The structural parameters of the superconductor (Ba0.633Nd0.367)2(Nd0.675Ce0.325)2Cu3O8+z (z≈0.91) were refined by the Rietveld analysis of TOF neutron powder diffraction data. This oxide belongs to a new family of solid solutions (Ba1-xLnx)2(Ln1-yCey)2Cu3O8+z (Ln=Nd, Sm, Eu and Gd). It has a body-centered tetragonal structure with space group I4/mmm and lattice constants a=0.38747(4) nm and c=2.8599(3) nm. Its structure can be derived by stacking tetragonal Ba2YCu3O6+z-and Nd2CuO4-type slabs alternately along the c-axis; they are jointed through two-dimensional hole-doped CuO2 sheets. Each Cu cation on the CuO2 sheet is coordinated to five oxide ions in a distorted square-pyramidal configuration. The Ba2YCu3O6+z-type slab accommodates Ba(Nd) atoms, whereas each Nd(Ce) atom in the Nd2CuO4-type slab has four short and four long Nd(Ce)-O bonds. Cu and O atoms within the Ba2YCu3O6+z-type slab are considerably displaced from ideal positions. An O site between two Ba(Nd)O sheets is highly deficient (occupancy: 0.114), as is observed in corresponding oxygen sites in the tetragonal structures of Ba2YCu3O6+z (z<0.5) and Ba2-xLn1+xCu3O7±z (Ln=La, Pr, Nd, Sm and Eu). Bulk superconductivity is induced by intercalating a sufficient amount of O at this position to increase the concentration of (Cu-O)+ holes on the CuO2 sheet.
ASJC Scopus subject areas
- Electronic, Optical and Magnetic Materials
- Condensed Matter Physics
- Energy Engineering and Power Technology
- Electrical and Electronic Engineering