Effect of synthesis route on the structure of Nd3−xBa3+xCu6O14−2δ (x=0,1) system: a neutron diffraction study

Structural studies on Nd3−xBa3+xCu6O14−2δ with 0≤x≤1 were carried out by Rietveld refinement procedure using neutron diffraction data. The composition x=1 was prepared both by the solid-state method and the nitrate-decomposition method. Quantitative multiphase analysis coupled with variation in the method of synthesis has shown conclusively that Nd did substitute for Ba even in a stoichiometric composition NdBa2Cu3O7−δ, irrespective of the method of synthesis. The fractional atomic substitution of Nd at the Ba site has been determined to be about 15%. The composition x=0, synthesised by the nitrate-decomposition method, has been found to be tetragonal with the space group P4/mmm. Nd has been found to substitute for Ba according to Nd(Ba0.75Nd0.25)2Cu3O7−δ and no random distribution of cations has been found along the c-direction. The observed tetragonality has been attributed to the additional oxygen taken into the basal (001) plane due to the substitution of trivalent Nd at the divalent Ba site.