ACTA

Structure and Superconductivity of FeSe_{1 - x} and FeTe_{1 - y}Se_y Crystals: Dependence on the Synthesis Methods, Starting Composition, and Growth Conditions

D.J. Gawryluk^a, J. Fink-Finowicki^a, A. Wiśniewski^a, R. Puźniak^a, V. Domukhovski^a, R. Diduszko^{a, b} and M. Berkowski^a
^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 FeSe_{1 - x} (x = 0-0.15) and FeTe_{1 - y}Se_y (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 (T_c = 8.2-8.7 K) exhibit FeSe_1-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 T_c 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 FeTe_{1 - y}Se_y (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 T_c 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