Pressure effect on superconductivity in FeSe0.5Te0.5

Due to the simple layered structure, isostructural FeSe and FeSe0.5Te0.5 are clue compounds for understanding the principal mechanisms of superconductivity in the family of Fe-based superconductors. High-pressure magnetic, structural and Mossbauer studies have been performed on single-crystalline samples of superconducting FeSe0.5Te0.5 with Tc = 13.5 K. Susceptibility data have revealed a strong increase of Tc up to 19.5 K for pressures up to 1.3 GPa, followed by a plateau in the Tc(p) dependence up to 5.0 GPa. Further pressure increase leads to a disappearance of the superconducting state around 7.0 GPa. X-ray diffraction and Mossbauer studies explain this fact by a tetragonal-to-hexagonal structural phase transition. Mossbauer parameters of the non-superconducting high-pressure phase indicate less covalency of FeSe bonds. Based on structural and susceptibility data, we conclude about a common character of Tc(p) diagrams for both FeSe and FeSe0.5Te0.5 superconductors.