Size and spatial correlation of defective domains in yttrium-doped CeO₂

Abstract

The size of dopant-rich nanodomains was assessed in four samples of Ce 1−μ Y μ O 2−μ/2 through systematic pair distribution function (PDF) refinements. Experimental G(r) curves were fitted by different structural models with the aim of finding a description which balanced precise structure parameterization and reasonable number of parameters. The most reliable model was a single Y 2 O 3 -like phase, which best accommodated to the close relationship between the fluorite (CeO 2 -like) and C-type (Y 2 O 3 -like) structures. In this model, a refined cation coordinate, x(M2), measured the relative occurrence in the G(r) of the chemical environment of Y and Ce at any value of r. The r-value at which x(M2) vanished, i.e. at which the refined C-type cell becomes a redundant, low-symmetry description of a fluorite cell, was assumed as the size of a C-type domain. Subtle features in G(r) could be attributed to the fluorite or C-type phase up to~500 Å thanks to the narrow instrumental resolution function of the ID31 beamline (now ID22) at the ESRF, which allows us to get high resolution PDF data.

Phase Transformations in the CeO2–Sm2O3 System: A Multiscale Powder Diffraction Investigation

“…It can be pictured as the formation of Ctype distorted regions rich in dopant and oxygen vacancies, defined as droplets, embedded in a fluorite matrix, as already observed for other dopants [28,29]. The C-type phase fractions returned by the fit are given in Table 3 The extent of the domains rich in oxygen vacancies was estimated by monitoring the r-distance dependence of x(M2) using the strategy described in [48]. Since a single C-type phase is considered for this purpose, x(M2) is averaged over fluorite (x(M2)=0) and C-type (x(M2)<0) regions, therefore it is less negative than for the biphasic model.…”

Rare Earth Doped Ceria: The Complex Connection Between Structure and Properties

“…In this model, C-type domains are embedded in a fluorite matrix and their size increases with x until complete transformation to C-type. Details on the data analysis strategy were reported in Checchia et al ( 2015 ). C-type domains as large as 12 nm were observed already for x = 0.25, when the structure is fluorite.…”

Precise implications for real-space pair distribution function modeling of effects intrinsic to modern time-of-flight neutron diffractometers

“…Total scattering and pair distribution function (PDF) analysis methods have been evolving rapidly in recent years (Farrow et al, 2007;Billinge & Levin, 2007;Playford et al, 2014;Egami & Billinge, 2012;Keen & Goodwin, 2015;Mancini & Malavasi, 2015) as the advent of faster computers has allowed for increasingly complex modeling programs such as RMCProfile (Tucker et al, 2007), DEBUSSY (Cervellino et al, 2015) and FullRMC (Aoun, 2016), to address longer length-scale correlations. At the same time, the complexity of many modern material studies often involves characterizing the structural correlations and nanoscale ordering at length scales on the order of tens to hundreds of å ngströ ms (Aksel et al, 2013;Coduri et al, 2013;Hill & Allieta, 2013;Usher et al, 2015;Allieta et al, 2015;Checchia et al, 2015;Liu et al, 2016Liu et al, , 2017Jiang et al, 2017). To take full advantage of the higher-fidelity models, the need to measure reliable, long length-scale spanning, high-resolution PDFs is greater than ever.…”