Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study

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Physical Review B, ISSN: 1098-0121, Vol: 89, Issue: 23, Page: 235126

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https://lib.dr.iastate.edu/ameslab_pubs/271; https://works.bepress.com/duane_johnson/21
Alam, Aftab; Johnson, Duane D.
American Physical Society (APS)
Materials Science; Physics and Astronomy; Materials Science and Engineering
article description
Cerium and its technologically relevant compounds are examples of anomalous mixed valency, originating from two competing oxidation states - itinerant Ce4+ and localized Ce3+. Under applied stress, anomalous transitions are observed but not well understood. Here we treat mixed valency as an "alloy" problem involving two valences with competing and numerous site-occupancy configurations. We use density-functional theory with Hubbard U (i.e., DFT+U) to evaluate the effective valence and predict properties, including controlling the valence by pseudoternary alloying. For Ce and its compounds, such as (Ce,La)2(Fe,Co)14B permanent magnets, we find a stable mixed-valent α state near the spectroscopic value of νs=3.53. Ce valency in compounds depends on its steric volume and local chemistry. For La doping, Ce valency shifts towards γ-like Ce3+, as expected from steric volume; for Co doping, valency depends on local Ce-site chemistry and steric volume. Our approach captures the key origins of anomalous valency and site-preference chemistry in complex compounds. © 2014 American Physical Society.