Characterisation of incommensurate Bi_2+xSr_2-xCuO_zby X-Ray Powder Diffraction and Oxygen Content Determinations

The composition-temperature stability region of the solid solution Bi_2+xSr_2-xCuO_z, 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.