ON RARE EARTH DIOXYMONOCARBONATES AND THEIR DECOMPOSITION

The polymorphic forms of Ln2O2CO3 have been prepared and further characterized by high-temperature X-ray diffraction, tensimetric, and infrared methods. The X-ray study reveals a regular variation with atomic number for cell parameters and decomposition temperatures. The intermediate Ln2O3.yCO2 reported by others is shown to be a mixture of Ln2O2CO3 (II) + Ln2O3. The crystal structures for the polymorphic forms (type I, tetragonal; type IA, monoclinic; type II, hexagonal) are further elucidated by thermal expansion measurements and by the infrared data. In particular, the orientation of carbonate groups in the three structures is correlated to the resulting vibrational modes in the region 600-1800 cm-1. © 1969, American Chemical Society. All rights reserved.