The effects of sintering temperature on superconductivity of MgB2 prepared by hot pressing

The MgB2 superconductor bulks were prepared by hot-pressing under the pressure of 55 MPa at different temperatures of 650 degrees C, 700 degrees C, 800 degrees C, 900 degrees C, 1000 degrees C, respectively, and the hot-pressing effects on the superconducting properties of MgB2 bulks were investigated. The density of bulk samples increased with the rise of sintering temperature and the density reached to the maximum value when the sintering temperature rose to 1000 degrees C. For the sample sintered at 1000 degrees C, the critical transition temperature (T-c)( )reached the highest value of 38.8 K despite the high content of MgB4 (30.62 wt.%). However, the critical current density (J(c)) did not increase with the increase in the density and T-c. The sample sintered at 700 degrees C maintained the high superconducting volume and had a small grain size, thus providing the best magnetic flux pinning force and J(r). An effective hot-pressing process to improve J(c) might be the way to prepare by further increasing the density of sintering samples at 700 degrees C.