Enhancement of superconductivity and structural phase transitions under pressure in FeTe0.89S0.11

Abstract

The ternary iron chalcogenide, FeTe0.89S0.11 is a prominent member of the family of Fe-based superconductors with an ambient pressure Tc of around 8K and a simple structure formed by layers of edge-sharing distorted tetrahedra separated by a van der Waals gap. Upon compression to 6GPa, the Tc increases monotonically to 11K. The superconductivity disappeared at about 6GPa which was correlated to a softening of a Raman mode. High-resolution synchrotron X-ray diffraction shows that the FeTe0.89S0.11 started to transform from the monoclinic phase described by space group Cm to a disordered triclinic phase described by space group P1 at around 10GPa (theoretical) - 14GPa (experimental). Due to the phase transition the studied material transforms from a layered compound to a polymer, which is accompanied by a volume collapse of 4.65%, indicating a discontinuous first-order phase transition. The disappearance of Raman modes, along with pressure independent resistivity, and ab initio calculations results support the structural and electronics phase transition. According to our results Fe(Te,S) may be useful for future high-field power applications being formed of relatively inexpensive and nontoxic elements.