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Ceria (CeO2) and its solid solutions with Gd2O3 are technologically important and environmentally friendly materials with numerous interesting properties and important applications. Nevertheless, the magnetic properties of ceria are even today not fully understood, and magnetoelastic coupling in pure or doped ceria remains essentially unexplored. This has been so, in part, due to the difficulty of measuring very small magnetostrictive strains in weakly paramagnetic materials. During the last decade, however, technical advances have enabled sensitive and accurate measurements of sample deformation in high magnetic fields. Here, forced magnetostriction (MS) in Gd2O3‐CeO2 solid solution ceramics (Ce1−xGdxO2−x/2, 0 ≤x≤ 1) at room temperature is characterized. In a pulsed magnetic field μ0H≤ 60 Tesla, longitudinal MS strain is observed to depend on the square of the field amplitude and to increase linearly with Gd3+ concentration but is not sensitive to the lattice symmetry of the ceramics. The theory attributes the origin of the observed strain to the single‐ion MS response of Gd3+ to the crystal field via mixing of ground and excited electronic states and covalent hybridization with oxygen ligands. Contributions of charge‐compensating oxygen vacancies and/or Van Vleck paramagnetism to the observed magnetoelastic coupling are determined to be negligible. [ABSTRACT FROM AUTHOR]

Flash sintering was discovered in 2010, where a dog‐bone‐shaped zirconia sample was sintered at a furnace temperature of 850°C in <5 s by applying electric fields of ~100 V cm−1 directly to the specimen. Since its discovery, it has been successfully applied to several if not all oxides and even ceramics of complex compositions. Among several processing parameters in flash sintering, the electrical parameters, i.e., electric field and electric current, were found to influence the onset temperature for flash and the degree of densification respectively. In this work, we have systematically investigated the influence of the electrical parameters on the onset temperature, densification behavior, and microstructure of the flash sintered samples. In particular, we focus on the development of a processing map that delineates the safe and fail regions for flash sintering over a wide range of applied current densities and electric fields. As a proof of concept, gadolinium‐doped ceria (GDC) is shown as an example for developing of such a processing map for flash sintering, which can also be transferred to different materials systems. Localization of current coupled with hot spot formation and crack formation is identified as two distinct failure modes in flash sintering. The grain size distribution across the current localized and nominal regions of the specimen was analyzed. The specimens show exaggerated grain growth near the positive electrode (anode). The region adjacent to the negative electrodes (cathode) showed retarded densification with large concentration of isolated pores. The electrical conductivity of the flash sintered and conventional sintered samples shows identical electrical conductivity. This quantitative analysis indicates that similar sintering quality of the GDC can be achieved by flash sintering at temperature as low as 680°C. [ABSTRACT FROM AUTHOR]

This study aims to understand the effect of the electrical field on microstructure evolution during field‐assisted sintering or spark plasma sintering (FAST/SPS) of 10 mol% gadolinium‐doped ceria (GDC) with experimental and numerical methods. The novelty of this study has been the observation of enhanced grain growth in the region closer to the anode, even under FAST/SPS conditions with electrical fields less than 5 V/cm. The grain growth kinetics, including determination of activation energy and grain‐boundary mobility, were analyzed along the cross section of the samples for different temperatures and dwell periods. With an increase in distance from the anode, reduction in the activation energy for grain growth and grain‐boundary mobility was observed. These observations attributed to the attraction of oxygen ions to the anode region under an electrical field with an increase in defects along the grain boundaries. Thereby an increase in the grain‐boundary mobility and larger grains in that region were observed. A homogenous microstructure was observed in a case where the current did not flow through the sample. Furthermore, a numerical strategy has also been developed to simulate this behavior in addition to heat generation, heat transfer, and densification using Finite Element Methods (FEM) simulations. The simulation results provided an insight into the presence of a potential difference across the cross section of the samples. The simulation results were also in good agreement with the experimental observations. [ABSTRACT FROM AUTHOR]

A dense Ce0.9Gd0.1O2−d (GDC) interlayer is an essential component of the SOFCs to inhibit interfacial elemental diffusion between zirconia‐based electrolytes (eg YSZ) and cathodes. However, the characteristic high sintering temperature of GDC (>1400°C) makes it challenging to fabricate an effective highly dense interlayer owing to the formation of more resistive (Zr,Ce)O2 interfacial solid solutions with YSZ at those temperatures. To fabricate a useful GDC interlayer, we studied the influence of transition metal (TM) (Co, Cu, Fe, Mn, & Zn) doping on the sintering and electrochemical properties of GDC. Dilatometry data showed dramatic drops in the necking and final sintering temperatures for the TM‐doped GDCs, improving the densification of the GDC in the order of Fe > Co > Mn > Cu > Zn. However, the electrochemical impedance data showed that among various transition metal dopants, Mn doping resulted in the best electrochemical properties. Anode supported SOFCs with Mn‐doped, nano, and commercial‐micron GDC interlayers were compared with regard to their performance and stability levels. Although all of the SOFCs showed stable performance, the SOFC with the Mn‐doped GDC interlayer showed the highest power density of 1.14 W cm−2 at 750°C. Hence, Mn‐doped GDC is suggested for application as an effective diffusion barrier layer in SOFCs. [ABSTRACT FROM AUTHOR]

Abstract: GdxCe1‐xO2‐δ (GDC) nanoparticles were synthesized, using continuous hydrothermal flow synthesis. By varying the synthesis conditions, particle size and morphology could be tailored. Here, particle sizes between 6 and 40 nm with polyhedral or octahedral shape could be obtained. Gd0.2Ce0.8O2‐δ nanoparticles were further processed into inks for inkjet printing. Despite the small particle size/large surface area, inks with excellent printing behavior were formulated. For proof‐of‐concept, thin GDC layers were printed on a) green NiO‐GDC substrates, and on b) presintered NiO‐YSZ substrates. While no dense layers could be obtained on the green NiO‐GDC substrates, GDC nanoparticles printed on NiO‐YSZ substrates formed a dense continuous layer after firing at 1300°C. [ABSTRACT FROM AUTHOR]

The anode materials used in solid oxide fuel cells at intermediate temperature (IT-SOFC) consist of a mixture of nickel and cerium oxide doped with rare earth, forming a composite with a conductor metal and a ceramic with ionic conductivity. Nickel catalysts supported on gadolinium-doped ceria were prepared in this work in order to obtain materials with catalytic properties suitable for their use as anodes in IT-SOFC. The catalysts were evaluated in steam reforming of methane. It was noted that gadolinium caused an increase in the metal-support interaction and in the resistance to sintering of metal particles. Although the carbon content is not reduced, the carbon deposited in the 30CG10 catalyst is more reactive due to its amorphous nature, and it can therefore be regenerated at temperatures lower than 400 °C. [ABSTRACT FROM AUTHOR]