PREPARATION OF A NEW PHASE HAVING A CATION-ORDERED C-TYPE RARE-EARTH-OXIDE RELATED STRUCTURE IN THE SYSTEMS BI2O3-LN(2)O(3) (LN=SM,EU,GD,TB, AND DY)

A new phase Bi(1-x)Ln(x)O(1.5) has been found in the systems Bi2O3-Ln(2)O(3) (Ln = Sm, Eu, Gd, Tb, and Dy with x = 0.38, 0.375, 0.275-0.40, 0.275-0.35, and 0.30-0.35, respectively). The repetitive long-term solid-state reaction at about 800 degrees C has produced the present phase; this phase crystallizes in the cubic system I2(1)3 with a approximate to 11 Angstrom and Z = 32, has a structure closely related to the C-type rare-earth oxide one, and is the low-temperature stable phase. Upon heating, the present phase transforms smoothly into the delta-Bi2O3-type high-temperature stable phase around 900 degrees C. Upon cooling, however, a rate of transition of the opposite direction is extraordinarily sluggish. This sluggishness is discussed on the basis of the ordering of cations, Bi3+ and Ln(3+), in a proposed structure. (C) 1995 Academic Press, Inc