CHARACTERIZATION OF INCOMMENSURATE BI2+XSR2-XCUOZ BY X-RAY-POWDER DIFFRACTION AND OXYGEN-CONTENT DETERMINATIONS

The composition-temperature stability region of the solid solution Bi2+xSr2-xCuOz, phase R, has been determined. At 800°C, and at melting temperatures, with a supercell vector q*given by q*=n δb*-nεc*, where δ=0.21, ε=0.55, for x=0.30 and n=1, 2 …. Both a and ε increased with x, c decreased with x and δ was independent of x. The excess oxygen content, α, was determined to be (0.18±0.02) by citrate iodometry and was independent of x. The total oxygen content z, given by z=6+x/2+α, was confirmed to be 6.33±0.04, for x=0.30, by hydrogen reduction thermogravimetry. © 1990 IOP Publishing Ltd.