FeSe1-x samples have been prepared by a solid-state reaction in the Ar13% H2 gas flow. The samples sintered at 410°C were of the tetragonal PbO structure (β-phase), showing little trace of d-phase (hexagonal). However, the samples sintered at higher temperatures contained a fair amount of d-phase, which was unable to be eliminated completely by subsequent annealing at r450°C for a prolonged period. Both M-T and R-T measurements showed that sintered samples of β-phase were superconducting with an onset Tc above 8.1 K. Thick films of FeSe1-x were grown on LaAlO3 substrates by liquid phase processing with SeSn as the flux. In contrast to the sintering, the filmsgrown around 910°C from the Sn-containing liquid had a pure β-phase. Although the phase diagram showed some solid solubility of Sn in FeSe, energy-dispersive X-ray spectroscopy failed to find Sn trace in the crystallized films, which showed a steeper superconducting transition at lower Tc of 6.0 K. To clarify whether the possible Sn contamination caused the drop of Tc, FeSe 1-x:5% Sn samples were sintered, which showed little change of T c from the pure β-FeSe1-x. The cause for the T c reduction of thick films remains unclear.
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