EFFECTS OF FLUORINE SUBSTITUTION IN SUPERCONDUCTING TL2BA2CUO6+ -DELTA/

The fluorine substituted thallium based 2 2 0 1 phase samples were fab ricated with starting compositions 0.95Tl(2)O(3) + 0.1SnO(2) + (2-x)Ba O2 + xBaF(2) + CuO. Mossbauer and X-ray spectra were used as a study o f the role played by fluorine. All samples show a near 2 2 0 1 pure ph ase. The best fluorine substituted sample has T-c (onset) of 100 K and the T-c(R = 0) of 97 K. The Mossbauer absorption area varies, paralle l to T-c, with the fluorine content and reaches a maximum absorption n ear x = 0.6, which indicates that fluorine could have replaced oxygen in the crystal lattice sites and thus does not rule out the presence o f a phonon superconducting mechanism. (C) 1997 Elsevier Science Ltd.