OXYGEN STOICHIOMETRY, STRUCTURE AND SUPERCONDUCTIVITY IN BI2SR2CACU2O8+X

Bi2Sr2CaCu2O8+x (2212) was synthesized from freeze-dried precursors. The oxygen content of 2212 was determined as a function of temperature and oxygen partial pressure by thermogravimetry. Four-probe resistivity measurements performed on 2212 confirmed the results of thermogravimetry. The influence of oxygen nonstoichimetry on the structure and T-c of 2212 was determined. It was found that 2212 without excess oxygen (x = 0) is superconducting. This points to the role of the (Bi-O)(infinity) layers as a source for holes in 2212. It was also found that samples of 2212 with the same oxygen content had different T-c's depending on thermal history. This difference in T-c is thought to arise from oxygen occupying different sites in the lattice while maintaining the same total oxygen content. The conclusions are indirectly supported by measurements of the rates of oxygen intercalation and oxygen removal in 2212.