Tomonori Tamura

High pressure syntheses of copper oxychlorides with K2NiF4-type and related structures

Several new copper oxychlorides with the K2NiF4-type and related structures (the 02(n-1)n where n=1, 2 and 3, and the 0222 structures) are synthesized using a high pressure technique. These are (Ca,K)2CuO2Cl2 (Tc = 24 K), Ba2CuO2Cl2 for the 0201; (Sr,Ca)3Cu2O4+δCl2−y (Tc = 80 K) for the 0212; (Sr,Ca)4Cu3O6+δCl2−y (Tc = 46 K) for the 0223; CaLnCuO3Cl (Ln=Y, Ho, Er) for the 0222. Hole carrier doping to induce superconductivity and size tuning of the CuO2 sheet are attained in these new oxychlorides.

High-pressure synthesis of a new homologous series of superconductors, (Hg1−xTIx)2Ba2Can−1CunOy (0.3 ≤ x ≤ 0.6,n=3,4)

We have recently synthesized new superconducting cuprates containing a mercury-based bilayer, i.e. (Hg,Tl)2Ba2(Ca,Y)Cu2Oy and (Hg1−x Tlx)2Ba2 Can−1 CunOy (x ∼ 0.4, n = 3,4) by a high-pressure technique. These compounds are the n=2, 3 and 4 members of a new homologous series, (Hg, Tl)-22(n−1)n. The effects of Tl substitution for Hg on the formation and superconductivity of the (Hg, Tl)-2223 and -2234 phases are investigated. Both the phases are stabilized for the Tl content x of 0.3–0.6. Tc of the as-synthesized (Hg,Tl)-2223 compound increases from 45 K to 81 K with an increase in x. In contrast, Tc of the (Hg,Tl)-2234 compound is almost independent of x (∼114 K).