Two kinds of sintering atmosphere, N2and air, were used to study the effect of atmosphere on the formation of the lowTcphase and the highTcphase. The annealing temperatures were 810 °C in N2and 850 °C in air. The resistivity measurements and the x‐ray diffraction analysis showed that while the fraction of the highTcphase continued to increase with sintering times in air, it did not increase in any appreciable amount even after 264 h of sintering in N2atmosphere. Compared with air, N2atmosphere enhanced the formation of the lowTcphase and inhibited the formation of the highTcphase.