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High-temperature transport properties of the PrBaFe2O6−δ ceramics, prepared by different routes, were studied in the light of their potential use in energy conversion technologies. The PrBaFe2O6−δ oxides fabricated at 1000 °C and at 1350 °C are referred to as LTS and HTS, respectively, as synthesized at relatively low and high temperatures. The LTS oxide was shown to have a better oxygen exchange ability than HTS, starting oxygen release at a temperature ~ 200 °C lower when heating and adopting more oxygen when cooling. Dense ceramics were fabricated from the LTS oxide by a method, preserving the enhanced oxygen exchange ability. The electrical conductivity of the ceramics was measured by a four-probe DC technique as a function of oxygen partial pressure at 750–950 °C. The measurement results were analyzed using the data on charge carrier concentration revealed from the previously obtained data on oxygen content versus oxygen partial pressure. The mobility characteristics of n- and p-type carriers in PrBaFe2O6−δ were found to be practically unaffected by synthesis temperature. The average electron mobility was calculated to be ~ 0.007 cm2V−1s−1 at the migration energy of 0.5 eV, whereas the mobility and the migration energy of holes were ~ 0.08 cm2V−1s−1 and ~ 0.2 eV, respectively. Unlike electron carriers, the mobility of oxygen ions in PrBaFe2O6−δ was found to be affected by synthesis temperature. The average values of oxygen mobility and migration energy were determined to be ~ 1.1·10−5 cm2V−1s−1 and ~ 0.7 eV for the LTS oxide, whereas ~ 0.7·10−5 cm2V−1s−1 and ~ 0.8 eV for the HTS oxide. The oxygen ion conductivity of PrBaFe2O6−δ was found to reach 0.2 S·cm−1 at 900 °C, which is a characteristic of a high oxygen transport rate. [ABSTRACT FROM AUTHOR]

The article discusses the results of the synthesis of spinel NiCo2O4 by a new method of hydrothermolysis, as well as methods of precipitation of oxalates and ultrasonic aerosol pyrolysis from aqueous solutions of chlorides and nitrates of nickel and cobalt. The preparation conditions for each synthesis method were selected, the morphology of the obtained samples was considered, the porous structure of the material was studied, and the mesoporosity of the powders was estimated. Single-phase spinel NiCo2O4 was obtained only by precipitation of oxalates; two other methods of synthesis, due to higher temperatures of the processes, lead to the appearance of an impurity of nickel–cobalt double oxide and a decrease in the nickel content in the spinel composition. The nature of the porosity of the materials obtained and the morphology depend on the synthesis method: the mesoporous structure in ultrasonic spray pyrolysis, macroporous structure in hydrothermolysis. The sample obtained by the oxalate precipitation method has the maximum specific surface area of 65.40 ± 0.33 m2/g and a pore volume of 0.409 cm3/g. The samples after hydrothermolysis have the minimum specific surface area of 10.22 ± 0.06 m2/g and a porosity of 0.055 cm3/g. The powders synthesized by ultrasonic spray pyrolysis have intermediate values of these characteristics between the other two methods, 41.68 ± 0.13 m2/g and 0.144 m3/g, respectively. Highlights: The methods of thermolysis of oxalates make it possible to obtain pure NiCo2O4. A materials after hydrothermolysis and spraying contain an impurity of nickel–cobalt double oxide. The mesoporous structure is characteristic of spray pyrolysis, macroporous––for hydrothermolysis. Materials of different morphology were obtained: short wires, hollow spheres and flower-like shape. [ABSTRACT FROM AUTHOR]