PREDICTION OF NOVEL BAMNO3-Y (0-LESS-THAN-Y-LESS-THAN-0.1) PEROVSKITE RELATED PHASES

An electron diffraction and microscopy study of the BaMnO3-y system indicates that for 0.1 < y < 0.25 several types crystallize showing hexagonal symmetry, rhombohedral types being obtained for 0 < y < 0.1. On the basis that oxygen deficiency is accommodated by the introduction of BaO2.5 cubic layers in the hexagonal close packing of BaMnO3, the existence of different types can be predicted, taking into account that the anionic composition can be deduced from the expression y = 0.5c/(c + h), where c and h refers to the number of cubic and hexagonal layers per unit cell, respectively. Electron microscopy proves the existence of new rhombohedral types (21R, 27R, 33R) along the 0 < y < 0.1 range. (C) 1994 Academic Press, Inc.