Charge localization increases chemical expansion in cerium-based oxides

Abstract

In this work, we demonstrate the mechanism by which electronic charge localization increases the chemical expansion coefficient in two model systems, CeO 2Àd and BaCeO 3Àd . Using Density Functional Theory calculations, we predict that this coefficient is increased by more than 70% when charge is fully localized, consistent with the observation that materials with a smaller degree of charge localization have smaller chemical expansion coefficients. This finding has important consequences for devising materials with smaller chemical expansion coefficients and for the reliability of the widely-used Shannon's ionic radii.

Reducing the chemical expansion coefficient in ceria by addition of zirconia

“…The importance of charge localization was also recognized in a subsequent study. 17 An interesting result of our investigation was that the contraction due to the formation of an oxygen vacancy in ZrO 2 (upon acceptor doping) is 91% larger than in CeO 2 , leading to our prediction that a CeO 2 -ZrO 2 solid solution will have a smaller chemical expansion coefficient. 16 In this communication, we test this hypothesis, both experimentally and computationally, and show that the solid solution indeed exhibits a signicant ($50%) decrease in a C .…”

Strain-controlled oxygen vacancy formation and ordering in CaMnO3

“…This phenomenon, known as chemical expansion, is most pronounced for perovskites containing transition metal ions that can adopt a variety of valence states and hence can readily accommodate the associated change in formal charge 9 . Prominent examples are acceptor doped LaMnO 3 and donor doped SrTiO 3 10,11 , where significant volume expansions are observed as a function of the oxygen partial pressure.…”

Chemomechanics of ionically conductive ceramics for electrical energy conversion and storage

“…Marrocchelli et al suggested that zero chemical expansion in a material could be obtained by choosing material compositions that balance these two effects. In later, related work, Marrocchelli et al determined that charge localization at the cation increased chemical expansion relative to a structure with distributed charge [92]. With localized charge, the change in the radius of ceria upon reduction would be greater than if the charge were delocalized, causing an increase in chemical expansion for structures with higher degrees of charge localization.…”

“…Marrocchelli et al used DFT + U (indicating inclusion of a Hubbard term) to calculate the effect of charge delocalization on the chemical expansion coefficient of CeO 2−δ and BaCeO 3−δ [92]. In that study, varying the U term changed the extent of localization of 4f electrons at the ceria cation.…”

“…Density functional theory (DFT) is a type of atomistic modeling that can be used to investigate the electronic structure of materials and a wide range of related properties, such as the elastic constants [89], the energy barrier to vacancy migration [90] and the diffusion coefficients of various point defects [91] or, in combination with molecular dynamics (MD) simulations, the chemical expansion behavior of a given material [92].…”