SPECIFIC-HEAT OF THE HIGH-TC SUPERCONDUCTOR (BI,PB)2SR2CA2CU3O10, AND RELATED PHASES CA2CUO3 AND (CA0.86SR0.14)CUO2 FROM 0.4 TO 20 K

Specific heat, Cp, data from 0.4 to 20 K for four polycrystalline specimens of (Bi, Pb)2Sr2Ca2Cu3O10 are reported, and compared with similar measurements made on Bi2Sr2CaCu2O8. Both the upturn in Cp/T and the coefficient of the linear term, γ0, are sensitive to the phase composition of the specimen. γ0 decreases from 10.8 mJ/(mol K2) in the specimen that has roughly equal proportions of the low-Tc (2:2:1:2) and high-Tc (2:2:2:3) phases to zero in the specimen that is close to 100% 2:2:2:3 phase. The variability of γ0 with phase purity suggests that it is extrinsic to the superconducting state of (Bi, Pb)2Sr2Ca2Cu3O10. Above 4 K, Cp of (Bi, Pb)2Sr2Ca2Cu3O10 shows a rapid departure from simple T3 (Debye) behavior due to dispersion and the excitation of low-lying optic modes. Values obtained for the Debye temperature, θD0, are in the range 276-292 K for (Bi, Pb)2Sr2Ca2 Cu3O10 (cf. 253 ± 7 K for Bi2Sr2CaCu2O8). To better understand how other copper-oxide compounds, which may appear as impurity phases in this system, contribute to Cp of (Bi, Pb)2Sr2Ca2Cu3O10 we have carried out Cp measurements between 0.4 and 20 K on Ca2CuO3 and on the structural parent phase (Ca0.86Sr0.14)CuO2. For Ca2CuO3, no upturn in Cp/T is observed and values of 1.63 mJ/(mol K2) and 516 K are obtained for γ0 and θD0, respectively. (Ca0.86Sr0.14)CuO2 behaves somewhat differently with an upturn in Cp/T, γ0=0 mJ/(mol K2) and θD0=496 K. © 1990.