Hypothetical CeO2—Ln2O3 phase diagrams (Ln = yttrium lanthanides, Y2O3)

Based on the analysis of literature data from the experimentally constructed phase diagrams of CeO2—Ln2O3 systems (Ln = Tb—Lu), as well as the temperatures of polymorphic transformations of oxides of rare earth elements (REEs), approximate phase diagrams of the indicated system were constructed in the entire range of temperatures and concentrations. Cerium dioxide crystallizes in the cubic type of fluorite crystal lattice and has no polymorphic transformations in the entire temperature range until melting at 2400 ºC. The solubility based on CeO2 is higher than based on other lanthanide oxides. The components of the systems show complete solubility below solidus with the formation of solid solutions with a structure of the fluorite-type F. The appearance below the solidus regions of solid solutions based on polymorphic modifications of lanthanide oxides H, A, B and C with different width leads to the formation of cascades of peritectoid transformations. During the transition in the Tb—Lu series, their temperatures gradually increase, which is associated with an increase in the temperatures of polymorphic transformations of Tb—Lu oxides. Hypothetical phase diagrams of the CeO2—Ln2O3 series (Ln = Tb—Lu, Y) with adjustments according to such regularities of interaction during the transition from Tb to Lu. Experimental verification of the phase diagrams structure of the considered systems is possible when conducting experiments using increased pressures of oxygen-containing media, or by thermodynamic calculations. Keywords: REE oxides, Y2O3, CeO2, polymorphic transformation of REE, phase diagrams.