The synthesis of Nd2−xCaxCoO4±δ at T=900–1200°C in air at atmospheric pressure was performed by solid state synthesis and freeze drying synthesis methods. Single phase solid solutions were observed at 0.6≤x≤1 and T=1200°C. At T<1100°C the range of solid solutions formation was drastically reduced to 0.9<x<1.05. Exact position of solid solution domain boundaries is varied with synthesis method that points to the exceptional influence of kinetic factors on the phase formation processes.

The electrochemical properties of Pr2CuO4 (PCO) electrode screen-printed on Ce0.9Gd0.1O1.95 (CGO) electrolyte were investigated. PCO was synthesized by a solid-state route from the stoichiometric mixture of oxides at 1273 K, 20 h. Thermogravimetric analysis (TGA) of PCO both in air and Ar demonstrated its stability up to 1173 K. X-ray powder diffraction study of the PCO-CGO mixture annealed in air at 1173 K for 100 h did not reveal chemical interaction between materials. The oxygen reduction on porous PCO electrodes applied on CGO electrolyte was studied in a symmetrical cell configuration by AC impedance spectroscopy at OCV conditions at 773-1173 K and p(O2) = 10(-4)-1 atm. Analysis of the data revealed that depending on temperature and oxygen partial pressure different rate-determining steps of the overall oxygen reduction reaction take place. Calculated value of area specific resistance (ASR) of PCO electrode is 1.7 +/- 0.2 Omega cm(2) at 973 K in air and it is constant after 6 subsequent thermocycles. We have found that oxygen reduction on PCO applied on CGO takes mainly place at the triple-phase boundary (TPB) since Adler-Lane-Steele (ALS) model is not valid. Therefore electrochemical characteristics of PCO electrode can be improved by further optimization of both microstructure of the electrode and electrode/electrolyte interface and PCO can be considered as a promising cathode material for intermediate temperature solid oxide fuel cells (IT-SOFC). Copyright (c) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.

High-temperature crystal structure of the layered cuprates Ln2CuO4, Ln=Pr, Nd and Sm with tetragonal T′-structure was refined using X-ray powder diffraction data. Substantial anisotropy of the thermal expansion behavior was observed in their crystal structures with thermal expansion coefficients (TEC) along a- and c-axis changing from TEC(a)/TEC(c)≈1.37 (Pr) to 0.89 (Nd) and 0.72 (Sm). Temperature dependence of the interatomic distances in Ln2CuO4 shows significantly lower expansion rate of the chemical bond between Pr and oxygen atoms (O1) belonging to CuO2-planes (TEC(Pr–O1)=11.7ppmK−1) in comparison with other cuprates: TEC (Nd–O1)=15.2ppmK−1 and TEC (Sm–O1)=15.1ppmK−1. High-temperature electrical conductivity of Pr2CuO4 is the highest one in the whole studied temperature range (298–1173K): 0.1–108S/cm for Pr2CuO4, 0.07–23S/cm for Nd2CuO4 and 2×10−4–9S/cm for Sm2CuO4. The trace diffusion coefficient (DT) of oxygen for Pr2CuO4 determined by isotopic exchange depth profile (IEDP) technique using secondary ion mass spectrometry (SIMS) varies in the range 7.2×10−13cm2/s (973K) and 3.8×10−10cm2/s (1173K) which are in between those observed for the manganese and cobalt-based perovskites.

The structural and transport properties of the layered cuprate Pr 2 CuO 4 have been studied in the temperature range 300–2100 K using molecular dynamics simulation. The first evidence is presented for a premelting effect in Pr 2 CuO 4 : disordering on one of its oxygen sites and abnormally fast oxygen diffusion at temperatures above 1700 K. We have clarified the microscopic mechanism of oxygen ion transport in this material. The large oxygen diffusion coefficient ( D > 10 −7 cm 2 /s) obtained in our simulations of the layered cuprate Pr 2 CuO 4 suggests that it has considerable potential as a host for electrode materials with mixed ionic-electronic conductivity.

The cuprates La 2 − x Sr 1 + x Cu 2 O 6 + δ ( x = 0, 0.1, 0.2) are synthesized by solid-state method. Their dc conductivity was studied over the 373 to 1173 K temperature range and 10 to 2.1 × 10 4 Pa oxygen partial pressure range by using four-probe technique. It is shown that the cuprate conductivity in air is maximal at ∼673 K; it is 60 S/cm for La 2 SrCu 2 O 6.09 ; 68 S/cm, for La 1.9 Sr 1.1 Cu 2 O 6.18 ; and 81 S/cm, for La 1.8 Sr 1.2 Cu 2 O 6.10 . The thermal expansion coefficient of La 2 SrCu 2 O 6.09 is determined by thermomechanical method and high-temperature X-ray diffraction method; its value (16 ppm K −1 ) shows that the material is compatible with the ceria-based solid electrolytes during the thermal cycling.

Complex cuprates La0.85Sr0.15CuO2.5−δ having an anion-deficient perovskite structure and La2−x Sr x CuO4−δ (x = 0.15, 0.6, 1.0) having a K2 NiF4 layered structure have been prepared by ceramic technology. X-ray powder diffraction verified that single-phase samples were obtained. X-ray photoelectron spectroscopy (XPS) was used to determine the surface composition of compacted samples. It was found that both the photoionization cross-section and the photoelectron mean free path should be taken into account when calculating the surface composition. The surface was enriched in strontium as a result of segregation, regardless of the bulk composition of the cuprate sample.