Abstract
Lanthanide(Ln) oxides represent an array of materials which exhibit unique properties, such as, superior mechanical, thermal, optical and magnetic properties, derived by their unfilled semicore 4f orbitals. Two forms of cerium oxide(CeO2 and Ce2O3) for instance have been the subject of numerous studies aiming to elucidate chemical and physical characteristics of their bulk and thin film properties. Cerium oxides have been widely deployed as catalysts in the preparation of active metal nanoparticles, as electrolytes or anode support materials. On the theoretical side, density functional theory(DFT) investigation has elucidated structures and electronic properties by utilizing hybrid DFT methods. Studied compounds include the A-type hexagonal structure and CeO2 with the cubic fluorite structure (space group Fm-3m). This study presents a comprehensive DFT + U account into electronic structures, mechanical properties of C-type lanthanide sesquioxides and thermodynamic (redox) properties. The aim of this work is fourfold: (1) to evaluate the effects of the Hubbard U parameter on the electronic and structural properties of C-type lanthanide sesquioxides (Ln2O3), (2) to assess the mechanical stability of all C-type lanthanide sesquioxides, (3) to elucidate the thermodynamic feasibility of CeO2 to undergo a redox reaction at temperatures relevant to catalytic applications, and (4) to underpin the effect of adding Hf and Zr to CeOδ [ δ=2-1.5] on reduction energies. We find that a Ueff value of ~ 5 eV reproduces the analogous experimental band gap of Ce2O3. Bader’s charge distributions on the C-type Ln2O3 have verified the ionic bonding nature of these compounds. Our analysis for the reduction energy of CeO2, in a wide range of temperatures, demonstrates that transfer cerium oxide between the two + 4 and + 3 oxidation states exhibit a temperature independent behavior. Preliminary results indicate that CeO2 alloyed with Hf or Zr results in enhancing its redox characteristics by lowering reduction enthalpies.