High magnetic field enhancement of the critical current density by Ge, GeO2 and Ge2C6H10O7 additions to MgB2

Ge, GeO2 and Ge2C6H10O7 additions to MgB2 obtained by ex situ spark plasma sintering significantly enhance the critical current density Jc in high magnetic fields. A Jc(T = 20 K) of 102 A cm−2 is obtained at 3.9 T in the pristine sample and at 5.8 T in the MgB2(Ge2C6H10O7)0.0014 sample. The decrease in the critical temperature for added samples is less than 1 K and Jc(20 K, H = 0) shows a small decrease from 5.5 × 105 A cm−2 in the pristine sample to 3.9 × 105 A cm−2 in MgB2(Ge2C6H10O7)0.0014 sample. Ge does not substitute into the MgB2 lattice.