ANNEALING CONDITION, T-C, AND OXIDATION ENTHALPY IN HGBA2CUO4+DELTA

To obtain a broad range of T-c for HgBa2CuO4+delta (Hg1201) by anneali ng, the oxidation thermodynamics and oxygen diffusion have been studie d. During annealing, delta is controlled by the oxygen partial pressur e P(O-2) as well as the annealing temperature T-a with the oxidation e nthalpy Delta H and the oxidation entropy Delta S as key parameters. O ur data suggest that the Delta H of Hg1201 significantly depends on de lta, which makes the partial derivative delta/partial derivative P(O-2 ) of Hg1201 smaller than that of YBa2Cu3O7-delta in a practical T-a ra nge. Therefore, a wider P(O-2) range are necessary. By choosing proper annealing parameters, Hg1201 samples with O K less than or equal to T -c less than or equal to 97 K on the underdoped side and 97 K greater than or equal to T-c greater than or equal to 20 K on the overdoped si de were obtained.