The structures of the 126 Ba 2Ca 2Cu 3(Ca xCu y)O 8+δ the 116 K Ba 2Ca 3Cu 4(Ca xCu y)O 10+δ and their transformed products

Abstract

Two new superconducting Ba Ca Cu oxides were identified as Ba 2Ca 2Cu 3(Ca xCu y)O 8+δ and Ba 2Ca 3Cu 4(Ca xCu y)O 10+δ with T c of 126 K and 116 K, respectively. The cations (Ca xCu y), 0.4≤x≤0.9and0≤v≤0.7, are inserted between two adjacent BaO layers to stabilize the structures and to adjust the Cu-valences. Both compounds show the body-centered symmetry, but with different lattice constants of ( a,c) = (3.8, 28.2) and (3.8, 34.8) Å, respectively. These compounds are unstable against the incorporation of CO 2 and H 2O in open air. The transformed products (Ca u/2Cu v/2C xH y) 2Ba 2Ca 2Cu 3O 8+δ and (Ca u/2Cu v/2C xH y) 2Ba 2Ca 3Cu 4O 10+δ have an expanded c of 33.8 and 40.2Å, and a lower T c of 90 and 114 K, respectively. The structure models for these decay products are proposed.