Abstract Body

The RE-123 system of REBa₂Cu₃O_y(RE = rare-earth elements) with the superconducting transition temperature (T_c) of around 90 K is a promising candidate as a practical superconducting magnet. The enhancement of T_c is desired for the operation at liquid nitrogen temperatures. The oxygen content y in REBa₂Cu₃O_yis around 6.9, indicating that ~10% of the oxygen ions (O^2-) in the Cu-O chain is deficient. Since the disorder in the oxygen-deficient Cu-O chain will suppress the superconductivity in the adjacent CuO₂ plane, the reduction of the oxygen deficiencies is crucial for the enhancement of T_c. Additional O^2- can be incorporated into the oxygen deficient Cu-O chain through the RE³⁺-substitution for Ba²⁺ to maintain the charge neutrality. However, it has been reported that T_c decreases with increasing xfor x ≥ 0.1 in Nd_1+xBa_2-xCu₃O_y, which has the highest T_c in RE-123 system [1]. In this work, we report the enhancement of T_c in the narrow range of x ≤ 0.05 for Nd_1+xBa_2-xCu₃O_y.

Polycrystalline samples of Nd_1+xBa_2-xCu₃O_y with x ≤ 0.05 were prepared by sintering in flowing Ar gas followed by annealing in flowing O₂ gas. It has been found that the oxygen content y increases with increasing x without any change in the hole concentration in the CuO₂ plane p as shown in Fig. 1. Furthermore, T_c also increased to 96.4 K for x = 0.05 from 94.8 K for x = 0. The slight enhancement of T_c through the Nd-substitution for Ba may be attributed to the reduction of the disorder in the oxygen-deficient in the Cu-O chain.

References

[1] N. Chikumoto et al., Appl. Supercond. 2, 163 (1998).

Acknowledgment

This work was supported by JST SPRING, Grant Number JPMJSP2114.

Figure 1. x dependence of T_c, oxygen content y and hole concentration in the CuO₂ plane p in Nd_1+xBa_2-xCu₃O_y with x ≤ 0.05.

Keywords: RE-123, substitution, oxygen deficiency, T_c