ON THE CRYSTALLOCHEMISTRY OF THE BINARY BISR3OX PHASE

Phase relations prevalent at 850-degrees-C in the Bi2O3-SrO system (1.5 less-than-or-equal-to Sr:Bi less-than-or-equal-to 5.5) in air have been reinvestigated in order to clarify the chemical nature of the BiSr3Ox phase. On the basis of analytical determinations of the average valence of bismuth in samples tested and their densities, it has been found that BiSr3Ox is a compound which originates from the Bi2O5-SrO system (full chemical formula BiSr3O5.5) and is not a real constituent of the binary system with Bi3+. Investigation of the latter under free oxygen access results in unintentional penetration of part of the Bi2O3-SrO-Bi2O5 ternary system in which mutual relations between appropriate phases of both Bi binary systems are present and can be identified as three- or two-phase regions of coexistence (e.g. Bi5+Sr3O5.5 + Bi23+Sr3O6), misleadingly considered until now to occur in the pure Bi2O3-SrO system. The identity of the crystal structures of BiSr3O5.5 and BiNdSr2O6 has not been confirmed.