Roth R S, Schneider S J
J Res Natl Bur Stand A Phys Chem. 1960 Jul-Aug;64A(4):309-316. doi: 10.6028/jres.064A.030. Epub 1960 Aug 1.
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: LaO, CeO, PrO, and NdO belong to the A type; SmO, EuO, and GdO to the B type; TbO, DyO, HoO, ErO, TmO, YbO, and LuO to the C type. In addition NdO, SmO, EuO, and GdO 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.
利用X射线衍射方法对纯稀土氧化物的多晶型关系进行了重新研究，以鉴定物相。三价稀土离子的氧化物以三种不同类型结晶：A、B和C型。每种氧化物只有一种真正稳定的多晶型：LaO、CeO、PrO和NdO属于A型；SmO、EuO和GdO属于B型；TbO、DyO、HoO、ErO、TmO、YbO和LuO属于C型。此外，NdO、SmO、EuO和GdO具有低温、明显亚稳的C型多晶型。随着阳离子半径减小，低温形式在越来越高的温度下不可逆地转变为稳定形式。
