Otimização dos parâmetros de tratamento térmico da eletrocerâmica SmBa2Cu3O7-

Abstract

In this dissertation, samples of SmBa2Cu3O7-δ (Sm-123) polycrystalline ceramics were prepared through solid-vapor reaction. For this purpose, the mixture of Sm2O3, BaCO3, and CuO was mixed in the stoichiometric reaction of 1Sm:2Ba:3Cu. The tablets were made in a ceramics compaction matrix with the application of a 3.0 ton, single-axle pressure for 5 minutes. After that, they were subjected to thermal treatment in a horizontal isostatic tubular oven. To obtain the precursor in an open furnace, in the first thermal treatment (calcination) we used two isotherms 930 ºC and 960 ºC for 40 hours and cooling through the inertial thermodynamics of the furnace. After that, the samples were macerated, compacted once more, and subjected to a second thermal treatment (sintering) under a constant oxygen flow of 10 bubbles/min with isothermals of 960 ºC and 1060 ºC for 72 hours. Then the samples were cooled to 520 ºC through the furnace’s inertia at a rate of 5 ºC/min and sustained at that level for 24 hours. At that point, the same cooling parameters were used until reaching room temperature. The samples were characterized by X-ray diffraction techniques, electron scanning microscopy, energy dispersion spectroscopy, and apparent density determination by the Archimedes method. The diffractogram results indicated the predominance of the Sm-123 phase with two crystalline structures: tetragonal and orthorhombic. Besides, spurious phases resulted from incomplete reaction and/or excessive burning. It was observed that one of the samples, sample D, presented 62.5% of orthorhombic phase, 24.4% of tetragonal phase, and 13% of unidentified phases. The micrographs obtained by electron microscopy scanning indicated that the samples had an average grain boundary radius between 1.70 and 2.30 µm, except for sample M, which had a value of the order of 10.20 µm. Finally, the relative density measures indicated that they are dependent on the heat treatment process, and the results varied between 79% and 96% of the theoretical density. However, none of the samples showed a superconducting transition above 77 K. Thus, we conclude that the calcination treatments have a strong influence on the microstructure, phase formation, and density of the Sm-123 ceramic