Nd substitution effects in YBa2Cu4O8 prepared using a conversion reaction from Y1−xNdxBa2Cu3O7−δ and CuO

Abstract

Synthesis, crystal structure and magnetic properties of samples with partial substitution of Nd for Y in YBa2Cu4O8 are considered. The samples with nominal composition Y1−xNdxBa2Cu4O8 (x=0.0–0.75) were prepared using a solid state conversion reaction from Y1−xNdxBa2Cu3O7−δ and CuO using LiF as a flux. The annealing was performed at 790°C in a flowing oxygen atmosphere. The products with x=0.0–0.5 showed thermal stability up to 660°C in N2(g) atmosphere revealing a single phase composition. The success of the synthesis is considered in relation to the effective ionic size of the Nd3+ ion. The crystal structures of the compounds are described on the basis of powder neutron diffraction measurements. The Tc values of the Nd substituted samples were noticeably lower than for the pristine YBa2Cu4O8. Possible reasons for the decrease in Tc are discussed on the basis of calculated values for hole concentrations in the Cu–O2 planes obtained via the BVS (bond valence sum) method, and on the basis of some Nd3+ ions being introduced at Ba2+ ion sites in the lattice.