J. Gopalakrishnan et al., SUPERCONDUCTING THALLIUM CUPRATES OBTAINED BY SUBSTITUTION OF COPPER FOR THALLIUM IN THE DOUBLE-THALLIUM LAYER CUPRATE (T12212), Materials research bulletin, 29(4), 1994, pp. 369-376
A new series of superconducting thallium cuprates of nominal compositi
on, (Tl2-xCux)Ba2CaCu2O8 (0<x<1.0), where copper seems to substitute f
or thallium in T12212, is reported. These materials, which are synthes
ized at 920K-1120K in sealed silver tubes, exhibit T(c)s in the range
110-99K. The phases are metastable, decomposing at higher temperatures
(almost-equal-to 1150K) to a mixture of thallium cuprates, CuO and Ba
CuO2. Significantly, x = 1 member decomposes at 1150K to mixture of Tl
2223, CuO and BaCuO2. Chemical titrations involving oxidation of bromi
de ions reveal that the copper substituting for thallium in (Tl2-xCux)
Ba2CaCu2O8 most likely occurs in the III oxidation state for x less-th
an-or-equal-to 0.25 and in a mixed state (II, III) state for x>0.25.