PREPARATION, ELECTRIC-CONDUCTIVITY AND CRYSTAL-STRUCTURE OF (SR2-XBAX)CUO2+Y(CO3)Z

(Sr2-xBax)CuO2+y(CO3)z solid solutions with 0 less-than-or-equal-to x less-than-or-equal-to 1.75 were synthesized at 1173 K under atmospheres of O2-CO2 gases (partial pressures of CO2(P(CO2)) 10(1)-10(4) Pa). The lattice parameters of the solid solutions increased with increasing Ba content x from a'=5.5186 (1) and c'=7.497 (1) angstrom (x=0; a'=a/square-root 2 and c'=c/2) to a=5.6760 (1) and c=7.9276 (2) angstrom (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 2.0X10(-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.