Bi-M/M'-O (M,M' equals alkaline-earth) and Bi-M/M'-Pb-O: New members of the dimorphic rhombohedral Bi-Sr-O type anionic conductors family

Significant domains of the dimorphic Bi-Sr-O rhombohedral type phases have been evidenced in Bi-M/M'-O and Bi-M/M'-Pb-O materials (M, M' = Ca, Sr, Ba). Their stability, their structural and electrical conductivity properties have been investigated. Sr or Ba for Ca substitution in Bi0.75Ca0.125Pb0.125O1.374 allows the preservation of the beta(1) high temperature form, by air quenching, within the limits 0.2 less than or equal to Sr/(Sr + Ca) less than or equal to 0.8 and 0.1 Ba/(Ba + Ca) less than or equal to 0.6. In absence of lead, the occurrence of beta(2) or beta(1) domain has been investigated, in particular Bi-Sr/Ba-O samples. It is possible to quench beta(1) for bismuth rich compositions, but the extent of the corresponding domain is related to the quenching conditions: Bi0.844Sr0.156(1-x)Ba0.156xO1.422 samples adopt the stable low temperature beta(2) type. Their thermal behaviour investigation has pointed out the occurrence of a cationic order, which is confirmed by a single crystal X-ray diffraction study.