetic susceptibility measurements. CdO was found to be chemically inert under most of these conditions. When CaO is present, the cubic CaCdO2 is formed. Cadmium(II) can be partially substituted for yttrium(III) (up to 30 mol %) in YBa2Cu3O7-delta without detriment to superconducting properties. Although Cd2+ is aliovalent to Y3+, charge compensation is achieved by the formation of additional oxygen vacancies, as evidenced by TGA measurements. This oxygen vacancy formation occurs rather than the expected change in hole concentration in the CuO chains and planes. Also, investigations of CdO substitution by other groups are reviewed.