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

Abstract

The need for high efficiency energy production, conversion, storage and transport is serving as a robust guide for the development of new materials. Materials with physical-chemical properties matching specific functions in devices are produced by suitably tuning the crystallographic- defect- and micro-structure of the involved phases. In this review, we discuss the case of Rare Earth doped Ceria. Due to their high oxygen diffusion coefficient at temperatures higher than ~500°C, they are very promising materials for several applications such as electrolytes for Solid Oxide Fuel and Electrolytic Cells (SOFC and SOEC, respectively). Defects are integral part of the conduction process, hence of the final application. As the fluorite structure of ceria is capable of accommodating a high concentration of lattice defects, the characterization and comprehension of such complex and highly defective materials involve expertise spanning from computational chemistry, physical chemistry, catalysis, electrochemistry, microscopy, spectroscopy, and crystallography. Results coming from different experimental and computational techniques will be reviewed, showing that structure determination (at different scale length) plays a pivotal role bridging theoretical calculation and physical properties of these complex materials.

In Situ High Pressure Structural Investigation of Sm-Doped Ceria

“…This correlation assumes different forms for ionic crystals and oxides. In particular, the expression ln = ln 2 ln (5) with and as the cationic and anionic charge, respectively, applies to ionic crystals, while ln = ln 2 (6) with ranging between 3 and 4, is valid for oxides. A decreasing linear trend is observed in both cases, which accounts for the progressively increasing compressibility of a solid with an increasing…”

“…However, even a slight variation in RE content causes a non-negligible change in ionic conductivity; Ce 0.8 Gd 0.2 O 1.90 , for example, is characterized by a total ionic conductivity of 1 × 10 −3 S cm −1 at 773 K [2]. Ionic conductivity is in fact affected by many factors such as RE identity, composition, structure and microstructure of the oxide [3][4][5][6][7], and not least by the occurrence of the sample in the bulk or thin film form. With particular reference to this latter issue, thin films are essential when designing SOFC-based portable devices because of the need for fabricating fuel cells on chips [8,9].…”

“…Scheme of the experimental set-up at the XPRESS beamline. (1) Pair of identical diamonds;(2) metal foil with a hole at the center (sample chamber); (3) sample chamber (sample, ruby, pressure transmitting medium (PTM)); (4) backing plates holding diamonds; (5) force pushing diamonds;(6) laser for ruby fluorescence excitation;(7) incident monochromatic x-ray microbeam; (8) diffracted xrays; (9) beam stop blocking the direct beam; (10) image plate detector recording the position and intensity of the diffracted x-rays.…”

High‐Temperature CO2 Electrolysis in Solid Oxide Electrolysis Cells: Developments, Challenges, and Prospects

“…Similar with zirconia, the conductivity of ceria can be remarkably improved by doping divalent or trivalent cations into Ce site . The doped ceria, such as GDC (Gd 2 O 3 ‐doped ceria) or SDC (Sm 2 O 3 ‐doped ceria), exhibits higher conductivity than YSZ.…”

Local and Average Structure of Yb-Doped Ceria through Synchrotron and Neutron Pair Distribution Function

“…Keeping in mind that reported solubilities are affected by the synthesis route, La doping can reach µ = 50%, maintaining long-range fluorite [19,20], while Yb is reported to enter fluorite up to µ = 40% [21]. However, it should be noted that slight C-type distortions from fluorite give rise to tiny superstructure peaks that can be easily missed unless recurring to synchrotron radiation (see [3] and references therein). Structural details about fluorite and C-type structures are discussed elsewhere [22] and will be recalled later.…”