The effect of Sr substitution on the structure and superconducting properties of Tl 2(Ba 2-xSr x)Ca 3Cu 4O 12
The four cuprate layer superconductor Tl 2Ba 2Ca 3Cu 4O 12 has been synthesised with Sr partially replacing Ba giving samples of stoichiometry Tl 1.5(Ba 2-xSr x)Ca 3.5Cu 4O 12 for x up to 0.3. X-ray diffraction data show single superconducting phase materials with significant reductions in the c-lattice parameter for increasing Sr content. The spacing between the central Cu1-Cu1 planes is observed to decrease whilst the outer Cu1-Cu1 distance increases with higher Sr contents. These variations in the cuprate layer spacings and proximity of the thallium oxygen planes to the copper layers, which occur as a function of changing Sr content, have been correlated with the superconducting properties. Values of T c remained almost constant around 115 K, however, the susceptibility increased with increasing Sr levels.