Abstract :
The effects of oxygen doping on the hole-carrying CuO2-layers in Tl2(Ba1−xSrx)2Ca2Cu3Oy were studied by combined chemical and valence analysis, Tc measurements and neutron diffraction. The highest Tc is characterized by an optimal excess oxygen content, Δy, dichotomizing the under- and over-doped regions for each Sr concentration. While the average Tl valence is close to 3.0 and independent of Δy, the average Cu valence shows a linear dependence with Δy. An increase of the flatness of the CuO2 plane, characterized by the O(2)–Cu(2)–O(2) bond angle of ∼176°, was observed at the optimal Δy.
