The role of charge carrier concentration in Tl-1234

Three (Tl0.5Pb0.5)Sr1.6Ba0.4Ca3Cu4Oy (Tl-1234) samples with different charg e carrier concentrations were investigated. One sample was air-annealed, th e second was annealed in O-2 flowing atmosphere and the third was annealed in air but one-quarter of the Cu content was obtained from CuF2 rather than CuO. The first two samples were superconducting with onset T-c = 128 K whi le the third was non-superconducting An information about the charge carrie r state of samples 1 and 2 was obtained from the normal state resistivity. XRD analysis shows that the three samples have the expected structure and l attice parameters for the Tl-1234 and confirms that fluorine (F) enters the structure of Tl-1234 phase and affects its charge carrier concentration. T he high fluorine content in the third sample greatly changed the hole conce ntration in the Cu-O planes and destroyed the superconductivity in the Tl-1 234 phase. (C) 2000 Elsevier Science B.V. All rights reserved.