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

作者：Alam Aftab^*; Johnson D D

来源：Physical Review B, 2014, 89(23): 235126.

DOI：10.1103/PhysRevB.89.235126

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)(14)B permanent magnets, we find a stable mixed-valent alpha state near the spectroscopic value of nu(s) = 3.53. Ce valency in compounds depends on its steric volume and local chemistry. For La doping, Ce valency shifts towards gamma-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.

• 出版日期2014-6-23