Pr- and Sm-Substituted Layered Perovskite Oxide Systems for IT-SOFC Cathodes

In this study, the phase synthesis and electrochemical properties of A/A//A///B2O5+d (A/: Lanthanide, A//: Ba, and A//: Sr) layered perovskites in which Pr and Sm were substituted at the A/-site were investigated for cathode materials of Intermediate Temperature-Operating Solid Oxide Fuel cells (IT-SOFC). In the PrxSm1-xBa0.5Sr0.5Co2O5+d (x = 0.1–0.9) systems, tetragonal (x < 0.4) and orthorhombic (x ≥ 0.5) crystalline structures were confirmed according to the substitution amount of Pr, which has a relatively large ionic radius, and Sm, which has a small ionic radius. All of the layered perovskite oxide systems utilized in this study presented typical metallic conductivity behavior, with decreasing electrical conductivity as temperature increased. In addition, Pr0.5Sm0.5Ba0.5Sr0.5Co2O5+d (PSBSCO55), showing a tetragonal crystalline structure, had the lowest conductivity values. However, the Area-Specific Resistance (ASR) of PSBSCO55 was found to be 0.10 Ωcm2 at 700 °C, which is lower than those of the other compositions.

Theoretical prediction by DFT and experimental observation of heterocation-doping effects on hydrogen adsorption and migration over the CeO2(111) surface

The addition of dopants with a small ionic radius led to strong binding of H atoms, and the balance of H+ reactivity (mobility) and H+ coverage was fundamentally important for high H+ conductivity and catalysis involving surface protonics.

Limits of Cation Solubility in AMg2Sb2 (A = Mg, Ca, Sr, Ba) Alloys

A M 2 X 2 compounds that crystallize in the CaAl 2 Si 2 structure type have emerged as a promising class of n- and p-type thermoelectric materials. Alloying on the cation (A) site is a frequently used approach to optimize the thermoelectric transport properties of A M 2 X 2 compounds, and complete solid solubility has been reported for many combinations of cations. In the present study, we investigate the phase stability of the AMg 2 Sb 2 system with mixed occupancy of Mg, Ca, Sr, or Ba on the cation (A) site. We show that the small ionic radius of Mg 2 + leads to limited solubility when alloyed with larger cations such as Sr or Ba. Phase separation observed in such cases indicates a eutectic-like phase diagram. By combining these results with prior alloying studies, we establish an upper limit for cation radius mismatch in A M 2 X 2 alloys to provide general guidance for future alloying and doping studies.

COMPARISON OF THE MAGNETIZATION BEHAVIORS IN PEROVSKITE COMPOUNDS La0.7-xLnxPb0.3MnO3 (Ln=Pr AND Sm)

The magnetization behaviors of two manganite oxide systems, La 0.7-x Ln x Pb 0.3 MnO 3 ( Ln = Pr and Sm ), have been synthesized. The replacement of La ions by Pr or Sm results in a considerable decrease in the ferromagnetic ordering temperature T C and clearly irreversible behavior in the zero-field-cooling-field-cooling curve at a low applied field, showing a short-range spin order phase. These facts are in agreement with the smaller ionic radii of Pr (0.130 nm) and Sm (0.124 nm) ions in contrast to La ion (0.136 nm), and the corresponding larger distortion of perovskite structures. The saturation magnetization M S decreases as Sm content increases relative to the increase of M S as Pr content increases. This can be interpreted in terms of the competition between suppression of ferromagnetism due to structure tuning induced by the small ionic radius of the interpolated cations into the La -site and the increase of ferromagnetically interacting spins due to the introduction of magnetic Pr or Sm ions with f-shell electrons.

The reduction of HCl dissolved in LiCl-KCl eutectic

The cathodic reduction of hydrogen chloride dissolved in LiCl-KCl eutectic has been studied by both chronopotentiometry and linear sweep voltammetry using a platinum electrode. The reduction reaction has been found to proceed by a reversible one-electron transfer process forming a soluble product. ��� Diffusion coefficients calculated from solubility measurements and the electrochemical studies are considerably higher (e.g. 2.1 x 10-4 cm2 s-1 at 793 K) than most other solutes in molten salts but in good agreement with results from a less detailed study. The high value is probably due to the small ionic radius of the proton as compared to other ions in the lattice of the molten salt system.