Phase equilibria in systems involving the rare-earth oxides. Part I. Polymorphism of the oxides of the trivalent rare-earth ions | Zendy

R. S. Roth | Zendy; Samuel J Schneider | Zendy

Open Access

Phase 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.

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