New oxycarbonate superconductors (Cu0.5C0.5)Ba2Can−1CunO2n+3 (n=3, 4) prepared at high pressure

✍ Scribed by T. Kawashima; Y. Matsui; E. Takayama-Muromachi

• Publisher: Elsevier Science
• Year: 1994
• Tongue: English
• Weight: 550 KB
• Volume: 224
• Category: Article
• ISSN: 0921-4534
• DOI: 10.1016/0921-4534(94)90606-8

✦ Synopsis

In the process of searching for the phases of the Ag-Ba-Ca-Cu-O system at 1200 ° C under 5 GPa, we found the new oxycarbonate superconductors (Cuo.5Co.5) Ba2Can _ ~CunO2~ + 3. Two members of the series with n = 3 and n = 4 were isolated as almost single phases; their structures are closely related to those ofT1 (or Hg) based 1223 and 1234, respectively. The TI (Hg) sites are, in the present series, replaced by Cu and C. Disregarding ordering of Cu and C, the present compounds take tetragonal subcells; at= 3.859( 1 ), ct= 14.766(5 ) A for n= 3 and at= 3.855( 1 ), ct= 17.930(6) A for n=4. Electron microscopic observation indicated that Cu and C are, in both cases, located alternately along the a-axes of the subceUs resulting in superstructures having as=2at, bs=bt and cs=2ct. The n=3 member showed a superconducting transition at 67 K, while the n=4 member at 117 K which is the highest Tc among the oxycarbonate superconductors found thus far.