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 YBa2Cu3O6+d compound, we obtain the p parameter in the same manner for the solid solution Nd1.2Ba1.8Cu3O6+d with substitution of Nd3+ for Ba2+ in barium sites. For this, structural and superconducting properties of the Nd1.2Ba1.8Cu3O6+d samples stored for specified times t after quenching from annealing temperatures have been studied. The investigation shows that Nd1.2Ba1.8Cu3O6+d stored for a long time has quite a low critical temperature Tc extending only to Tconset = 55 K for the most oxidized sample with d = 0.953. We find that the d-dependence of the lattice parameter c significantly changes with time t. When using the relation between c and p, the existence of electron doping of 0.045 per Cu in Nd1.2Ba1.8Cu3O6+d can be inferred. This doping explains well reduced Tc in Nd1.2Ba1.8Cu3O6+d. In addition, we observe a local drop of Tc by up to 20 K for the samples with p ~ 0.095 (d ~ 0.8) similar to decreasing Tc known as "anomaly 1/8".