Nd substitution effects in YBa2Cu4O8 prepared using a conversion reaction from Y1-xNdxBa2Cu3O7-delta and CuO

Synthesis, crystal structure and magnetic properties of samples with partia l substitution of Nd for Y in YBa2Cu4O8 are considered. The samples with no minal composition Y1-xNdxBa2Cu4O8 (x=0.0-0.75) were prepared using a solid state conversion reaction from Y1-xNdxBa2Cu3O7-8 and CuO using LiF as a flu x. The annealing was performed at 790 degrees C in a flowing oxygen atmosph ere. The products with x=0.0-0.5 showed thermal stability up to 660 degrees C in N-2(g) atmosphere revealing a single phase composition. The success o f the synthesis is considered in relation to the effective ionic size of th e Nd3+ ion. The crystal structures of the compounds are described on the ba sis of powder neutron diffraction measurements. The T-c values of the Nd su bstituted samples were noticeably lower than for the pristine YBa2Cu4Odelta . Possible reasons for the decrease in T-c are discussed on the basis of ca lculated values for hole concentrations in the Cu-O-2 planes obtained via t he BVS (bond valence sum) method, and on the basis of some Nd3+ ions being introduced at Ba2+ ion sites in the lattice. (C) 2000 Elsevier Science Ltd. All rights reserved.