On the noncubic layered structure of KnBamBim+nOy superconducting oxides

Superconducting K n Ba m Bi m + n O y (T c 20-32 K) crystals grown by electrolysis from KOH-Ba(OH) 2 -Bi 2 O 3 melt have been studied using electron diffraction (ED) and high-resolution electron microscopy (HREM). The structure is found to be cubic, layered, and noncentrosymmetric (space group P4mm) with the unit cell parameters a ≅ a p , c ≅ 2a p (a P is the unit cell parameter of perovskite ABO 3 ); barium and potassium ions are ordered.