Common Crystalline and Magnetic Structure of Superconducting A2Fe4Se5 (A = K, Rb, Cs, Tl) Single Crystals Measured Using Neutron Diffraction

Single-crystal neutron diffraction studies on superconductors A(2)Fe(4)Se(5), where A Rb, Cs, (Tl, Rb), and (Tl, K) (T-c similar to 30 K), uncover the same Fe vacancy ordered crystal structure and the same block antiferromagnetic order as in K2Fe4Se5. The Fe order-disorder transition occurs at T-S = 500-578 K, and the antiferromagnetic transition at T-N = 471-559 K with an ordered magnetic moment similar to 3.3 mu(B)/Fe at 10 K. Thus, all recently discovered A intercalated iron selenide superconductors share the common crystalline and magnetic structure, which are very different from previous families of Fe-based superconductors, and constitute a distinct new 245 family.