Substitution of lead for bismuth in the 2201-type oxide Bi 2BaLaCuO 6+δ

Abstract

The study of the substitution of bismuth in the 2201 bismuth barium cuprate allowed two isostructural phases Bi 2− x Pb x BaLaCuO 6+δ to be isolated for 0 ⩽ x ⩽ 1.40. The bismuth-rich phases (0 ⩽ x < 0.4) exhibit a modulated structure similar to that of B 2Sr 2CuO 6+δ, with a period along b ranging from 3.8 ( x = 0) to 4.2 ( x = 0.8). The lead-rich phases (0.8 ⩽ x ⩽ 1.4), do not exhibit any modulation of the structure, but are characterized by the existence of weak superstructure spots. The transition from the modulated to the non-modulated structure is accompanied by a dramatic increase of the c parameter of the orthorhombic oxides (5.4 × 5.4 × 24 Å 3). This evolution is interpreted in terms of the stereoactivity of the 6 s 2 lone pair of Bi(III) and Pb(II) and of the formation of anionic vacancies.