Semiconductivity in YBa_2-xSr_xCu₃O_y

Structural and electrical properties of YBa_2-xSr_xCU₃O_y prepared under ambient oxygen pressure were systematically investigated for 0≤x≤2.0. Samples with high Sr contents, x≥1.7, showed samiconductive properties with an activation energy of ∼150 meV at high temperature, T≥80 K. At low temperatures, T≤80 K, activation energy dropped to ∼3.00 and ∼0.85 meV for x = 1.7-1.8 and x = 1.9-2.0, respectively. It is argued that YSr₂Cu₃O_y is likely to have a tetragonal structure and that the disorder introduced by Sr substitution affects electrical conduction, which involves charge hopping between the CuO chains at high Sr contents.