PHASE-SEPARATION AND OXYGEN VARIATION IN PR-DOPED BI2SR2CACU2O8+DELTA

The structural and electrical properties of Bi2Sr2Ca1-xPrxCu2O8+delta have been investigated as a function of x. Powder-x-ray-diffraction pa tterns indicate that this system forms a continuous solid solution. It is found that phase separation exists in this system. Two phases with different modulated periods appear as the Pr doping changes. At low d oping levels, the short-period phase dominates, while at high doping l evels the long-period phase dominates. The short-period phase and the long-period phase are thought to correspond to the poor-Pr- and rich-P r-concentration phases, respectively. T(c) was found to increase sligh tly for x less-than-or-equal-to 0.1, decrease linearly for 0.1 less-th an-or-equal-to x less-than-or-equal-to 0.4, then to be depressed rapid ly for 0.4 less-than-or-equal-to x less-than-or-equal-to 0.5, and fina lly to disappear at x = 0.6. The valence of Pr was inferred to be clos e to +3 from the measurement of the oxygen content and the comparison with other rare-earth-doped Bi-2212 systems. The variation of T(c) was explained in terms of hole filling and phase separation.