Solid state synthesis and characterization of bulk β-FeSe superconductors

Polycrystalline FeSe0.88 was synthesized by solid-state reaction method in sealed quartz tube at different heat heating cycles. The identification and characterization of FeSe0.88 samples were determined by X-ray Diffraction (XRD), Scanning Electron Microscope (SEM) and Energy Dispersive X-ray Spectroscopy (EDX). The electrical transport, magnetic and thermal transport properties of the obtained samples were also investigated. The results showed that the sensitivity of resistivity and magnetic susceptibility depends on heating cycles while the structural formation of samples does not. The upper critical field Hc2(0) has been determined with the magnetic field parallel to the sample surface and yielding a maximum value of 23.2 T. At the zero field coherence length, ξ, value was calculated to be 3.33 nm. Calculated μ0Hc2(0)/kBTc rate indicated comparably higher value (3.17 T/K) than the Pauli limit (1.84 T/K) and obtained results were suggested unconventional nature of superconductivity in our samples.