Effect of fabrication parameters on structural andelectrical properties of MgB2 sample

In this thesis, the effects of annealing temperature on the microstructure, electrical and magnetic properties of MgB2 samples during the annealing process were investigated. For this purpose, 4 different samples (S650, S750, S850 and S950) were produced by pressing MgB2 in powder form into bulk and annealing at 650°C, 750°C, 850°C and 950°C for 1 hour. In order to compare the produced samples, XRD, SEM, R-T, R-H and AC susceptibility measurements were taken. When XRD measurements were examined, in addition to obtaining information about their purity, crystal structure parameters a and c (crystal structure size) were calculated. By examining the surface structures from SEM measurements, particle sizes and material densities were calculated. The temperatures at which MgB2 samples, a typical Type-II superconductor, started to become superconducting (Tonset) and completely superconducting (Toffset) under different external magnetic fields were determined from the measurements of the change in resistance with respect to temperature. In these measurements, the Hc1 magnetic fields, at which temperatures the external magnetic fields we determined, began to deteriorate the superconductivity, and the HC2 magnetic fields, which completely deteriorated, were determined. In the R-H measurements, the curves of the variation of the resistance with externally applied DC magnetic field at constant temperature were obtained. From these curves, the HC2 magnetic fields, which are completely disrupted by superconductivity at constant temperature, were found. Tonset and Toffset temperatures were determined from the curves obtained from AC-Susceptibility measurements, and Jc intergranular critical current densities were calculated. As a result of all measurements and calculations; The increase in annealing temperature up to 850°C improves the microstructure properties such as grain size, surface density, intergranular bonding, and worsens after this temperature, the critical temperature, critical current density and critical magnetic fields are better in the S850 sample, all measurements are compatible and consistent with each other, and showed that 850°C temperature in heat treatment of all measurements improved the microstructure, surface morphology, superconductivity and magnetic properties of the MgB2 sample.