High-temperature oxygen non-stoichiometry, conductivity and structure in strontium-rich nickelates La2-xSrxNiO4-\delta (x = 1 and 1.4)

Oxygen nonstoichiometry, electrical conductivity and thermal expansion of La2 xSrxNiO4-\delta phases with high levels of strontium substitution (1 =< x =< 1.4) have been investigated in air and oxygen atmosphere in the temperature range 20-1050 degrees C. These phases retain the K2NiF4-type structure of La2NiO4 (tetragonal, space group I4/mmm). The oxygen vacancy fraction was determined independently from thermogravimetric and neutron diffraction experiments, and is found to increase considerably on heating. The electrical resistivity, thermal expansion and cell parameters with temperature show peculiar variations with temperature, and differ notably from La2NiO4$\pm$\delta in this respect. These variations are tentatively correlated with the evolution of nickel oxidation state, which crosses from a Ni3+/Ni4+ to a Ni2+/Ni3+ equilibrium on heating

Synthesis and characterization of La_0.8Sr_1.2Co_0.5M_0.5O_4-? (M=Fe, Mn)

The M4+-containing K2NiF4-type phases La0.8Sr1.2Co0.5Fe0.5O4 and La0.8Sr1.2Co0.5Mn0.5O4 have been synthesized by a sol-gel procedure and characterized by X-ray powder diffraction, thermal analysis, neutron powder diffraction and Mössbauer spectroscopy. Oxide ion vacancies are created in these materials via reduction of M4+ to M3+ and of Co3+ to Co2+. The vacancies are confined to the equatorial planes of the K2NiF4-type structure. A partial reduction of Mn3+ to Mn2+ also occurs to achieve the oxygen stoichiometry in La0.8Sr1.2Co0.5Mn0.5O3.6. La0.8Sr1.2Co0.5Fe0.5O3.65 contains Co2+ and Fe3+ ions which interact antiferromagnetically and result in noncollinear magnetic order consistent with the tetragonal symmetry. Competing ferromagnetic and antiferromagnetic interactions in La0.8Sr1.2Co0.5Fe0.5O4, La0.8Sr1.2Co0.5Mn0.5O4 and La0.8Sr1.2Co0.5Mn0.5O3.6 induce spin glass properties in these phases

Highly sensitive coulometric titration of oxygen for the characterization of solid materials at elevated temperatures

A new setup for characterization of solid material oxygen exchange and conductivity in a broad oxygen partial pressure range and at elevated temperatures is presented. The development target of this setup is directed towards the detection of ultra-low amounts of exchanged oxygen. For this, electrochemical cells made of yttria-stabilized zirconia (YSZ) were optimized and applied in a flow-through arrangement. The design and process measures enable a lower limit of detection below 100&thinsp;pmol of exchanged oxygen. Furthermore, the system characteristics concerning oxygen dispersion, titration efficiency and electrode kinetics are described.</p

Resistance to amorphisation in Ca1-xLa2x/3TiO3 perovskites – a bulk ion-irradiation study

The changes induced from 1 MeV Kr+ and 5 MeV Au+ ion irradiation at room temperature have been utilised to determine the impact of cation vacancies on the radiation damage response of bulk Ca1-xLa2x/3TiO3 perovskite structured ceramics. Perovskite systems have long been considered as candidate waste forms for the disposition of actinide wastes, and doping with multi-valent elements such as Pu may lead to cation deficiency. Based on GAXRD and TEM analysis, two regions of resistance/susceptibility to amorphisation have been confirmed with reference to CaTiO3. Increased resistance to amorphisation has been observed for 0.1 ≤ x ≤ 0.4, with an increased susceptibility to amorphisation for x ≥ 0.5. It is proposed that these processes are induced by enhanced recovery from radiation damage for 0.1 ≤ x ≤ 0.4, and reduced tolerance for disorder/the increasingly covalent nature of the A-O bond for x ≥ 0.5. Lattice parameter analysis of the x = 0 and 0.5 samples showed a saturation in radiation damage induced volume swelling at 4.7 ± 0.1% and 1.8 ± 0.1%, respectively, while the saturation limit for the b parameter was lower than the respective a and c orthorhombic parameters. In the x = 0.2 and 0.4 samples, amorphisation was not observed, however the b parameter was found to swell to a lesser extent than the a and c parameters. Swelling was not observed for the ion irradiated x ≥ 0.6 samples

Mechanism for enhanced oxygen reduction kinetics at the (La,Sr)CoO3−δ/(La,Sr)2CoO4+δ hetero-interface

The recently reported fast oxygen reduction kinetics at the interface of (La,Sr)CoO3−δ (LSC113) and (La,Sr)2CoO4+δ (LSC214) phases opened up new questions for the potential role of dissimilar interfaces in advanced cathodes for solid oxide fuel cells (SOFCs). Using first-principles based calculations in the framework of density functional theory, we quantitatively probed the possible mechanisms that govern the oxygen reduction activity enhancement at this hetero-interface as a model system. Our findings show that both the strongly anisotropic oxygen incorporation kinetics on the LSC214 and the lattice strain in the vicinity of the interface are important contributors to such enhancement. The LSC214(100) surface exposed to the ambient at the LSC113/LSC214 interface facilitates oxygen incorporation because the oxygen molecules very favorably adsorb onto it compared to the LSC214(001) and LSC113(001) surfaces, providing a large source term for oxygen incorporation. Lattice strain field present near the hetero-interface accelerates oxygen incorporation kinetics especially on the LSC113(001) surface. At 500 °C, 4 × 102 times faster oxygen incorporation kinetics are predicted in the vicinity of the LSC113/LSC214 hetero-interface with 50% Sr-doped LSC214 compared to that on the single phase LSC113(001) surface. Contributions from both the anisotropy and the local strain effects are of comparable magnitude. The insights obtained in this work suggest that hetero-structures, which have a large area of (100) surfaces and smaller thickness in the [001] direction of the Ruddlesden–Popper phases, and larger tensile strain near the interface would be promising for high-performance cathodes

