N. H. Mohammed

Synthesis and electrical resistivity studies of Tl1−xPrxBa2Ca2Cu3O9−δ superconductors

Several high-temperature superconductor samples of the general composition Tl1−xPrxBa2Ca2Cu3O9−δ, with 0 ≤ x ≤ 0.3, have been synthesized by a single solid-state reaction. Within a narrow range of composition, x 0.2, the samples are almost single phase possessing a tetragonal unit cell similar to the Tl-1223 phase. The electrical resistivity exhibits a metallic behaviour for 0 ≤ x ≤ 0.2 above the transition temperature whereas it exhibits a semiconductor-like behaviour for x > 0.2. The normal electrical resistivity ρn is enhanced as the Pr content increases and the resistivity data, in the semiconductor regime, are well fitted according to the variable range hopping model. The transition temperature, determined from electrical resistivity measurements, decreases monotonically with x and the superconductivity disappears at around xc = 0.29. The depression in the transition temperature as Pr content increases is due to two different mechanisms involving hole filling or Cooper pairs breaking.