The relations of specific heat anomaly with variation of oxygen content in BiSrCaCuO(2212)

We have investigated the phase transition of Bi_1.8Pb_0.2Sr₂CaCu₂O₈ samples with specific heat in low temperature. The phase transition temperatures depend on the oxygen contents. There is a relation between the specific heat anomaly and the oxygen contents in these samples. The specific heat anomaly peak is the largest for the optimum doped sample, the anomaly peaks are decreased for the underdoped samples. There are the phase segregation phenomenon when the oxygen is removed content in these Bi2212 system samples, their transition temperatures are about 60K and 90K. The peak of specific heat anomaly for the overdoped sample (Tc=60K) does not appeared. The resistance measurement shows that the phase transition temperature of these samples are the same as that of the specific heat measurement. The electronic specific heats C_e and the Debye temperature θ_D are calculated.