ВЛИЯНИЕ МЕТОДА ПОЛУЧЕНИЯ НА АДСОРБЦИОННЫЕ СВОЙСТВА НАНОСТРУКТУРИРОВАННОГО ПОРОШКА MgO

Magnesium oxide is widely used as an adsorbent, catalyst, identifier of chemical and toxic pollutants, in water and gas purification processes. Mesoporous magnesium oxide powder has been synthesized by the method of deposition, spray pyrolysis and glycine-citrate-nitrate method, their crystal structure, microstructure, granulometric composition and adsorption properties have been studied. Optimal conditions for the production of magnesium oxide by the glycine-citrate-nitrate method have been determined, which make it possible to obtain a powder with average primary particle sizes of 12 nm and the smallest sizes of secondary particles starting from 70 nm. The influence of the method of obtaining nanostructured magnesium oxide powder on the physicochemical properties is established. High values of the total pore volume of 1.038 cm3 /g exhibited the MgO powder obtained by the precipitation method.Оксид магния находит широкое применение в качестве адсорбента, катализатора, идентификатора загрязняющих химических и токсических веществ, в процессах водо- и газоочистки. В настоящей работе методом осаждения, распылительного пиролиза и глицин-цитрат-нитратным методом синтезированы мезопористые порошки оксида магния, изучена их кристаллическая структура, микроструктура, гранулометрический состав и адсорбционные свойства. Определены наиболее оптимальные условия получения оксида магния глицин-цитрат-нитратным методом, которые позволяют получить порошок со средними размерами первичных частиц 12 нм и наименьшими размерами вторичных частиц – от 70 нм. Установлено влияние способа получения на адсорбционные свойства наноструктурированного порошка оксида магния. Высокие значения общего объема пор 1,038 см3 /г продемонстрировал порошок MgO, полученный методом осаждения

СИНТЕЗ И АДСОРБЦИОННЫЕ СВОЙСТВА НАНОСТРУКТУРИРОВАННЫХ ПОРОШКОВ Mg(OH)2 И MgO

Magnesium oxide has found applications as adsorbent, catalyst and ideutifier of the contamination of chemicals and toxic substances in the processes of water and gases purification. In this work, mesoporous magnesium hydroxide and oxide were synthesized from water solutions by easy and cheap wet chemistry method. Crystal structure, particle size distribution and adsorption properties of the synthesized powders were studied. Obtained powders of Mg(OH)2 and MgO showed sufficiently high total pore volume – 0.737 and 1.038 cm3 /g, respectively, which opens an opportunity to use them as nanoreactors for the synthesis of isolated nanosized particles and multidirection catalysts. Оксид магния находит широкое применение в качестве адсорбента, катализатора, идентификатора загрязняющих химических и токсических веществ, в процессах водо- и газоочистки. В настоящей работе методом осаждения синтезированы мезопористые порошки гидроксида и оксида магния, изучена их кристаллическая структура, микроструктура, гранулометрический состав и адсорбционные свойства. Полученные порошки Mg(OH)2 и MgO продемонстрировали высокие значения общего объема пор – 0,737 и 1,038 см3 /г соответственно, что открывает широкие возможности их использования в качестве нанореакторов для синтеза наноразмерных изолированных частиц и создания на их основе полимаршрутных катализаторов.

Interaction of perovskite type lanthanum-calcium-chromites-titanates La1-xCaxCr1-yTiyO3-δ with solid electrolyte materials

Lanthanum-calcium-chromites-titanates have been proposed as alternative anode material, and diffusion barrier layer material for metal supported cells3, due to their electrical conductivity and acceptable coefficients of thermal expansion. However interactions of perovskites with electrolyte materials such as doped zirconia are known to cause zirconate formation depending on temperatures and oxygen partial pressure 4. In this study we demonstrate how the presence of metallic nickel at the phase boundary affects the zirconate formation at the solid state perowskite-fluorite interface. Different compositions of La1-xCaxCr1-yTiyO3-δ (x = 1, 0.95, 0.7, 0.6, 0.5, 0.4; y = 1, 0.9, 0.8) were synthesized and reactivity with yttria doped zirconia (8YSZ) and nickel-8YSZ-cermets have been investigated by means of X-ray diffraction, field emission scanning electron microscopy and energy dispersive X-ray spectroscopy after 80 hours at 1300 °C in reducing atmosphere (H2). The results indicate that under certain conditions there is no zirconate formation in the absence of nickel, whereas if nickel is present at the interface, calcium- and or lanthanum zirconate formation take place, depending on the La/Caratio of the A-site doping. Thermodynamic calculation and EDX spectra consistently indicate nickel-titanium alloy formation as a reason for the destabilization of the perovskite lattice within a range of 10-19.4 < a(O2) < 10-16.5 at 1300 °C