Valences of Cu and Tl and chemical bond parameters in Tl xBa 2Cu yO 6+ δ, Tl 2Ba 2CaCu 2O 8, and Tl 2Ba 2Ca 2Cu 3O 10

Abstract

The valences of Cu and Tl and chemical bond parameters, that is, bond covalency and macroscopic linear susceptibility in Tl x Ba 2Cu y O 6+ δ , Tl 2Ba 2CaCu 2O 8, and Tl 2Ba 2Ca 2Cu 3O 10 have been calculated using a semi-empirical method. For Tl x Ba 2Cu y O 6+ δ , the results indicate that the average valences of Tl and Cu are between +2.0 and +3.0, indicating that part of Cu and Tl is in a state of +3.0. With the increase of oxygen content and Tl/Cu ( x/ y) ratios, the valence of Tl increases, while for the valence of Cu this trend is only observed for fixed Tl/Cu ratio samples. The valence of Tl changes more rapidly than that of Cu. For samples where both oxygen content and Tl/Cu ratio change, there exists an optimal valence of Cu and Tl for the highest T c. On the other hand, for fixed Tl/Cu ratio samples, the smaller the valences of Cu and Tl, the higher the T c. The bond covalencies of Ba–O, Cu–O (in CuO 2 layer), and Tl–O (the bond of Tl with the inserted oxygen between double TlO layers) are sensitive only to the Tl/Cu ratios, while those of the remaining Tl–O bonds and Cu–O (outside CuO 2 layer) are influenced by both. The macroscopic linear susceptibility tends to decrease with the increase of oxygen content and Tl/Cu ratios. Finally, Tl 2Ba 2CaCu 2O 8 and Tl 2Ba 2Ca 2Cu 3O 10 have also been investigated.