B4C in ex-situ spark plasma sintered MgB2

• B4C-added MgB2 was prepared by ex-situ spark plasma sintering.
• Processes are fast and effective for C-substitution even if the B4C raw powder particles are large (4 μm).
• Jc at high H is higher than for pristine or nano-SiC-doped samples.
• Jc (20K, 5.35T) = 100 A/cm2 for the optimum sample MgB2(B4C)0.01.
• Pinning is in the PP limit and GBP depends on the B4C-addition amount.

Powder mixtures of MgB2 and B4C with composition ((MgB2) + (B4C)x, x = 0.005, 0.01, 0.03) were consolidated by Spark Plasma Sintering at 1150 °C for 3 min. The average particle size of B4C raw powder was relatively high of 4 μm. Despite this, it is shown that processing processes are fast and, as in the case of the in-situ routes, for our ex-situ method carbon substitutes for the boron in the crystal lattice of MgB2. Specifics of microstructure are discussed based on electron microscopy observations. Carbon substitution and microstructure contribute to enhancement of the critical current density Jc at high magnetic fields and of the irreversibility field Hirr. Samples are shown to be in the point pinning limit with some tendency toward the grain boundary pinning depending on B4C doping amount and temperature. An optimum composition is found for x = 0.01: for this sample, at 20 K, a Jc of 100 A/cm2 is obtained at 5.35 T. This value is higher than for the pristine MgB2 sample and for an optimum ex-situ nano-SiC-doped sample obtained for the same SPS processing conditions.