Synthesis of Bulk FeTeSe ( x = 0.1−0.5) at Ambient Pressure.

In this study, polycrystalline samples with nominal composition FeTeSe ( x=0.1−0.5) were synthesized by solid-state reaction method at ambient pressure. In order to minimize oxidation, argon gas flow was maintained throughout the heat treatment. The phase formation of FeTeSe samples was checked by X-ray diffraction (XRD). The polycrystalline FeTeSe samples were indexed to a tetragonal structure with space group of P4/nmm. The lattice parameters a- and c-axes shrink significantly with the substitution of Se. As shown by the scanning electron microscope (SEM) images, the samples developed a plate-like grain structure gradually with the increase of Se concentration. Measurements of temperature dependence of magnetic moment showed that the onset of superconducting transition temperature, T, increased with Se concentration. The T is about 10.6 and 13.5 K for x= 0.1 and 0.5, respectively. All the samples exhibit ferromagnetic behavior asshown by the field-dependent magnetization measured at room temperature. [ABSTRACT FROM AUTHOR]