Evaluation of the Defect Cluster Content in Singly and Doubly Doped Ceria through In Situ High-Pressure X-ray Diffraction

Abstract

Defect aggregates in doped ceria play a crucial role in blocking the movement of oxygen vacancies and hence in reducing ionic conductivity. Nevertheless, evaluation of their amount and the correlation between domain size and transport properties is still an open issue. Data derived from a high-pressure X-ray diffraction investigation performed on the Ce 1– x (Nd 0.74 Tm 0.26 ) x O 2– x /2 system are employed to develop a novel approach aimed at evaluating the defect aggregate content; the results are critically discussed in comparison to the ones previously obtained from Sm- and Lu-doped ceria. Defect clusters are present even at the lowest considered x value, and their content increases with increasing x and decreasing rare earth ion (RE 3+ ) size; their amount, distribution, and spatial correlation can be interpreted as a complex interplay between the defects’ binding energy, nucleation rate, and growth rate. The synoptic analysis of data derived from all of the considered systems also suggests that the detection limit of the defects by X-ray diffraction is correlated to the defect size rather than to their amount, and that the vacancies’ flow through the lattice is hindered by defects irrespective of their size and association degree.

High Pressure X-ray Diffraction as a Tool for Designing Doped Ceria Thin Films Electrolytes

“…The authors' research group focused on RE-doped ceria systems containing RE ≡ Lu [11], Sm [12] and a mixture of Nd/Tm ions [13]. In particular, the last-mentioned system was synthesized using a Nd/Tm = 0.74/0.26 ratio, in order to reproduce the average ionic size of Sm 3+ (C.N.…”

“…All the samples were prepared by coprecipitation of the corresponding mixed oxalates, and by subsequent thermal treatment at 1173 K for 3 days in order to obtain a high crystallinity degree, as thoroughly described in [41,76]. Going into detail, authors studied Ce 1−x RE x O 2−x/2 systems with x ranging between 0.1 and 0.4 for RE ≡ Lu [11], 0.2 and 0.6 for RE ≡ Sm [12], and 0.1 and 0.6 RE ≡ (Nd,Tm) [13]. Moreover, regarding the Lu-doped ceria system, even the composition having x = 0.8 was studied.…”

“…X-ray diffraction is well known to be a powerful experimental technique, which provides a fundamental contribution to the comprehension of structure [41], microstructure [72], occurrence of defects [13], and crystallinity [73]. In the particular case of doped ceria, it is evident that strain contributes in a fundamental way to ionic conduction of thin films.…”

“…Trend of lnB 0 vs. ln(2V at ) for all the studied systems. Data of CeO 2 are taken from [88], while the ones of the Sm-and (Nd,Tm)-containing systems derive from [13]; experimental points of Lu-doped ceria are taken from [12]. Cell volumes of samples crystallizing in the F phase are multiplied by 8 in order to make them comparable with those crystallizing in the C structure.…”

“…An effective approach aimed at avoiding the experimental difficulties associated to the study of interfaces consists in the investigation of the high pressure behaviour of bulk samples to simulate the interfacial strain [10] and deduce the material compressibility. Following this idea, recently, several high pressure X-ray diffraction studies were performed by this [11][12][13] and other research groups [10] with the aim to determine the bulk modulus of several samples belonging to different RE-doped ceria systems, and finally to gain useful hints for the selection of the most proper compositions in the design of thin films.…”