Abstract
Using the density functional theory, we study the structural and lattice dynamical properties of europium sesquioxide (Eu2O3) in the cubic, trigonal, and monoclinic phases. The obtained lattice parameters and energies of the Raman modes show a good agreement with the available experimental data. The Eu-partial phonon density of states calculated for the cubic structure is compared with the nuclear inelastic scattering data obtained from a 20 nm thick Eu2O3 film deposited on a YSZ substrate. A small shift of the experimental spectrum to higher energies results from a compressive strain induced by the substrate. On the basis of lattice and phonon properties, we analyze the mechanisms of structural transitions between different phases of Eu2O3.
Highlights
Due to the high reactivity with oxygen, the most stable compounds of rare-earth (RE) elements are their oxides with a general formula R2O3, called sesquioxides, in which the RE ions (R) exist in the trivalent state.[1]
A direct phase transition from the C-type structure to the B-type monoclinic structure was observed at about 8.0 GPa, and the B-type structure was retained after the pressure was released, indicating that the monoclinic phase is metastable at room temperature.[6]
In order to verify the ab initio calculations performed for the cubic phase, the theoretical results were compared with the Eu-partial phonon density of states (DOS) of a polycrystalline Eu2O3 film obtained from nuclear inelastic scattering (NIS)
Summary
Due to the high reactivity with oxygen, the most stable compounds of rare-earth (RE) elements are their oxides with a general formula R2O3, called sesquioxides, in which the RE ions (R) exist in the trivalent state.[1]. Eu2O3 crystallizes in a cubic (C) structure and experiences structural transformations to monoclinic (B), trigonal (A), hexagonal (H), and cubic (X) phases with increasing temperature.[1,4] Under pressure, the structural transition from the cubic C-type to the trigonal Atype phase, which starts at 5.0 GPa and finishes at about 13.1 GPa, is observed. This transition leads to a volume collapse of 9% at 8.6 GPa.[5] The trigonal phase remains stable up to the highest experimentally feasible pressure. At ambient conditions, Eu2O3 may exist in a stable cubic form and in a metastable B-
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