“…The precursor, which was made of BaCO 3 , CaCO 3 , and CuO in the ratio 2 : 2 : 3, was sintered at 900 C for 12 h in flowing high-purity oxygen gas. Since the stoichiometric mixture ratio, namely, HgO : Ba 2 Ca 2 Cu 3 -O y ¼ 1 : 1, tends to result in the formation of CaHgO 2 as a secondary phase, 7) we adopted the slightly Hg-deficient starting composition of Hg 0:75 Ba 2 Ca 2 Cu 3 O y (HgO : Ba 2 Ca 2 -Cu 3 O y ¼ 0:75 : 1). The mixture was pressed into a cylindrical shape, charged in a gold capsule, and then heated at 830 C under 2 GPa for 0.5 h, using a cubic-anvil HP apparatus (TRY Engineering, 180-ton press).…”