On polymorphism and morphotropism of rare earth sesquioxides

The data on the phase transitions in the series of rare earth sesquioxides are considered in terms of the thermodynamic theory of morphotropism. It is shown that the scheme of polymorphism and morphotropism suggested by V.V. Glushkova is the most adequate. The derivatographic dehydration of lanthanum and neodymium oxide hydrates is performed. The transition of the cubic C modification into the hexagonal A modification of neodymium oxide is accompanied by the removal of volatile impurities and, thus, is not a polymorphic transition proper. (C) 2002 MAIK Nauka/Interperiodica.