Ma. Subramanian, STABILIZATION OF SUPERCONDUCTING PHASES IN THALLIUM-BARIUM-COPPER OXIDE SYSTEM BY FLUORINE SUBSTITUTION [TLBA2CUO5-XFX], Materials research bulletin, 29(2), 1994, pp. 119-125
Partial substitution of oxygen by fluorine in TlBa2CuO5 has been achie
ved by heating Tl2O3, BaO2, BaO and CuO under one kbar external pressu
re using TlF as a source for fluorine. A single phase region exists fo
r 0.1 less-than-or-equal-to x less-than-or-equal-to 0.5 and the X-ray
powder diffraction data indicated a tetragonal structure (space group:
P4/mmm) for all the compounds. The in-plane Cu-0 distance calculated
from the a-lattice parameter showed a systematic increase as x was var
ied from 0.1 to 0.5. This is due to an increase in the formal oxidatio
n state of copper as F1- substitutes for O2- in the 1201-type structur
e. The c-lattice parameter also showed a slight increase, as the fluor
ine content in the reaction mixture is increased. Superconductivity is
observed for x values within the range 0.1 to 0.6 with transition tem
peratures in the range 35-75 K.