Double Perovskite-type Oxide Research Articles

Magnetic ordering of divalent europium in double perovskites Eu 2LnTaO 6 ( Ln=rare earths) : Magnetic interactions of Eu 2+ ions determined by magnetic susceptibility, specific heat, and 151Eu Mössbauer spectrum measurements

Structures and magnetic properties of double perovskite-type oxides Eu 2 LnTaO 6 ( Ln=Eu, Dy–Lu) were investigated. These compounds adopt a distorted double perovskite structure with space group P2 1/ n. Magnetic susceptibility, specific heat, and 151Eu Mössbauer spectrum measurements show that the Eu 2+ ions at the 12-coordinate sites of the perovskite structure are antiferromagnetically ordered at ∼4 K, and that Ln 3+ ions at the 6-coordinate site are in the paramagnetic state down to 1.8 K.

Characterization of Perovskite-Type Anode Materials: Sr2-xLaxFeMoO6-δ (x = 0-0.5) for SOFCs

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Thermal expansion and electrochemical properties of Ni-doped GdBaCo 2O 5+ δ double-perovskite type oxides

Layered GdBaCo 2 −x Ni x O 5 + δ (0 ≤ x ≤ 0.3) complex oxides were synthesized and investigated as cathodes for intermediate-temperature solid oxide fuel cell (IT-SOFCs). All compositions formed an orthorhombic double-perovskite structure after calcination at 1000 °C for 5 h. The thermal expansion coefficient (TEC) was effectively decreased due to the partial substitution of Ni for Co, but the cathodic polarization resistance slightly increased with the increasing Ni content. Among the tested oxides, the GdBaCo 1.7Ni 0.3O 5 + δ composition showed a fairly reduced TEC (15.5 × 10 −6 K −1) and reasonably low polarization resistances (e.g., 0.54 Ωcm 2 at 600 °C), which was considered as a promising candidate for IT-SOFCs.

Partial oxidation of methane to syngas over the catalyst derived from double perovskite (La 0.5Sr 0.5) 2FeNiO 6− δ

Double perovskite-type oxide (La 0.5Sr 0.5) 2FeNiO 6− δ (LSFN) was invented as the precursor of a catalyst for the partial oxidation of methane (POM). The catalyst derived from LSFN is the K 2NiF 4-supported Ni(0) system, where K 2NiF 4 denotes the oxide (La 0.5Sr 0.5) 2Ni 1− x FeO 4+ δ , a chemically stable structure with mixed ionic and electronic conducting properties. Among the four catalysts derived from LSFN, the best catalyst showed a high CH 4 conversion ( X C H 4 > 99 % ), high syngas selectivity (>98%) and, most importantly, nil coke formation at 900 °C. Detailed structural characterizations revealed that the presence of a small amount of SrCO 3, left initially by incomplete formation of LSFN, and of nano-Ni(0) domains (or clusters <5 nm on average) on the K 2NiF 4 support is vital to this extraordinary catalytic performance. Furthermore, the decrease of H 2/CO molar ratio with the increase in methane conversion happening in the course of activation was simulated using a group of the proposed key reaction steps of POM.

Synthesis and characterization of carbon dioxide and boiling water stable proton conducting double perovskite-type metal oxides

In this paper, we report the synthesis, chemical stability and electrical properties of three new Ta-substituted double perovskite-type Ba 2Ca 2/3Nb 4/3O 6 (BCN). The powder X-ray diffraction (PXRD) confirms the formation of double perovskite-like structure Ba 2(Ca 0.75Nb 0.59Ta 0.66)O 6− δ , Ba 2(Ca 0.75Nb 0.66Ta 0.59)O 6− δ and Ba 2(Ca 0.79Nb 0.66Ta 0.55)O 6− δ . The PXRD of CO 2 treated (800 °C; 7 days) and water boiled (7 days) samples remain the same as the as-prepared samples, suggesting a long-term structural stability against the chemical reaction. The electrical conductivity of the investigated perovskites was found to vary in different atmospheres (air, dry N 2, wet N 2, H 2 and D 2O + N 2). The AC impedance investigations show bulk, grain-boundary and electrode contributions in the frequency range of 0.01 Hz to 7 MHz. Below 600 °C, the bulk conductivity in wet H 2 and wet N 2 was higher than in air, dry H 2 and dry N 2. However, an opposite trend was observed at high temperatures, which may be ascribed to p-type electronic conduction. The electrical conductivity of the investigated perovskites was decreased in D 2O + N 2 compared to that of H 2O + N 2 atmosphere. This clearly shows that the investigated Ta-doped BCN compounds exhibit proton conduction in wet atmosphere which was found to be consistent with water uptake. The water uptake was further confirmed by thermogravimetric analysis (TGA) and Fourier transform infrared spectroscopy (FTIR) characterization. Among the samples investigated, Ba 2(Ca 0.79Nb 0.66Ta 0.55)O 6− δ shows the highest proton conductivity of 4.8 × 10 −4 S cm −1 (at 1 MHz) at 400 °C in wet (3% H 2O) N 2 or H 2, which is about an order of magnitude higher than the recently reported 1% Ca-doped LaNbO 4 at the same atmosphere and at 10 kHz.