A nearly single phase (Hg,Tl)-bilayer sample, (Hg0.7,Tl0.3)2Ba2(Ca0.2,Y0.8)Cu2Oy, was synthesized by a high pressure synthesizing technique. The as-sintered sample, which is considered to be underdoped, shows superconductivity at Tc = 65 K. The sample was then annealed in Ar gas at 300 °C for 30 min, 12 h, and 400 °C for 36 h, respectively. The crystal structure of these samples was determined by Rietveld refinement. Both of the a- and c-axes lengths expand with the decrease of hole doping in the crystal. It was found that the interplanar distance between the Ba-(rock salt)-Ba sheets expands, and the interplanar distance between the Ba-(infinite layer)-Ba sheets shrinks with Ar annealing, showing the same variation tendency as found in (Hg,Tl)-2223.
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