CROSS-SUBSTITUTION OF BI AND SR IN BI2SR2CACU2O8+DELTA

The continuously varying solid solution in the Bi2+xSr2-xCaCu2O8+delta system has been clarified within the range -0.1 < x < 0.2. The c lattice parameter decreases with increasing x. In the Bi excess region, the oxygen content, as determined by titration and thermal gravimetry, increases with increasing x, while it remains constant in the negative region. A change in the critical temperature, T(c), is also examined, in view of oxygen content and carrier concentration of the samples. The behavior of T(c) versus x in the Sr excess region for the quenched samples differed from that for the slowly-cooled samples, which is explained by the difference in defect types introduced by substitution. The carrier concentration is constant in the region of excess Bi compositions. No significant effect of cross-substitution of Bi and Sr on flux pinning is magnetically observed; aliovalent ions do not enhance flux pinning in this system.