Annealing study on (Tl1−xHgx)2Sr2Ca2Cu3Oy and determination of its crystal structure by X-ray powder diffractometry Original Research Article

Nearly single-phase superconducting (Tl1−xHgx)2Sr2Ca2Cu3Oy samples were prepared by the high-pressure technique. As-prepared samples with x=0.35 and 0.65, with optimally nominal oxygen contents, were overdoped and show Tc of 103 and 80 K, respectively. Reducing treatments in Ar/H2 were found to be effective in increasing Tc up to 116 and 118 K for x=0.35 and 0.65, respectively. The increase in Tc is also accompanied by a small weight loss and an increase in the room temperature c-axis length, with both phenomena resulting from oxygen loss. The crystal structure of the sample with x=0.35 was determined by X-ray Rietveld refinements. This crystal belongs to a tetragonal system and has a space group of I4/mmm with a=3.8130(5) and According to the present refinement, the Tl site must be partially occupied by a lighter element, whereas the Ca site is occupied by a heavier one and the O(4) atom must shift from its ideal position 4e site (1/2,1/2,z) to the 16m site (x,x,z).