Structure and Superconductivity of FeSe1 - x and FeTe1 - ySey Crystals: Dependence on the Synthesis Methods, Starting Composition, and Growth Conditions
D.J. Gawryluka, J. Fink-Finowickia, A. Wiśniewskia, R. Puźniaka, V. Domukhovskia, R. Diduszkoa, b and M. Berkowskia
aInstitute of Physics, Polish Academy of Sciences, al. Lotników 32/46, PL-02-668 Warsaw, Poland
bInstitute of Electronic Materials Technology, Wólczyńska 133, PL-01-919 Warsaw, Poland
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Syntheses of superconducting iron chalcogenides FeSe1 - x (x = 0-0.15) and FeTe1 - ySey (y = 0.3-0.55) were performed. Superconducting phase of iron selenide was obtained by the solid-state reaction and from liquid phase. The highest values of critical temperature (Tc = 8.2-8.7 K) exhibit FeSe1-x obtained by the crystallization from a melt with excess of iron less than 1 mol%. The samples from a melt contain up to 78% of tetragonal phase, as estimated by the X-ray diffraction. Lattice parameters and unit cell volume for the samples exhibiting highest Tc and sharpest transition to superconducting state are limited to narrow range, with c/a ratio close to 1.469. The samples with excess of selenium contain higher amount of hexagonal phase than stoichiometric one. Superconducting single-crystalline samples of FeTe1 - ySey (up to 100% of tetragonal phase) were obtained using Bridgman's method. When y value increases, the volume of unit cell decreases. The critical temperature Tc changes from ≈ 11.5 K for y ≈ 0.3 to ≈ 14.7 K for y ≈ 0.5.
DOI: 10.12693/APhysPolA.118.331
PACS numbers: 61.05.cp, 74.25.Ha, 74.62.Bf, 74.70.Xa, 81.10.Fq