The effect of long-term exposure at room temperature on the thermal conductivity of the FeSe superconductor in the normal state

The temperature dependence of the thermal conductivity of the iron-based FeSe0.94 superconductor sample has been studied in the range of 4.2-200 K after long-term exposure for 7 years. The temperature dependence of thermal conductivity is predominantly phonon. This dependence was approximated taking into account phonon scattering by the boundaries of the sample, as well as scattering by dislocations, point defects, and phonon-phonon scattering. When comparing the parameters of this approximation with similar parameters for literature data for a freshly prepared polycrystalline sample, it turned out that long-term exposure led to a significant increase in all parameters. That is, long-term exposure causes a significant increase in the number of dislocations, and point defects and intensifies phonon-phonon scattering. For both samples, we found no effect of the structural phase transition at T approximate to 75 K from the tetragonal phase into the orthorhombic one on the thermal conductivity.