Effect of rare earth and alkaline earth substitutions in the superconductor RuA2RECu2O8 (RE=Gd,Eu,Nd,Pr; A=Ca,Sr,Ba): crystal structure and physical properties

For small rare earth ions (RE=Gd,Eu), single phase compounds are obtained with the typical ordered layered structure and no significant changes of physical properties. With large rare earth ions (RE=Nd, Pr), polyphase samples were obtained and the phases in equilibrium at the nominal composition RuSr2RECu2O8 were determined. In these cases, no ordered layered structure was observed. The disorder between Ru/Cu or Sr/RE is presumably due to the similar Ru/Cu and Sr/RE ionic sizes. Magnetization studies of these compounds are discussed. The effect of substituting Sr+2 with the smaller Ca+2 and larger Ba+2 is examined. The substitution with Ca+2 results in a complex mixture. We cannot confirm the previously reported formation of the layered RuCa2NdCu2O8. %RuRE1212. For Ba+2 substitution, a binary mixture Ba2RuNdO6-CuO is obtained. A different number and different types of phases in equilibrium are found with different alkaline earths (A=Ca,Sr,Ba) at the nominal RuA2NdCu2O8 composition. The variation in the mismatch of the A/Nd (A=Ca,Sr,Ba) size does not lead to the formation of an ordered layered RuA2NdCu2O8 compound