Influence of Heat Treatment on the Anelastic Properties of MgB₂

Abstract

The discovery of the superconductivity of MgB2 was of great importance, because this material is one of the few known binary compounds and has one of the highest critical temperatures (39° K). As MgB2 is a granular compound, it is fundamentally important to understand the mechanisms of the interaction of the defects and the crystalline lattice, in addition to the eventual processes involving the grain boundaries that compose the material. In this sense, the mechanical spectroscopy measurements constitute a powerful tool for this study, because through them we can obtain important information about phase transitions, the behavior of interstitial or substitutional elements, dislocations, grain boundaries, diffusion, instabilities, and other imperfections of the lattice. For this paper, the samples were prepared using the PIT method and were characterized by density, X-ray diffraction, scanning electron microscopy, electric resistivity, magnetization, and mechanical spectroscopy. The samples were measured in their as-cast condition and after an ultra-high-vacuum heat treatment. The results showed complex spectra, in which were identified relaxation processes due to dislocation movement, interaction among interstitial elements and dislocations, auto-diffusion, and movement of grain boundaries. Some of these processes disappeared with the heat treatment.

Mechanical Spectroscopy of MgB2 Containing Sic / Spektroskopia Mechaniczna MgB2 Zawierającego Sic

“…Silva and Grandini [12] reported the internal friction in pure MgB 2 , in the as-cast state and after heat treatment in vacuum, and observed a broad thermally activated relaxation effect composed of almost three relaxation processes that were attributed to the interaction between point defects and dislocations, hydrogen mobility along the dislocation line, and the migration of magnesium atoms. In the case of the annealed sample, some relaxation processes disappeared after the heat treatment.…”