Effect of sodium doping on the oxygen distribution of Hg-1223 superconductors

Low-temperature oxygen annealing was performed on Na-doped and undoped Hg-1223 phases. It is argued that Na could perturb the electronic band structure of the material by changing the distribution of oxygen in the Hg-O layer, which then could affect the superconductivity of the material during the annealing process. It has been found that T-c can be increased by more than 20 K using an annealing temperature of 300 degrees C for 10 h, while annealing above 350 degrees C leads to loss of superconductivity due to Hg loss. Normal state-p tends to decrease with increasing annealing temperatures up to 400 degrees C. In addition, flattening in the normal state-p curves of doped samples indicated an increasingly insulating behavior. (C) 1999 Elsevier Science B.V. All rights reserved.