Cationic Substitutions and Doping in the Series of Layered Perovskites Ln2Ba2Cu2Ti2O11 (Ln=La,Nd,Eu,Tb)

Abstract

Several cationic substitutions have been performed on the series of layered perovskites Ln2Ba2Cu2Ti2O11 (Ln = La, Nd, Eu, Tb). The substitution attempts of the Ln ions that we performed were not successful. On the other hand K could be substituted for Ba and Sc, Al, Co, Zn and Cu for Ti. Nevertheless we found in all case a spontaneous loss of oxygen taking place upon substitution. This oxygen stoichiometry readjustment is such that leaves the oxides effectively undoped. Several attempts at oxidations nder high pressures of oxygen have been made, resulting oxygenation and doping of La2Ba2Cu2.15Ti1.85O11. Nevertheless this oxide does not present signs of superconductivity down to 4 K due most likely to the long Cu---O bond distance in its structure. Some n-type substitutions were also tried.