Structural features and superconductivity of Al-doped Y(RE)-123-type single crystals

Abstract

The structure of a series of highly Al-doped superconducting Y(RE)-123 (RE = rare earth element) single crystals was investigated by XRD and NMR methods. On the basis of the data obtained by the structural investigations combined with the studies of magnetic and optical properties, the formation of various superstructures in the samples of pseudo-tetragonal symmetry has been discussed. The correlation between the carrier concentration and T c-values has been determined. The superconductivity (at 70 K) was indicated even at the 2/3 and 1/3 Al substitution for Cu in the basal and CuO 2 planes, respectively, in the phase presumably of a perovskite-like structural type.

Distinct effects of Al3+ substitution at Cu-site and Al2O3 addition on step-like elastic anomalies and electron–phonon coupling constant in EuBa2Cu3O7−δ superconductors

“…According to the phase diagram of Y123 suggested by Ceder et al [41], a phase transition from ortho-I phase to the mixed ortho-I and ortho-III phase occurs around 200 K. This may be the reason for the sudden hardening as indicated by a step-like elastic anomaly around the same temperature during cooling. In the present work, because Al 3+ partial substitution in EuBa 2 (Cu 1−x Al x ) 3 O 7−ı (x = 0.06, 0.10) substitutes directly into Cu-O chains instead of CuO 2 planes [36,20], the substitution disturbs oxygen ordering in the chains and subsequently caused disappearance of the anomaly.…”

“…Elemental substitutions in place of Cu i.e. REBa 2 (Cu 1−x M x ) 3 O 7−ı have been reported to show slightly different effects; substitution of M = Al 3+ and Ga 3+ was suggested to go into Cu-O chains while substitution of M = Zn 2+ and Ni 2+ was suggested to occupy CuO 2 planes of RE123 compounds [19][20][21][22][23][24][25]. The former does not affect T c drastically for low dopant concentrations compared to the latter.…”