Open AccessPhase equilibria in systems involving the rare-earth oxides. Part I. Polymorphism of the oxides of the trivalent rare-earth ions
Author(s) -
R. S. Roth,
Samuel J Schneider
Publication year - 1960
Publication title -
journal of research of the national bureau of standards. section a. physics and chemistry
Language(s) - English
Resource type - Journals
eISSN - 2376-5704
pISSN - 0022-4332
DOI - 10.6028/jres.064a.030
Subject(s) - rare earth , metastability , polymorphism (computer science) , ion , oxide , crystallography , phase (matter) , structural type , materials science , chemistry , solid solution , ionic radius , inorganic chemistry , mineralogy , metallurgy , organic chemistry , biochemistry , genotype , gene
The polymorphic relationships of the pure rare-earth oxides have been reinvestigated using X-ray diffraction methods for identification of phases. The oxides of the trivalent rare earth ions crystallize in three different types: A, B, and C. Each oxide has only one truly stable polymorph: La 2 O 3 , Ce 2 O 3 , Pr 2 O 3 , and Nd 2 O 3 belong to the A type; Sm 2 O 3 , Eu 2 O 3 , and Gd 2 O 3 to the B type; Tb 2 O 3 , Dy 2 O 3 , Ho 2 O 3 , Er 2 O 3 , Tm 2 O 3 , Yb 2 O 3 , and Lu 2 O 3 to the C type. In addition Nd 2 O 3 , Sm 2 O 3 , Eu 2 O 3 , and Gd 2 O 3 have low-temperature, apparently metastable, C-type polymorphs. The low-temperature form inverts irreversibly to the stable form at increasingly higher temperatures for decreasing cation radius.