Ca substitution in RBa2Cu3O7-delta (R=Y, Er; delta<0.15): The influence on structure and superconductivity

We present a combined neutron and X-ray study of the effects of Ca doping in RBa2Cu3O7-delta (R=Y, Er). The structural effects observed by diffraction methods are correlated with the observed changes in T-c and interpreted in terms of ion size and charge effects. We deduce from bond valence sum calculations that the partial substitution for R3+ (R=Y, Er) with Ca2+ causes overdoping of the CuO2 planes. Inelastic neutron scattering has been used to study the low-energy crystal-field (CEF) excitations of Er3+ in Er1-xCaxBa2Cu3O7-delta (0 less than or equal to x less than or equal to 0.2). Due to Ca doping the CEF transition around 10.8 meV decomposes into two individual transitions whose spectral weights depend distinctly on the Ca doping level. We conclude that these substructures occurring due to Ca doping originate from different local environments of Er3+ due to a phase separation in the overdoped region.