Influences of BaO doping on the properties of singe domain GdBCO bulk superconductors

Abstract

In this work, a series of single domain GdBCO bulk superconductors with different ratios of BaO addition in the solid phase pellet, is successfully fabricated to inhibit the Gd/Ba substitution in the growth process by the modified top seeded infiltration growth (M-TSIG) technique. The reaction of the precursor powders, the growth morphology, the magnetic levitation force (F), the trapped magnetic flux (Btr) and critical temperature (Tc) of the single domain GdBCO bulk superconductors are investigated in detail. First, the differential thermal analysis is performed on the precursor powders of 10 mg solid phase pellet (containing various amounts of BaO) and 15 mg liquid phase pellet in order to investigate the melting temperature (Tm) and the peritectic temperature (Tp) of the GdBCO superconductor system. The results show that the melting point of the precursor powder decreases by nearly 8℃ as the BaO composition increases from 0 wt% to 4 wt%, which leads to Tp decreasing with BaO content increasing. Second, the top view morphologies of the GdBCO samples are also discussed. All of the samples exhibit clear, fourfold growth sector boundaries on their top surfaces, and spontaneous satellite grains are observed in none of these samples. It can be seen that the different ratio of BaO addition cannot affect the growth morphology of the single domain GdBCO bulk superconductor. And thirdly, the levitation force and trapped field of each of the samples are measured under a zero field cooling state at 77 K by the three-dimensional magnetic force and field device. The values of the levitation force for the samples are slightly different for different ratios of BaO additions. The largest levitation force is 35 N, which is obtained in the sample with 2.5 wt%, and the smallest one is 28 N in the sample with 1 wt% BaO addition. And also, the trapped field of the sample can be attributed simply to the variation in the pinning strength. It can be obviously seen that these values fluctuate between 0.28 T and 0.32 T for these samples. Finally, the critical temperatures of the samples are measured by the vibrating sample magnetometer with an external magnetic field of 0.01 T. The samples exhibit outstanding features of high Tc, which indicates that these samples are of good quality and the Gd/Ba substitution is inhibited by the BaO addition. The above results show that the values of melting temperature (Tm) and peritectic temperature (Tp) of the samples have the decrease tendencies, and the superconducting properties of the samples (such as F, Btr and Tc) can be improved to a certain extent when the amount of BaO added ranges from 2 wt% to 4 wt%, which are very helpful in inhibiting the Gd/Ba substitution and fabricating the high-quality single domain GdBCO bulk superconductors.