Abstract
The structure and superconductivity in the single CuO layer bismuth (2021) system can be stabilized also by the doping of Na 1+ ions. Contrary to the La-doped Bi 2 (Sr,La) 2 CuO 6+δ system with T c enhancement up to 35 K. T c remains around 10 K for the Na-doped Bi 2 (Sr 2-x Na x )CuO 6+δ system (0.0 ≤ x ≤ 0.4). The variation of T c with the CuO bond length r CuO in the CuO layer for the Bi family which consists of the systems (Bi,Pb) 2 Sr 2 CuO 6+δ , Bi 2 (Sr,Na) 2 CuO 6+δ , Bi 2 (Sr,La) 2 CuO 6+δ and (Bi,Pb) 2 (Sr,La) 2 CuO 6+δ indicates an optimum r CuO value of 1.906-1.913 Å with maximum T c of 35 K for these Bi(2021) compounds. © 1991.