Solid solutions, (Eu 1Àx 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, angledispersive 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.

No abstract

No abstract

No abstract