THERMAL STABILIZATION OF IMPURITY HGCAO2 AND SUPERCONDUCTING PHASE HG(SN)BA2CA2CU3O8+DELTA IN HG0.9SN0.1BA2CA2CU3O8+DELTA SUPERCONDUCTOR

Tin-doped samples Hg0.9Sn0.1Ba2Ca2Cu3O8+delta ((Hg0.9Sn0.1)-1223) were synthesized in sealed silica tubes by a solid-state reaction method. The dominant phase involved in the sample is a superconducting phase o f Hg(Sn)Ba2Ca2Cu3O8+delta (Hg(Sn)-1223), which is a solid solution of Sn in the compound HgBa2Ca2Cu3O8+delta. An impurity phase HgCaO2 also exists together with the dominant phase. The results of thermogravity analysis and XRD analysis show that the impurity phase HgCaO, and supe rconducting phase Hg(Sn)-1223 have different decomposition temperature s in flowing He gas and in flowing O-2 gas atmosphere. The onset decom position temperatures of these two phases measured in flowing He gas a re 560 and 760 degrees C respectively. They increase to 576 and 825 de grees C respectively in flowing O-2 gas. Studies of the effect of anne aling temperature on T-c by resistance measurement for this sample sho w that the superconductivity is reversible in Rowing O-2 gas below the decomposition temperature of the superconducting phase Hg(Sn)-1223, n amely 825 degrees C. The quality of the superconductor, including the critical temperature and the sharpness of the transition, can be impro ved by removing the impurity phase HgCaO2 from the sample using a high -temperature annealing process under Rowing O-2 gas.