Property and Structure of YBa₂Cu₃O_7-x-Nb₂O₅ Composite

Abstract

Nb2O5-doped YBa2Cu3O7-x superconductors were prepared by heating at 950°C for 24 h in air and cooling to room temperature at a rate of 5°C/min in air. The bulk density and critical current density (J c, 77 K and H=0 T) increased with increasing amount of Nb2O5≦0.5 wt%; up to 5.80 g/cm3 and 437 A/cm2 (sample thickness 1 mm), respectively. The critical temperature (T c (zero)) was about 92 K. Experimentally we have succeeded in improving the superconducting properties, microstructure and degradation in moisture with addition of Nb2O5≦0.5 wt%.

Effect of Nb doping on properties of Y-Ba-Cu ceramics

“…Though in more recent investigations [5-71 the maximum value J, = 570 A an-' [4] has not been exceeded, the study of the effect of Nb on the electrophysical properties of YBa,Cu,O, is worth investigating for the following reasons. First, upon the addition of Nb (no more than 0.5 wt%), the value either was constant (T, = 92 K [5, 6,8,91) or was greater ( T y = 92.5 K [7] and 095%2048/93/080589 + 04 507.50 0 1993 IOP Publishing Ltd 92.8 K [lo]) than in undoped ceramics prepared by the same method. Second, the process of saturation of the ceramics by oxygen accelerates in the presence of Nb, promoting a substantial decrease in the sample cooling time after high-temperature annealing [6, 81.…”

Oxygen stabilization in YBa2Cu3O6+δ:Ta2O5sintered in air

“…On the other hand, if Ta 5+ ions had been substituted for Cu (Cu 2+ , Cu 3+ ) or Y 3+ , the lattice parameters would have shown a more pronounced dependence on x [14]. In this latter case T c (onset) also should have shown a strong x-dependence [10][11][12][13][14]. However, we see a weak x versus T c (onset) relation in figure 1 which is consistent with the known δ versus T c (onset) [14] when δ > 0.8 (figure 3).…”

“…The need for oxygen diffusion has also limited the technological applications of this material. In some reports the group Va elements have been added to incorporate and stabilize the stoichiometric excess of oxygen in this system [9][10][11]. Paulose et al observed that the 123 doped with Nb 2 O 5 did not require the oxygen annealing step to obtain the superconducting transition at 91 K [9], which was attributed to the excess oxygen absorption by the samples in the presence of phases associated with Nb such as YBa 2 NbO 6 .…”

Structural and Electrical Properties of Niobium Doped Y<sub>0.6</sub>Gd<sub>0.4</sub>Ba<sub>2-x</sub>Nb<sub>x</sub>Cu<sub>3</sub>O<sub>7-y</sub> Superconductors

“…One of the most fascinating challenges of the material science is to develop YBa 2 Cu 3 O 7-x (YBCO) and RE-Ba 2 Cu 3 O 7-x (REBCO: RE = Er, Nd, Gd, Sm) superconductors for practical applications [6]. Several attempts have been made to study the effects of substituting Nb for YBCO [7][8][9][10][11][12][13]. In a study by Suresha et al [14], a resistivity for YBa 2 Cu 3-x Nb x O 7-y sample with x = 0.3, 0.45 and 0.6 indicated that T c was in the range 85 -90.3 K. They showed a possible change in crystal structure and composition with changing of x. Kuwabara and Kusaka [13] concluded that Cu and Nb did not co-exist in the same compound containing Y and Ba.…”