Name: KELLY CORDEIRO MIRANDA
Publication date: 20/03/2017
Advisor:
Name |
Role |
|---|---|
| CARLOS AUGUSTO CARDOSO PASSOS | Advisor * |
Examining board:
| Name |
Role |
|---|---|
| CARLOS AUGUSTO CARDOSO PASSOS | Advisor * |
| JOSÉ LUIS PASSAMAI JUNIOR | External Examiner * |
| MÁRCIO DE SOUSA BOLZAN | External Examiner * |
| MARCOS TADEU DAZEREDO ORLANDO | Internal Examiner * |
Summary: Superconducting polycrystalline samples of SmBa2Cu3O7−d (Sm123) were prepared by the solid-vapor reaction technique from samarium, copper and barium carbonate oxides. The reagents were macerated in grams of agate for one hour and pressed under a 3tonne uniaxial pressure. Then, the samples were submitted to different heat treatments (Calcination Process) whose temperatures were 850◦C (sample A), 900◦C (sample B) and 930◦C (sample C), WHERE they remained for a period of 40 hours. After this, the samples were macerated, pastilled and submitted to a second heat treatment (Sintering Process). In this case, heating was carried out at a rate of 5 ◦ C / min to 900◦C and 2◦C / min until reaching the temperature of 1060◦C and remained at this level for 30 minutes. The oven was cooled to 520◦C WHERE it remained for 24 hours. The oxygen flow used was 10 bubbles / min (0,2cm3/s). In order to induce the formation of the orthorhombic crystal structure, all samples were thermally plotted with the same synthesis parameters, except for the temperature decrease ramp which was 1 ◦ C / min to the 500◦C plateau, WHERE it remained for 10 Hours and ending at 1 ◦ C / min to room temperature. The samples were characterized by X-ray powder diffraction (XRD), scanning electron microscopy (SEM) and magnetization. The results of XRD after the third heat treatment indicated compositions with superconducting phases that have two crystalline structures: tetragonal (>50%), orthorhombic (>24%) and some unidentified (<25%) peaks. In addition, the samples had the percentage of the tetragonal phase and samples B and C had an increase in the orthorhombic phase. Also through the results of XRD, it was possible to calculate the network parameters and it was verified that the sample B, had a smaller unit cell volume in the orthorhombic phase. Through the SEM images, the average size of the junction was obtained and it was found that the size of the junction increased with increase of the temperature used in the calcination process. The magnetization measurement indicated that sample B had better magnetic shielding. With the derivative method, the value of Tc and the transition width were found. Sample B had the highest value of Tc 39.1K and the lowest transition span (δT). This indicates that the sample B had a better homogeneous distribution of oxygen between the grains
