A systematic study of the oxygen K edge in the cubic and less common monoclinic phases ofthe rare earth oxides (Ho, Er, Tm, Yb) by electron energy loss spectroscopy

Abstract

Transmission electron microscopy and electron energy loss spectroscopy (EELS) were usedto distinguish structural details for the cubic and uncommon monoclinic crystal phases ofheavy metal rare earth oxide nanoparticles synthesized by a combustion process.Specifically, we systematically examined the EELS oxygen K edge for Ho, Tm, Er, andYb sesquioxides in both phases. This work presents, to our knowledge, the firstEELS study of the monoclinic phase in these materials and the first systematiccomparative study between the monoclinic and cubic phases across a range of rare earthsesquioxides. For both phases, we observed the usual double-peak structure ofthe oxygen K edge typically seen for oxygen atoms tetrahedrally surrounded bymetal atoms, but we found the details of the energy loss near-edge structure todiffer substantially between the two phases. Our results indicate a greater peakseparation for the cubic than for the monoclinic phase. Furthermore, a trend ofincreasing peak separation with increasing atomic number was also noted for bothphases in the series of rare earth oxide nanoparticles. Our results show that thefine structure in EELS can be utilized to determine differences on the nanoscalebetween the common cubic structure and the less common monoclinic structure.