The binary system Bi2O3-La2O3 with La2O3 greater than or equal to 50 m
ole% has been investigated at 950-1000 degrees C, The results revealed
three compounds: Bi8La10O27, Bi2.4La3.6O9, and Bi2La4O9. Bi2.4La3.6O9
has a rhombohedral subcell with hexagonal lattice parameters a = 3.96
017(5) Angstrom, c = 9.9691(2) Angstrom, and space group R3m. It is pr
obably the same phase which was reported previously as Bi2La4O9 (Refs.
5 and 6). Bi2La4O9 has a monoclinic structure with the subcell lattic
e parameters a = 6.8290(3) Angstrom, b = 3.9887(1) Angstrom, c = 4.052
4(1) Angstrom and beta = 125.094(3)degrees and subcell space group C2/
m. Its average structure has been determined by X-ray powder diffracti
on and refined by the Rietveld method. The average structure can be de
scribed as an oxygen deficient fluorite structure of the delta-Bi2O3 t
ype with La and Bi randomly distributed on the cation site. In additio
n, a superstructure has been observed by TEM. (C) 1996 Academic Press,
Inc.