Structural Rearrangements in Fluorinated Cuprates

The cation position in the (Ao) layers can be jointly occupied by rare-earth and alkali-earth cations if A = Sr. The Cu cations have tetragonal pyramidal oxygen coordination. In contrast to the n = 1 member, in the stmcture of the second member there are two possible positions for extra anions in the tetrahedral interstices between the (RO) and (OR) layers and in the (Ao) layer, that will complete the Cu coordination to octahedron. The behaviour 

Ca results in the Sr2Ndo.2Cao 8CU2O5F compound with Tc = 85K. It is assumed that in these phases the fluorine anions are located in the NaCl-type blocks, forming the (SrF)(FSr) or (SrOo.5Fo.5)(Fo.50o.5Sr) layers. 

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