Synthesis, Structure and Superconductivity of (Hg_<0.65>V_<0.35>)Sr_2(Ca_<1-x>Nd_x)Cu_2O_z

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Using the sealed silica-tube method, we have successfully synthesized Hg-1212 superconductors (Hg_<0.65>V_<0.35>)-Sr_2(Ca_<1-x>Nd_x)Cu_2O_z in the range of 0.35 &≤ x &≤ 0.55. Rietveld refinement on the X-ray diffraction data is carried out on the basis of tetragonal space group P4/mmm. Refined occupation factors of V in the Hg site and Nd in the Ca site as well as of oxygen at (1/2, 1/2, 0) on the (Hg, V)O_δ layer give a chemical composition (Hg_<0.61>V_<0.39>)Sr_2(Ca_<0.41>Nd_<0.59>)Cu_2O_<6.78> for the as-prepared sample with the nominal composition of (Hg_<0.65>V_<0.35>)Sr_2(Ca_<0.55>Nd_<0.45>)Cu_2O_z. The variation of T_c with x and T_c enhancement after O_2 annealing indicate that the compounds are in the underdoped region. The highest onset T_c of 105 K is attained in the O_2-annealed sample with x=0.35.
社団法人応用物理学会の論文
1997-10-15