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

Abstract

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.

Authors:
 [1];  [1]
  1. Ames Laboratory
Publication Date:
Research Org.:
Ames Lab., Ames, IA (United States)
Sponsoring Org.:
USDOE Office of Science (SC)
OSTI Identifier:
1159303
Report Number(s):
IS-j 8393
Journal ID: ISSN 1098-0121; PRBMDO; ArticleNumber: 235126
DOE Contract Number:  
DE-AC02-07CH11358
Resource Type:
Journal Article
Journal Name:
Physical Review. B, Condensed Matter and Materials Physics
Additional Journal Information:
Journal Volume: 89; Journal Issue: 23; Journal ID: ISSN 1098-0121
Publisher:
American Physical Society (APS)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE

Citation Formats

Alam, Aftab, and Johnson, Duane D. Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study. United States: N. p., 2014. Web. doi:10.1103/PhysRevB.89.235126.
Alam, Aftab, & Johnson, Duane D. Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study. United States. https://doi.org/10.1103/PhysRevB.89.235126
Alam, Aftab, and Johnson, Duane D. 2014. "Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study". United States. https://doi.org/10.1103/PhysRevB.89.235126.
@article{osti_1159303,
title = {Mixed valency and site-preference chemistry for cerium and its compounds: A predictive density-functional theory study},
author = {Alam, Aftab and Johnson, Duane D.},
abstractNote = {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.},
doi = {10.1103/PhysRevB.89.235126},
url = {https://www.osti.gov/biblio/1159303}, journal = {Physical Review. B, Condensed Matter and Materials Physics},
issn = {1098-0121},
number = 23,
volume = 89,
place = {United States},
year = {Sun Jun 01 00:00:00 EDT 2014},
month = {Sun Jun 01 00:00:00 EDT 2014}
}