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

Danlu Zhang,Michael D Sumption,Mike Tomsic,Matt Rindfleisch,Fang Wan,Edward W Collings,C J Thong

doi:10.1088/1757-899x/756/1/012019

Abstract

MgB2 superconducting wires and bulks with nano-La2O3 addition have been studied. A series of MgB2 superconducting bulk samples with nano-La2O3 addition levels of 0, 5, 7, 18wt% were prepared. AC resistivity data showed slight increases of Bc2 and unchanged Birr for the bulk samples with doping levels lower than 7 wt% and decreased critical fields for the heavily doped (18 wt%) bulk. X-ray diffraction (XRD) showed the presence of LaB6 in the nano-La2O3 doped MgB2 bulk samples and decreased MgB2 grain size in nano-La2O3 doped bulks. Monocore powder-in-tube (PIT) MgB2 wires without and with 5 wt% nano-La2O3 addition (P-05) were prepared for transport property measurement. 2mol%C-doped Specialty Materials Inc. (SMI) boron powder was used for wire P-05 and previously prepared control wires (control wires were made without the addition of nano-La2O3 powder, W-00 and P2). Low field magnetic properties were obtained from magnetization loop (M–H), transport critical current density (Jc) was measured at 4.2 K for the nano-La2O3 doped PIT wire (P-05) and the control samples (P2 and W-00). The transport critical current density Jc (B) of P-05 at 4.2 K and 8 T (6.0 ×104 A/cm2) was twice that of the control wire. The critical magnetic fields (Bc2 and Birr ) of P-05 and the control sample P2 were compared. The critical fields of P-05 were slightly less than those of P2. Kramer-Dew-Hughes plots indicated a change from surface pinning to a mixture of volume pinning and surface pinning. It is shown that enhancement of P-05’s transport properties is due to additional flux pinning by the fine-size rare-earth borides rather than enhanced Bc2 or Birr.

Highlights

Since the discovery of MgB2 superconductors in 2001 [1], substantial improvement on the material has been achieved in terms of critical field, transport property, wire manufacture processes
The best “non barrier” transport Jc values were obtained by the advanced internal magnesium infiltration (AIMI) approach, with the addition of C and Dy2O3 (1.07 × 105 A/cm2) at 10 T, 4.2 K, [13]
Many chemicals have been added to MgB2 in the past 18 years to study their effects on the resultant transport and other superconducting properties, such as upper critical field (Bc2) [14,15], and irreversibility field (Birr) [16,17]

Summary

Introduction

Since the discovery of MgB2 superconductors in 2001 [1], substantial improvement on the material has been achieved in terms of critical field, transport property, wire manufacture processes. Many chemicals have been added to MgB2 in the past 18 years to study their effects on the resultant transport and other superconducting properties, such as upper critical field (Bc2) [14,15], and irreversibility field (Birr) [16,17]. In addition to C and C containing materials, doping with Dy2O3 has shown to increase both Jc and Birr [19,20]. La2O3 was chosen because some rare-earth oxide additions have improved Jc and Bc2/Birr [19,20,21,22,23,24] in MgB2 superconductors. Transport Jc in the 5 wt% nano-La2O3 doped monocore PIT-processed MgB2 wire increased to twice the value of the control sample at 4.2 K, 8 T

Sample preparation

Measurements

Bulk sample’s magnetic and structure properties

Wire sample

Flux pinning in response to La2O3 doping

Concluding Discussion