Synthesis, crystal and magnetic structure of iron selenide BaFe2Se3 with   possible superconductivity at Tc=11K
  We report on synthesis of single crystals of BaFe2Se3 and study of their crystal and magnetic structures by means of synchrotron single crystal X-ray and neutron powder diffraction. The crystal structure has orthorhombic symmetry and consists of double chains of FeSe4 edge connected tetrahedra intercalated by barium. Below 240 K long range block-spin checkerboard antiferromagnetic (AFM) order is developed. The magnetic structure is similar to one observed in A0.8Fe1.6Se2 (A=K, Rb or Cs) superconductors. The crystals exhibit a transition to the diamagnetic state with an onset transition temperature of Tc ~11 K. Though we observe FeSe as an impurity phase (<0.8% mass fraction) the diamagnetism unlikely can be attributed to the FeSe-superconductor which has Tc\approx8.5K. 
A. Krzton-Maziopa, E. Pomjakushina, V. Pomjakushin, D. Sheptyakov, D.   Chernyshov, V. Svitlyk and K. Conder
cond-mat.supr-con cond-mat.mtrl-sci cond-mat.str-el