Non-Stoichiometry and Complex Defects in the Structure of R-Ba-Cu-O Single Crystals Determined by Neutron Diffraction
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NON-STOICHIOMETRY AND COMPLEX DEFECTS IN THE STRUCTURE OF R-BA-CU-O SINGLE CRYSTALS DETERMINED BY NEUTRON DIFFRACTION P. SCHWEISSa+b, Ph. GALEZc, G. COLLINC+d and F. MARUCCOe a) Laboratoire LUon Brillouin, C.E.N.Saclay, 91191 Gif sur Yvette France b) Kernforschungszentrum Karlsruhe, INFP, D-7500 Karlsruhe and Institut ftir Mineralogie, Lahnberge, D-3550 Marburg/Lahn F.R.G. c) C.P.C.M., DPhG, C.E.N.Saclay, 91191 Gif sur Yvette, France d) Laboratoire de Physique des solides, U.R.A. 02 C.N.R.S., Bt. 510, Universit6 Paris-Sud, 91405 Orsay, France e) Laboratoire des Solides non-stocchiom6triques, Bt 415, Universit6 Paris-Sud, 91405 Orsay, France ABSTRACT The crystal structure of several RBa2 Cu 3 _v0 6 +z (R=Y,Ho) crystals are investigated by neutron diffraction using an exact solution for the twinned orthorhombic samples. For an oxygen concentration >0.35 in the chains, the structure is orthorhombic due to an exclusive occupancy of the 0(4) site. A systematic and variable copper deficiency is observed on the Cu(1) site leading to a correlated defect on the chain oxygen 0(4) and on the bridging oxygen O(1). Due to the presence of these defects, a transverse disorder is observed for the highest oxygen content with a residual occupancy of the forbidden 0(5) site. INTRODUCTION The outstanding structural feature of the YBa 2 Cu3 O6 +z (0
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