Thermodynamics of rare earth sesquioxides
Abstract
Experimental thermochemical and related data for rare earth sesquioxides, R2O3 (R = Sc, Y,
La–Lu) are critically reviewed to provide a consistent set of thermodynamic functions covering
the temperature range from at least 298 K up to above the melting point taking the polymorphism
into account. Discrepancies in the available data are discussed and further studies to resolve them
and to fill the gaps in the current knowledge are suggested. The best values for the temperatures
of the reversible polymorphic transformations are recommended. Using high-pressure and molar
volume data as well as ionic radius of a trivalent rare earth cation as an independent parameter
the relative stabilities of different structures (the cubic C-form, the monoclinic B-form, the hexagonal
A-form, the hexagonal H-form, and the cubic X-form) are estimated quantitatively for all rare earth
sesquioxides. Based on the empirical relationship between the entropy of fusion and the corresponding
fractional volume change, the entropies and enthalpies of fusion of the lanthanide sesquioxides
are estimated. The reliability of the assessed functions and transition data is tested through the
sample calculations of R'2O3–R''2O3 phase diagrams, where R' and R'' represent different rare earth
cations.
This item URI
http://hdl.handle.net/11256/965Collections
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