Coexistence of several sillenite-like phases in pseudo-binary and pseudo-ternary systems based on Bi_2O_3

摘要

A series of polycrystalline samples containing sillenite-like (doped γ-M_2O_3) phases were prepared by high-temperature reactions from (α-Bi_2O_3 powder and different oxides in six pseudo-binary Bi_2O_3-M_xO_y (M = Mn, Ti, V) and six pseudo-ternary Bi_2O_3-M1_xO_y,-M2_xO_y (Ml = Pb, Zn, Ti and M2 = Zn, Ti, Si) systems. The products were characterized by XRD, SEM/EDX, HRTEM, SAED and DTA techniques. It is shown that for pseudo-binary systems, the phase composition of specimens depends on dopant content, while, for pseudo-ternary systems, depends on dopants radii, as well. In pseudo-binary systems, single-phase sillenites are obtained if the dopant content is in accordance with formula Bi_(12)M~(4+)O_(20), for M = Mn and Ti, and Bi_(12)(M_(0.8)~(5+))O_(20), for M = V. However, two coexisting sillenite-like phases, doped compound and nominally undoped solid solution, are found if a half of that dopant quantity is applied. In pseudo-ternary systems, the phase-pure double-doped sillenite specimens are identified if ionic radii of dopants differ less than 40%. Otherwise, two coexisting sillenites were obtained. The possibility to prepare the undoped γ-Bi_2O_3 phase was also discussed.