First-Principles Investigation of Structural, Elastic and Electronic Properties of Lanthanide Titanate Oxides Ln 2 TiO 5
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First-Principles Investigation of Structural, Elastic and Electronic Properties of Lanthanide Titanate Oxides Ln2TiO5 Hui Niu,1 Huiyang Gou,1 Rodney C. Ewing2 and Jie Lian1 1
Department of Mechanical, Aerospace and Nuclear Engineering, Rensselaer Polytechnic Institute, Troy, NY 12180 2 Department of Geological Sciences, University of Michigan, Ann Arbor, MI 48105
ABSTRACT Systematic first-principles calculations based on density functional theory were performed on a wide range of Ln2TiO5 compositions (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Dy and Y) in order to understand the correlation between structural, elastic and electronic properties. A complete set of elastic parameters including elastic constants, Hill’s bulk moduli, shear moduli, Young’s moduli and Poisson’s ratio, were calculated. All Ln2TiO5 are ductile in nature, and analysis of densities of states and charge densities suggests that the oxide bonds are highly ionic. INTRODUCTION Lanthanide-doped titanate ceramics with compositions of Ln2TiO5 display high dielectrics and outstanding mechanical strength, thermal stability and chemical resistance and thus have important technological applications in nuclear enviornments. Specifically, Ln2TiO5 can be used as neutron absorbers in control rods for nuclear reactor operation due to their high thermal neutron absorption cross-sections of lanthanides (such as Eu, Dy and Gd).1-3 In addition, nano-sized yttrium titanate oxides of Y2TiO5 and Y2Ti2O7 have been identified as an important additive to strengthen oxide-dispersion strengthened (ODS), resulting in six orders of magnitudes increase in the creep resistance.4-5 These Y-Ti-O nanoclusters display great resistance toward radiation damage and thermal annealing, and the fundamental understanding of the energetics, electronic structure and the stabilizing mechanisms governing the phase stability will be critical for designing advanced structural materials for nuclear applications. Previous theoretical computations based on first-principles calculations reported that Y2TiO5 has lower elastic modulus of Y2TiO5 as compared with iron matrix, which may provide more effective dislocation pinning at high temperature through the mechanisms of activating barriers.6 In this work, we performed systematic first-principle calculations to investigate the structural, elastic and electronic properties of a wide range of rare-earth titanate oxides Ln2TiO5 (Ln =Y, La, Ce, Pr, Nd, Sm, Gd, Tb, and Dy) as a function of chemical compositions. Our results show that these oxides have high elastic modulus and toughness, and the electronic structure and nature of bond were analyzed. These results may provide theoretical knowledge which may be useful for designing advanced structural materials based on other rare-earth doped titanate oxides as strengthen additive in ODS alloys or as neutron absorbers in control rods for nuclear applications. COMPUTATION METHODOLOGY All calculations were performed within the framework of density function theory (DFT) using the Vienna ab initio simulation package
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