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The degradation of the superconducting phase Bi1.65Pb0.35Sr1.8Ca2.2Cu3Oy and its characteristics: electrical resistivity R, critical temperature Tc (R=0), critical current density jc, and volume fraction of Meissner phase Cm, have been investigated at 550–810°C and PO2=2·101…1·105 Pa by X-ray diffraction, resistance, inductance and magnetic methods. It was established that at PO2≥103 Pa degradation of the ceramic samples runs through the solid solutions decomposition. As a result, the intergrain critical current is decreased 10–20 times while the intragrain one is increased 1.5–2 times. At PO2=101−102 Pa the inter- and intragrain critical currents are decreased by 5–10 times and by 1.5–2 times respectively as a result of oxygen extraction without visible destruction of the Bi,Pb-2223 structure.