Preparation, electric conductivity and crystal structure of (Sr_2-xBa_x)CuO_2+y(CO₃)_z

(Sr_2-xBa_x)CuO_2+y(CO₃)_z solid solutions with 0≤×≤1.75 were synthesized at 1173 K under atmospheres of O₂-CO₂ gases (partial pressures of CO₂(P(CO₂)) 10¹-10⁴ Pa). The lattice parameters of the solid solutions increased with increasing Ba content x from a′ = 5.5186 (1) and c′ = 7.497 (1) Å (x = 0; a′ = a √2 and c′ = c 2) to a = 5.6760(1) and c = 7.9276(2) A ̊ (x = 1.75). The average Cu valence determined from iodometric titration changed from 2.010 (x = 0) to 2.043 (x = 1.75). The electric conductivity of the samples increased from 2.0 × 10^-1 to 5.0 S cm^-1 with increasing x at 290 K. All samples showed semiconducting behavior and no superconducting transition at temperatures down to 12 K The crystal structures of the solid solutions with x = 1.00 and x = 1.75 were refined by means of Rietveld analysis for neutron powder diffraction data. There was a deficiency of about 12% of the C atoms in the solid solution with x = 1.75. Excess oxygen atoms which may dope holes into the CuO₂ sheets were found at the carbonate deficient sites.