Synthesis and crystal growth of Cs0.8(FeSe0.98)2: a new iron-based superconductor with Tc=27 K

We report on the synthesis of large single crystals of a new FeSe layer superconductor Cs-0.8(FeSe0.98)(2). X-ray powder diffraction, neutron powder diffraction and magnetization measurements have been used to compare the crystal structure and the magnetic properties of Cs-0.8(FeSe0.98)(2) with those of the recently discovered potassium intercalated system KxFe2Se2. The new compound, Cs-0.8(FeSe0.98)(2), shows a slightly lower superconducting transition temperature (T-c = 27.4 K) in comparison to 29.5 in (K-0.8(FeSe0.98)(2)). The volume of the crystal unit cell increases by replacing K by Cs-the c parameter grows from 14.1353(13) to 15.2846(11) angstrom. For the alkali metal intercalated layered compounds known so far, (K0.8Fe2Se2 and Cs-0.8(FeSe0.98)(2)), the T-c dependence on the anion height (distance between Fe layers and Se layers) was found to be analogous to those reported for As-containing Fe superconductors and Fe(Se(1-x)Ch(x)), where Ch = Te, S.