A new hierarchical approach is presented for elucidating the structural disorder in Ce1-xGdxO2-x/2 solid solutions on different scale lengths. The primary goal of this investigation is to shed light on the relations between the short-range and the average structure of these materials via an analysis of disorder on the mesocopic scale. Real-space (pair distribution function) and reciprocal-space (Rietveld refinement and microstructure probing) analysis of X-ray powder diffraction data and electron spin resonance (ESR) investigations were carried out following this approach. On the local scale, Gd- and Ce-rich droplets (i.e. small regions a few a°ngstro¨ms wide) form, exhibiting either a distorted fluorite (CeO2) or a C-type (Gd2O3) structure in the whole compositional range. These droplets can then form C-type nanodomains which, for Gd concentrations xGd > 0.25, are embedded in the fluorite matrix. At the site percolation threshold pC for a cubic lattice (xGd = pC ’ 0.311), C-type nanodomains percolate inside each crystallite and a structural phase transformation is observed. When this occurs, the peak-to-peak ESR line width DHpp shows a step-like behaviour, which can be associated with the increase in Gd–Gd dipolar interactions. A general crystallographic rationale is presented to explain the fluorite-to-C-type phase transformation. The approach shown here could be adopted more generally in the analysis of disorder in other highly doped materials.
Percolating hierarchical defect structures drive phase transformation in Ce1-xGdxO2-x/2 : a total scattering study / M. Scavini, M. Coduri, M. Allieta, P. Masala, S. Cappelli, C. Oliva, M. Brunelli, F. Orsini, C. Ferrero. - In: IUCRJ. - ISSN 2052-2525. - 2(2015), pp. 511-522.
|Titolo:||Percolating hierarchical defect structures drive phase transformation in Ce1-xGdxO2-x/2 : a total scattering study|
|Parole Chiave:||doped ceria; disorder; pair distribution function; high-resolution X-ray powder diffraction; percolation; hierarchy; solid eectrolytes; electron spin resonance|
|Settore Scientifico Disciplinare:||Settore CHIM/02 - Chimica Fisica|
|Data di pubblicazione:||2015|
|Data ahead of print / Data di stampa:||2015|
|Digital Object Identifier (DOI):||http://dx.doi.org/10.1107/S2052252515011641|
|Appare nelle tipologie:||01 - Articolo su periodico|