Progressive reduction from CeO2 to Ce2O3

R. OLBRICH; G. E. MURGIDA; V. FERRARI; C. BARTH; A. M. LLOIS; M. REICHLING; M. V. GANDUGLIA PIROVANO

Congreso; DPG Spring Meeting of the Condensed Matter Section (SKM) together with the EPS; 2018

The progressive reduction from CeO2 to Ce2O3 of a 180nm thick ceriafilm annealed in an ultra-high vacuum (UHV) environment at temperaturesup to 1100K is observed by direct imaging with a non-contactatomic force microscope (NC-AFM). By combining high-resolutionNC-AFM imaging with spin-polarized DFT+U calculations, we identifyfour surface reconstructions namely?ã︀(7)?~?ã︀(7)R19.1∘ Ce7O12,(7) ?~ 3R19.1∘ Ce3O5,?ã︀(3)?~?ã︀(3)R30∘ Ce3O5 and 1 ?~ 1 Ce2O3.We combine DFT total energy calculations with statistical thermodynamicsto explain the sequence of occurrence of the observed phasesand their coexisting at evaluated temperatures. The ?ã︀(7)?~3 phase isthe only phase that has an unexpected oblique rather than a hexagonalstructure. This phase only exists as a thin reduced over layer and cannot be prepared in the bulk.