A new 92 K high-T_c superconductor. Hg-containing Tl-based 1212 phase

Bulk superconductivity up to 92 K has been achieved in the mercury-containing curprate (Tl_0.5Hg_0.5)Sr₂(Ca_1-xY_x)Cu₂ O_7-δ when x=0.3. Based on X-ray and electron diffraction and electron probe microanalyzer results, we identify the phase responsible for the superconductivity to be similar to that of (Tl_0.5Pb_0.5)Sr₂CaCu₂O₇ (so-called 1212 phase) with a space group of P4/mmm and lattice constants of a ∼ 3.8 Å and c ∼ 12.0 Å. Moreover, neither superlattice nor intergrowth along the a^* and c ^* directions were observed by electron diffraction. An increase in Ca²⁺ doping, 0.5≤x≤0.3, into the Y³⁺ sites results in a maximum superconducting transition temperature (T_c) at around 92 K for x=0.3. For compositions x<0.3, a decrease in T_c was observed.