Relationship Between Electronic and Crystal Structure in Nd 1 + x Ba 2 − x Cu 3 O 6 + δ

Abstract

In accordance with a relation between the lattice parameter c and the concentration of holes p, which has been found earlier for the YBa 2 Cu 3 O 6+ compound, we obtain the p parameter in the same manner for the solid solution Nd 1.2 Ba 1.8 Cu 3 O 6+ with substitution of Nd 3+ for Ba 2+ in barium sites. For this, structural and superconducting properties of the Nd 1.2 Ba 1.8 Cu 3 O 6+ samples stored for specified times  after quenching from annealing temperatures have been studied. The investigation shows that Nd 1.2 Ba 1.8 Cu 3 O 6+ stored for a long time has quite a low critical temperature T c extending only to T c onset = 55 K for the most oxidized sample with  = 0.953. We find that the -dependence of the lattice parameter c significantly changes with time . When using the relation between c and p, the existence of electron doping of 0.045 per Cu in Nd 1.2 Ba 1.8 Cu 3 O 6+ can be inferred. This doping explains well reduced T c in Nd 1.2 Ba 1.8 Cu 3 O 6+ . In addition, we observe a local drop of T c by up to 20 K for the samples with p ~ 0.095 ( ~ 0.8) similar to decreasing T c known as "anomaly 1/8".

Evolution of the Crystal and Electronic Structures of the RBa2Cu3O6 + δ Cuprates in Annealing

“…We also have found that heterovalent substitution at the cation sites next to a structural CuO 2 plane results in the following effect, which is similar to the well-known 1/8 anomaly [7][8][9]: a sharp drop in T c in the narrow δ range that corresponds to a hole concentration of 1/8 in a CuO 2 plane. In this work, we use some results from our earlier works [10,11].…”