Polymorphism of Bismuth Sesquioxide. II. Effect of Oxide Additions on the Polymorphism of Bi(2)O(3)

The effect of small oxide additions on the polymorphism of Bi(2)O(3) was studied by means of high-temperature x-ray diffractometry. Solidus and occasional liquidus temperatures were approximated, so that tentative partial phase diagrams for 33 oxide additions were constructed. Only the monoclinic and the cubic forms of Bi(2)O3 were found to be stable. Other phases, frequently reported by previous investigators, such as tetragonal and body-centered cubic (b.c.c.), were shown to form metastably from cooled liquid or cubic. An impure b.c.c. phase of distinct but variable composition appeared in systems of ZnO, PbO, B(2)O(3), Al(2)O(3), Ga(2)O(3), Fe(2)O(3), SiO(2), GeO(2), TiO(2), and P(2)O(5). The impure b.c.c. phase in the systems with SiO(2), GeO(2), and TiO(2) melted congruently about 100 °C above the m.p. of Bi(2)O(3). The impure b.c.c. phase was formed metastably in systems with Rb(2)O, NiO, MnO, CdO, V(2)O(5), and Nb(2)O(5); the conditions of formation were dependent on composition, preparation, and heating schedules. The impure b.c.c. phases, both stable and metastable, had smaller unit cell dimensions than that of pure Bi(2)O(3).