Influence of Metal Diboride and Dy2O3 Additions on Microstructure and Properties of MgB2 Fabricated at High Temperatures and under Pressure

Abstract

High temperatures and under pressure (HTP) processing has been used to study the effects of chemical doping in MgB2. ZrB2, TiB2 and NbB2 were selected as additives since, like MgB2, they have an AlB2-type structure and similar lattice parameters. Dy2O3 was selected as it has been reported to generate nanoscale, secondary intragrain phases in MgB2. While C is known to enter the B-sublattice readily, attempts to dope Zr and other elements onto the Mg site have been less successful due to slow bulk diffusion, low solubility in MgB2, or both. We have used high-temperature, solid-state sintering (1500 °C), as well as excursions through the peritectic temperature (up to 1700 °C), to investigate both of these limitations. Bulk MgB2 samples doped with MB2 (M = Zr, Ti and Nb) and Dy2O3 additions were synthesized and then characterized. Lattice distortion and high densities of crystal defects were observed in the MgB2 grains around nano-sized MB2 inclusions, this highly defected band contributed to a large increase in Bc2 but was not large enough to increase the irreversibility field. In contrast, distributed intragrain precipitates were formed by Dy2O3 additions which did not change the lattice parameters, Tc, Tc distribution or Bc2 of MgB2, but modified the flux pinning.

Increased flux pinning force and critical current density in MgB2 by nano-La2O3 doping

“…Based on the data in Figure 1 , it can be seen that T c of the doped bulks did not change compared to the control bulk sample. This is similar to the unchanged T c observation on Dy 2 O 3 doped MgB 2 bulks [ 29 ], meaning no significant atomic substitution occurred on MgB 2 host lattice sites.…”

“…In contrast, the curve for P-05 wire peaked at around b = 0.168. This phenomenon has been observed in Dy 2 O 3 doped samples [ 29 ] and Yang et al [ 29 ] stated that two reasons can be responsible for this behaviour: (1) The doped sample might contain a set of local B k s instead of one distinct value, which can lead to an artificial error in the estimation of the peak positions; (2) The deviation from b peak = 0.2 might be due to other pinning mechanisms (e.g., normal volume pinning in which f p maximizes at b < 0.2 due to anisotropy [ 33 ]) in association with the GB pinning. The presence of LaB 6 peaks in all the XRD patterns of the doped bulk samples strongly suggests that LaB 6 , formed by reaction with the B powder, would also be present in the doped wires and as such would be responsible for the observed volume pinning.…”

High Trapped Fields in C-doped MgB2 Bulk Superconductors Fabricated by Infiltration and Growth Process

“…Recently, Yang et al . also observed such shift for MgB 2 containing Dy 2 O 3 54 . Dy based nano-inclusions were considered to form additional pinning sites and the origin of the observed shift.…”

Maximum reduction of energy losses in multicore MgB2 wires by metastructured soft-ferromagnetic coatings

“…Now, there are multiple pathways to be considered when optimizing SC multifilamentary wires. On the one hand, there are extrinsic techniques like chemical doping 66 – 68 or irradiation treatments 69 – 71 , which both can enhance the by improving the flux pinning mechanism, but do not change that the AC-losses will still be dominated by the contributions of the SC filaments and its metallic matrix. On the other hand, extrinsic methods such as the twisting of the filaments can lower the AC-losses, but at the expense of an undesired reduction of 58 .…”