THE ROLE OF CuO CHAIN LENGTH ON SUPERCONDUCTIVITY EMERGENCE IN YBa2Cu3O6.30

Abstract

The authors investigate the tetragonal(T)-orthorhombic(O) transient zone of YBa 2 Cu 3 O 6+x , in a comparative way on pair samples one of which is produced by deintercalation [D] and the other by intercalation [I] of intrinsic oxygen in the basal Cu(1)O x plane and having the same oxygen content (k) and thermal history. Resistive and electron diffraction measurements, performed on [D] k - [I] k pairs within the composition range 0.28 ≤ k ≤ 0.32, are reported. Direct evidence is provided that the T-OII transient is a structural and electronic two phase region characterized by the (T+OII) [D] 0.30 non-superconducting (non-SC) and (OII+OIII*) [I] 0.30 superconducting (SC) phases. The OII superstructure represents the minority component of [D] 0.30 phase and the majority one of [I] 0.30 and OIII* is a new orthorhombic anti-OIII superstructure. The nature of the non-SC and SC behaviours has been comparatively investigated by NQR analysis at the T-OII borderline. The evaluated different values of the average chain lengths emphasize the role of the Cu-O chain length on the hole doping efficiency in YBCO at constant oxygen content.