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LaNiO3 (LNO) is an intriguing member of the rare-earth nickelates in exhibiting a metal-insulator transition for a critical film thickness of about 4 unit cells [Son et al., Appl. Phys. Lett. 96, 062114 (2010)]; however, such thin films also show a transition to a metallic state in superlattices with SrTiO3 (STO) [Son et al., Appl. Phys. Lett. 97, 202109 (2010)]. In order to better understand this transition, we have studied a strained LNO/STO superlattice with 10 repeats of [4 unit-cell LNO/3 unit-cell STO] grown on an (LaAlO3)(0.3)(Sr2AlTaO6)(0.7) substrate using soft x-ray standing-wave-excited angle-resolved photoemission (SWARPES), together with soft- and hard- x-ray photoemission-measurements of core levels and densities-of-states valence spectra. The experimental results are compared with state-of-the-art density functional theory (DFT) calculations of band structures and densities of states. Using core-level rocking curves and x-ray optical modeling to assess the position of the standing wave, SWARPES measurements are carried out for various incidence angles and used to determine interface-specific changes in momentum-resolved electronic structure. We further show that the momentum-resolved behavior of the Ni 3d e(g) and t(2g) states near the Fermi level, as well as those at the bottom of the valence bands, is very similar to recently published SWARPES results for a related La0.7Sr0.3MnO3/SrTiO3 superlattice that was-studied using the same technique (Gray et al., Europhysics Letters 104, 17004 (2013)), which further validates this experimental approach and our conclusions. Our conclusions are also supported in several ways by comparison to DFT calculations for the parent materials and the superlattice, including layer-resolved density-of-states results.

© 2016 The American Ceramic Society. All rights reserved. We performed systematic ab initio atomistic simulations of monazite (LnPO4) and pyrochlore (A2B2O7 )-type ceramics. The simulated properties include the thermodynamic parameters, the threshold displacement energies, the elastic constants and the energies of defects formation. We computed the excess effects of mixing in various monazite-type solid solutions and provided crucial information on their thermodynamic stability. To better understand the radiation damage resistance of the considered novel waste forms, we simulated the threshold displacement energies and the displacement probabilities of La cation in LaPO4 monazite and computed defect formation energies in various pyrochlore compounds. The observed exothermic character of the anion Frenkel pair defects suggests that the ease of the defect formation correlates with instability of the pyrochlore structure relative to fluorite. Further calculations of activation barriers for the oxygen migration shed a light on the mechanism of the order-disorder transition in pyrochlore compounds.