Structural and conductivity properties of Bi(0.775)Ln(0.225) O-1.5 oxide conductors (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) with rhombohedral Bi-Sr-O type

This paper deals with structural and conductivity properties of the dimorph ic Bi(0.775)Ln(0.225)O(1.5) (Ln = La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) hexagonal structure layer phases with rhombohedral Bi-Sr-O type, The evolutions, ver sus Ln(VI)(3+) radius, of cell parameters, thermal expansion coefficients, electrical properties (conductivity and activation energy), and structural characteristics determined from Rietveld powder structure refinements, sugg est two different domains (La-Sm) and (Gd-Dy), with the intermediate Eu sam ple, thus possibly characterizing two kinds of ordering in the mixed cation ic layer. The best conductivity properties obtained for Bi0.775La0.225O1.5 (sigma(400 degrees C) = 10(-3) S cm(-1) with E-a = 0.8 eV) are discussed an d justified. (C) 1999 Academic Press.