A Comparative Study of Ge-Based Organometallic Additions to MgB2.

Four Ge-based organometallic (OM = C6 H10 Ge2O7 ) polymers with similar chemical composition were used as additions for MgB2. MgB2 (OM)0.0014 dense samples with a relative density higher than 97% were obtained by ex situ spark plasma sintering. The critical current density and the irreversibility magnetic field of the added samples are slightly improved at highmagnetic fields by repagermanium (Alfa Aesar) addition when compared to the pristine reference sample. Addition ofGe-straightchain polymer shows some improvement of the maximum volume pinning force, Fp max . There is no significant Ge substitution in the crystal lattice of MgB2, while C substitutes for B. Pinning mechanism is mainly of a point pinning type, with the grain boundary pinning mechanism strengthening at lower temperatures and when additives are not used. A relatively high amount of carbon in the samples washes out the Ge effects on pinning-force-related parameters. The structure and morphology of the polymer additive play an important role in dispersion whenmixing, impacting the quality of the superconducting properties. The nanosize dimension of the pristine MgB2 powder shows also some drawbacks in mixing and sintering. [ABSTRACT FROM AUTHOR]