Development of c-Axis Oriented MgB₂ Bulks by Magnetic Field Orientation Method

Abstract

  Synthesis of c-axis oriented MgB₂ bulks was attempted by magnetic orientation technique combined with the electrophoretic deposition (EPD) and the hot pressing (HP) method. Using home-made or commercialized MgB₂ powder, EPD was performed under 10 T at room temperature. The EPD-processed films were inserted in SUS316 sheath, uniaxially pressed into a tape shape and sintered at 900°C for 24 h in evacuated quartz ampoules. In addition, HP samples were made by heating at 900°C for 6 h in Ar flow under 30 and 100 MPa. X-ray diffraction analysis revealed that the EPD-processed film in 10 T showed ~15 times higher intensity ratio, I₀₀₂/I₁₀₁, than those of randomly grain-oriented ex-situ bulks. This suggests EPD under field is a promising way to synthesize c-axis oriented MgB₂ tapes. The c-axis oriented tapes showed much higher critical current density J_c than randomly oriented bulks and excellent high J_c of 6.9×10⁵ A/cm² was recorded at 20 K. Our study shows a combination of c-axis orientation and an increase in bulk density is a quite effective way to synthesize ex-situ MgB₂ tapes and bulks with dramatically enhanced critical current properties.