High-Pressure Synthesis of Ba_2Ca_(n-1)Cu_nO_(2n)(O,F)_2 (n=2approx5) with the highest T_c of 120 K (n=3)

摘要

The homologous series of superconducting cuprate with apical fluorine, Ba_2Ca_(n-1)Cu_nO_(2n)(O,F)_2 (n=2approx5), was prepared under high-pressure. The nearly single-phase samples for n=3 and 4 were prepared from the nominal compositions of Ba_2Ca_2Cu_3O_(6.25+#delta#)F_(1.3) and Ba_2Ca_3Cu_4O_(8.4+#detal#)F_(1.0), respectively. The T_c is found to depend on the nominal F content and the highest T_c value of 120 K was observed for n=3. The carriers would be created by the substitution of O~(2-) for F~- rather than the interstitial fluorine and/or oxygen atoms. The highest T_c's for n=2, 4 and 5 obtained so far were about 90, 105 and 90 K, respecively. The c-axis length was expressed with c(A)=14.7+6.37(n-1).