Preparation of a new triclinic phase based on a pseudo-fcc subcell in the systems Bi2O3-Ln(2)O(3) (Ln=Dy,Ho,Er, and Y)

A phase equilibrium study of the systems Bi2O3-Ln(2)O(3) (Ln = lanthanoid including Y) has found a new Bi(1-x)Ln(x)O(1.5) (Ln = Dy, Ho, Er, and Y with x = 0.485, 0.485-0.49, 0.49, and 0.475-0.49, respectively). A repetitive long-term solid-state reaction at about 800 degrees C has generated this low-temperature stable phase. It crystallizes ia the triclinic system with a similar or equal to 8.5 Angstrom, b similar or equal to 10 Angstrom, c similar or equal to 8.5 Angstrom, alpha similar or equal to 111 degrees, beta similar or equal to 106 degrees, gamma similar or equal to 94 degrees, and Z = 16. This triclinic structure is based on a pseudo-fee subcell with a' similar or equal to 5.4 Angstrom. The axial relations between the triclinic supercell and the subcell are a similar or equal to root 5/2a', b similar or equal to root 7/2a', and c similar or equal to root 5/2a'. When heated, the triclinic phase transforms smoothly into the delta-Bi2O3 type high-temperature stable phase around 1000 degrees C; when it is cooled, its rate of transition in the opposite direction is extremely sluggish. This sluggishness seems to be due to the ordering of the cations, Bi3+ and Ln(3+), in the triclinic structure. (C) 1996 Academic Press, Inc.