Structural and Conductivity Properties of Bi0.775Ln0.225O1.5Oxide 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 dimorphic Bi0.775Ln0.225O1.5(Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy) hexagonal structure layer phases with rhombohedral Bi-Sr-O type. The evolutions, versusLn3+VIradius, of cell parameters, thermal expansion coefficients, electrical properties (conductivity and activation energy), and structural characteristics determined from Rietveld powder structure refinements, suggest two different domains (La-Sm) and (Gd-Dy), with the intermediate Eu sample, thus possibly characterizing two kinds of ordering in the mixed cationic layer. The best conductivity properties obtained for Bi0.775La0.225O1.5(400°C=10-3S cm-1withEa=0.8 eV) are discussed and justified.