Flux pinning and superconducting properties of melt-textured NEG-123 superconductor with TiO 2 addition

Abstract

We studied the effect of TiO 2 doping on flux pinning and superconducting properties of a melt-grown (Nd 0.33Eu 0.33Gd 0.33) Ba 2Cu 3O y + 35 mol% Gd 2BaCuO 5 (70 nm in size) composite (NEG-123) processed in Ar–1% O 2 atmosphere. As indicated by similar, sharp superconducting transitions, the small quantities of TiO 2 used in our experiments did not deteriorate superconducting properties of the NEG material. Transmission electron microscopy (TEM) analysis found 20–50 nm Ti-based particles in the NEG-123 matrix. However, we have not observed the clouds of <10 nm sized particles in the NEG-123 matrix, as in the case of recently reported NEG-123 composites doped by Mo and Nb nanoparticles. Nevertheless, quite a good J c – B performance in the 0.1 mol% Ti-doped sample, namely 550 kA/cm 2 at the self-field and at the secondary peak field (4.5 T) was achieved at 65 K, while 320 kA/cm 2 was obtained at zero-field at 77 K, and 50 kA/cm 2 at 90.2 K. The pinning effectiveness decreased with increasing Ti content above 0.2 mol%. The analysis of the pinning force showed that higher concentration of Ti (>0.2 mol%) increased the amount of normal pins ( δl pinning), indicated by the Fp( h) peak shift from h = 0.42–0.36. The maximum pinning effect in a broad field range could be achieved by optimizing Ti content and adding sub-micron Gd-211 particles.