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Microstrain‐assisted polymorphic phase transitions in (Eu 1− x La x ) 2 O 3
Author(s) -
Irshad K. A.,
Saikumaran A.,
Srihari V.,
Kalavathi S.,
Chandra Shekar N. V.
Publication year - 2019
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576718016989
Subject(s) - monoclinic crystal system , crystallography , crystal structure , materials science , rietveld refinement , phase transition , phase (matter) , powder diffraction , x ray crystallography , diffraction , ionic radius , chemistry , physics , ion , condensed matter physics , optics , organic chemistry
Solid solutions, (Eu 1− x La x ) 2 O 3 (0 ≤ x ≤ 1), of the rare earth sesquioxides Eu 2 O 3 and La 2 O 3 have been prepared by a simple soft chemistry approach. The composition and morphology of the as‐synthesized oxides have been characterized using energy‐dispersive spectroscopy and scanning electron microscopy. The particles are of irregular shape and submicrometre size. In order to understand the structural evolution as a function of composition, angle‐dispersive X‐ray diffraction measurements have been carried out and the structural parameters have been obtained through Rietveld refinement. A structural phase transition from the cubic ( C ‐type) to the monoclinic ( B ‐type) structure and subsequently to the hexagonal ( A ‐type) structure was observed with an increasing substitution of La. A detailed analysis of the transition boundaries in terms of the average cationic radius, R RE , shows that the onset of the C → B transition is at R RE = 0.980 Å, whereas the B → A transition occurs at R RE = 1.025 Å. A biphasic region of cubic and monoclinic structures is observed for 0.2 ≤ x ≤ 0.4 and one of monoclinic and hexagonal structures is observed for 0.5 ≤ x ≤ 0.6. The microstrain induced by the difference in size of the rare earth cations introduces a substitutional disorder in the crystal structure, which is a plausible cause of the observed phase transitions in these oxides.