Observation of superconductivity in (Y 1− xCa x)Ba 2Cu 3O 6

Abstract

Substitution of Ca 2+ for Y 3+ in YBa 2Cu 3O 6 converts this tetragonal semiconductor into a tetragonal superconductor with a T c of 50 K. Furthermore, the structure of (Y 0.8Ca 0.2)Ba 2Cu 3O 6, determined by neutron powder diffraction, is fully consistent with partial oxidation of the Cu(2) O sheets, whereas the linear O Cu(1) O units do not undergo oxidation. Observation of a limited solid solubility for Ca 2+ in this structure is attributed to a maximum allowed oxidation state for Cu(2). This implies that in the superconductor YBa 2Cu 3O 7 the Cu O chains are responsible for the T c of 90 K, whereas the Cu O sheets alone produce superconductivity at 50 K in YBa 2Cu 3O 6.5.