Phase relations and structure-properties correlations in Fe(S,Se,Te)

Three series of polycrystalline samples with nominal compositions Fe1.02TeySe1−y−xSx (y = 0.3, 0.4, 0.6 and 0 ≤ x ≤ 0.7) have been synthesized and studied by means of the X-ray diffraction, scanning electron microscopy, electrical resistivity and magnetization measurements. Together with the tetragonal superconducting phase, all the samples have been found to contain a hexagonal phase of the NiAs-type; and the increase in sulfur content leads to a redistribution of various chalcogens between phases due to the difference in solubility limits and variations of the chemical compositions and volume fractions of these phases. The sulfur for selenium substitution in Fe1.02TeySe1−y−xSx results in a growth in the average interlayer distance in the superconducting tetragonal phase because of its enrichment by tellurium and depletion in sulfur; while the hexagonal phase becomes enriched by sulfur and depleted in tellurium with increasing sulfur content in the samples. It has been shown that in the Fe(Te,Se,S) materials with ternary mixture of chalcogens, the variation of the critical superconducting temperature correlates with the change in the average interlayer distance in the tetragonal structure as in other FeSe-based materials.