Processing, Phase Stability, and Conductivity of Multication-Doped Ceria

Abstract

Multicomponent doping of ceria with four cations is used as a preliminary investigation into the ionic conductivity of high-entropy-doped ceria systems. Different compositions of Ce1-x(Ndx/4Prx/4Smx/4Gdx/4)O2-δ (x = 0.05, 0.10, 0.15, and 0.20) are synthesized using the oxalate co-precipitation method yielding single-phase oxalate precursors. X-ray diffraction, Raman spectroscopy, and Fourier-transform infrared spectroscopy are used to characterize the precipitated oxalates. Simultaneous thermal gravimetric analysis and differential scanning calorimetry reveal a two-step decomposition of the oxalates into the doped oxide. The ionic conductivity of the samples is measured from 250 °C to 600 °C using electrochemical impedance spectroscopy. All samples exhibit similar grain conductivity values at 600 °C, comparable to singly doped samples. However, an increase in total conductivity is observed with an increase in doping concentration up to 15% followed by a decrease beyond this concentration. These findings suggest that multicomponent doping may not significantly enhance the grain conductivity of doped ceria beyond conventional single and co-doped compositions but can modulate the grain boundary conductivity and thus the total conductivity of ceria ceramics.

Influence of Rare-Earth Doping Content and Type on Phase Transformation and Transport Properties in Highly Doped CeO2

“…Similarly, Kalland et al investigated the La 2– x Nd x Ce 2 O 7 series ( x = 0.0, 0.5, 1.0, 1.5, and 2.0) and found that an increase in Nd content led to the appearance of the C-type phase . Double or multiple doping in CeO 2 -based materials can induce a high-entropy effect, potentially extending the solid solution range and leading to the emergence of the C-type structure at higher doping concentrations. , …”

“…33 Double or multiple doping in CeO 2 -based materials can induce a high-entropy effect, potentially extending the solid solution range and leading to the emergence of the C-type structure at higher doping concentrations. 34,35 Regarding lattice cell parameters, a clear shift of the diffraction peaks to higher angles is detected as the rareearth size becomes smaller La 3+ (1.16 Å), Nd 3+ (1.109 Å), Sm 3+ (1.079 Å), Gd 3+ (1.053 Å), and Yb 3+ (0.985 Å), all in an 8fold coordination (Figure 1a−c). Within the same series, for a particular rare-earth, an increase in dopant content would typically lead to a higher cell parameter due to the smaller size of Ce 4+ (0.97 Å) compared to that of any rare-earth element (Table S1).…”

Enhanced Mechanical and Electromechanical Properties of Compositionally Complex Zirconia Zr1–x(Gd1/5Pr1/5Nd1/5Sm1/5Y1/5)xO2−δ Ceramics

“…1−3 These are single-phase metal oxides consisting of five or more different cations in an equal or nearequal atomic percent, i.e., the entropy of mixing ΔS mix higher than ≈1.5 kB/f.u that are integrated on the same crystallographic lattice site. 4,5 HEOs have a large number of tuning spaces in composition and crystal structures, offering new perspectives for tailoring their material properties. 6,7 In 2015, R o s t e t a l .…”

“…In recent years, an entirely different family of a material class, known as compositionally complex oxides (CCOs) or high entropy oxides (HEOs), has attracted significant attention in the ceramics science community, and are mainly derived from the concept of ‘high entropy’ from high entropy alloys or multicomponent alloys. − These are single-phase metal oxides consisting of five or more different cations in an equal or near-equal atomic percent, i.e., the entropy of mixing Δ S mix higher than ≈1.5 kB/f.u that are integrated on the same crystallographic lattice site. , HEOs have a large number of tuning spaces in composition and crystal structures, offering new perspectives for tailoring their material properties. , In 2015, Rost et al synthesized the first HEOs (Mg 0.2 Co 0.2 Ni 0.2 Cu 0.2 Zn 0.2 )­O, with a rock-salt structure that shows a reversible mixing/demixing behavior upon heating and cooling, respectively, and is truly entropy stabilized . Following this seminal work, the realm of HEOs was explored in different oxide systems, including fluorites, spinels, perovskites, rutiles, pyrochlores, and beyond.…”