Optimum Heat Treatment Conditions Determination for Mg-Diffused MgB₂

Abstract

MgB2 superconducting pellets were synthesized by the Mg diusion method. Dierent heat treatment temperatures and times were applied for synthesis to determine optimum conditions. The phase structure of the samples was investigated by X-ray diraction measurements. MgB2 lattice parameters, MgO fractions, and crystal sizes were calculated. It was observed from the scanning electron microscope images that the grains were well connected and the grain sizes were homogeneous after heat treatment at 650 • C and 12 h. As a result of magnetization measurements, it was determined that the critical temperature of the samples that were heat-treated at 650 and 700 • C for 6 and 12 h showed close values, and the transition intervals were sharp. The critical current density values calculated according to the Bean model were found to be around 10 4 A/cm 2 for 625 • C samples and increased to 10 5 A/cm 2 for 650 and 700 • C samples. The highest critical current density value under 0 T at 20 K was obtained as 1.58 × 10 5 A/cm 2 for the 700 • C for 6 h sample. It was determined that the irreversibility eld values determined according to the 100 A/cm 2 criterion were close for 650 and 700 • C heat treatments. The pinning mechanism analyzed by the Dew-Hughes approach was detected as grain boundary pinning in 650 and 700 • C samples. It was shown that the minimum temperature for the heat treatment to be applied for the Mg diusion method should be 650 • C, and the extended heat treatment duration made no serious dierence.