Studies of microstructure and ruthenium valence in the ruthenocuprates Pb₂RuSrCu₂O₈Cl and (Ru,M)Sr₂GdCu₂O₈(M=Sn,Nb)

Ruthenocuprate microstructurcs and Ru valences have been studied. Electron microscopy reveals short-range order of the RuO6 octahedra rotations into a root2a x root2a x c supercell in Pb2RuSr2Cu2O8Cl. However, reanalysis of neutron diffraction data gives no significant difference between the populations of the rotation states, showing that the coherence length is very short (< 100 Angstrom). The Ru valence estimated from the XANES spectrum of Pb2RuSr2Cu2O8Cl is similar to5, in keeping with the physical properties of this material which show that there is essentially no Ru-Cu charge transfer. The Ru valence in doped Ru1-xMxSr2GdCu2O8 (M = Sn, Nb) is similar to4.8 in all samples, verifying a previous rigid band analysis of the charge distribution in these materials. (C) 2003 Elsevier Inc. All rights reserved.