Dependence of physical properties on Bi/Sr ration and oxygen content of Bi_2+xSr_2-xCaCu₂O_8+δ

In order to extract the fundamental physical properties of high transition temperature (high-T_c) superconductors, one needs to take account of the details of real materials which possibly affect their properties. In the case of Bi₂Sr₂CaCu₂O_8+δ (Bi2212), non-stoichiometry due to the intersubstitution between Bi and Sr atoms exists, yielding its composition Bi_2+xSr_2-xCaCu₂O_8+δ. Accordingly, the number of hole carries (n_h) as well the magnitude of chemical inhomogeneity depends on x and δ (oxygen content). In order to evaluate the precise x- and δ- dependence of the physical properties, high-quality single crystals of Bi2212 with x=0.10, 0.15, and 0.20 were grown by the Travelling-Solvent Floating Zone (TSFZ) method. The δ values were systematically changed by annealing the as-grown crystals under various conditions. To evaluate n_h, we performed XAFS measurements, in which the pre-peak intensity of the oxygen K-edge absorption spectra is known to a measure of n_h. We have successfully established the relationship between n_h and T_c of the Bi2212 system with different amount of chemical inhomogeneity (x’s). The details of these characteristics will be presented in the meeting.