Pr Cations Research Articles

Crystal structure, composition and valence state of cations in mixed-valence A1-xCdxMnO3 (A=Pr, La) ceramics

Abstract Complex manganites A1−xCdxMnO3 (A = Pr, La) are synthesized by solid state reaction method. X-ray diffraction, scanning electron microscopy and energy-dispersive analysis are applied to study their crystal structure, surface morphology, elemental and phase composition. X-ray photoelectron spectroscopy (XPS) methods are used to study the charge states of Pr and La cations, as well as to quantify the fractions of coexisting Mn3+ and Mn4+ ions. La3d-, La4d-, Pr4d- и Mn2p-spectra of La3+, Pr3+, Mn3+ and Mn4+ ions are calculated in the isolated–ion approximation with accounting for multiplet splitting and charge transfer effect. Good agreement with the experiment is obtained. The relative fractions of trivalent and tetravalent manganese ions in La0.45Cd0.78Mn0,9O2.86 and Pr0.50Cd0.76Mn0.86O2.88 samples are determined by fitting the Mn2p spectra by superposition of experimental spectra containing only Mn3+, and only Mn4+ ions; they were found to be 0.71Mn3+/0.29Mn4+ and 0.54Mn3+/0.46Mn4+, respectively.

Catalytic Activity of LnCo0.5Ni0.5O3-Δ (Ln = La, Pr, Nd) "Positrodes" on Ceramic Protonic Electrolytes

Proton-conducting solid-oxide electrolyzers and fuel cells represent viable, intermediate-temperature green energy conversion and storage technologies. Interest in this class of materials as electrolytes stems from their high ionic conductivity and inherent advantages in the gas flow configuration over traditional solid oxide cells in which the electrolyte is an oxygen ion conductor. However, their commercial viability has been hindered, in part, by the development of corresponding single-phase electrode components with mixed proton-electron conductivity and effective catalytic activity toward oxygen reduction and evolution reactions (ORR/OER). This paper investigates the origin of catalytic activity in LnCo0.5Ni0.5O3-δ (Ln=La, Pr and Nd) perovskites positrodes (positive electrode) by low energy-ion scattering (LEIS) and DFT studies. LEIS results reveal that La, Pr, and Pr cations dominate the outer atomic layer, with profound implications for catalytic activity. Whereas First principle calculations were performed using the plane-wave DFT method and hybrid HSE06 functional suggest, the catalytic activity and electronic properties depend on the valence shell structure of the Ln-site cation and their redox properties.AcknowledgmentsThe authors gratefully acknowledge financial support through JSPS KAKENHI Grant-in-Aid for Scientific Research (C), No. 19K05672, NEDO (International collaboration work in the field of clean energy) JPNP20005, the International Institute for Carbon-Neutral Energy Research (I2CNER) sponsored by the World Premier International Research Center Initiative (WPI),

Separation of heavy (dysprosium) and light (praseodymium, neodymium) rare earth elements using electrodialysis

This work reports electrodialysis studied to separate dysprosium (Dy, a heavy rare earth element (REE)) from praseodymium and neodymium (Pr, Nd, a mixture of light REEs). A unique electrodialysis setup comprising a cation exchange membrane, a PC-400D membrane (anion exchange membrane that transfers large organic anions), and an anion exchange membrane is used. To achieve the separation of these REEs, ethylenediaminetetraacetic acid disodium salt dihydrate is used as the chelating agent. Because of the higher stability constant of EDTA with Dy(III) compared with Pr(III) and Nd(III), most of EDTA form [Dy-EDTA]− chelate which upon applying electric potential move from the feed to the concentrate compartment through the PC-400D membrane, leaving behind free Pr and Nd cations in the feed compartment. The effect of rinse solution concentration (sodium sulfate, 0.05–0.07 mol/L), applied electric potential (10–14 V), feed pH (2–5), and EDTA concentration (EDTA/Dy molar ratio of 0.9–1.2) on key performance indicators of electrodialysis, i.e., purity, yield, separation factor, and Dy removal efficiency is investigated. Rinse solution concentration has a negligible effect on the separation performance in the studied range. Applied potential shows a positive effect on the Dy removal efficiency, but separation factor decreases with increasing potential above 12 V. The suitable pH range for maximum separation performance is found to be above 3 and below 5. Increasing EDTA/Dy molar ratio increases the amount of Pr and Nd chelates with EDTA, which also move to the concentrate compartment and decrease the product purity. The ratio 1:1 is found to result in the highest Dy purity and separation factor. The rinse solution concentration of 0.05 mol/L with 12 V applied potential, pH 4, and EDTA/Dy molar ratio of 1.0 result in a separation factor of 125 which is promising. Under this set of conditions, a Dy purity of 93% and Dy yield of 77% is achieved.

X-Ray Photoelectron Spectroscopy Study of Host/Dopant Cation’s Valence State and Formation of F+-Centers in Pr-Doped CeO2 Nanomaterials

Ce[Formula: see text]Pr[Formula: see text]O2 ([Formula: see text], 0.02, 0.04, 0.06, and 0.08) nano-materials synthesized using co-precipitation method have been investigated mainly for electronic structure properties in this manuscript. Findings and supporting studies are presented to understand the role of valence states of host and dopant cations information of F[Formula: see text] centers through X-ray photoelectron spectroscopy (XPS). Sustained cubic fluorite system confirmed by X-ray diffraction (XRD) analysis and red-shifting of energy gap by UV–Vis spectroscopy in all the samples are our findings. Samples further implored by XPS indicate incidence of cerium and Pr cations in both the oxidation states of 4[Formula: see text] and 3[Formula: see text], respectively. Finally, it has been observed that optical, electronic structure and magnetic properties of CeO2 nanomaterials can be modified by Pr-doping, promising better yield samples with good amount of ferromagnetism for potential uses in the technological applications like spintronics, optoelectronics, and photocatalytic.

Understanding Temperature Stability of Surface Cation Dopants on LSCF Electrodes

State-of-the-art solid oxide fuel cell (SOFC) oxygen electrode materials such as La0.6Sr0.4Co0.2Fe0.8O3-δ (LSCF) continue to be plagued by degradation primarily through strontium (Sr) segregation to the electrode surface and subsequent passivating poisoning reactions with chromium- and sulfur-containing species. Surface infiltration of more oxidizable cations is of interest for LSCF electrodes in order to reduce the electrostatic driver of Sr segregation and due its reported success in reducing Sr segregation and electrochemical degradation on LSC electrodes. In this work, we investigate the thermal stability of Hf, Nd, and Pr infiltrated cations at porous LSCF electrode surfaces. These select cations are of interest as surface infiltrates due to their more oxidizable nature. We demonstrate that infiltrated Hf, Nd, and Pr cations are not thermally stable at the LSCF electrode surface at standard SOFC operating temperatures, diffusing substantially away from the surface above 800°C.

Solvothermal Synthesis, Structural Characterization and Optical Properties of Pr-Doped CeO2 and Their Degradation for Acid Orange 7.

Pr-doped CeO2 with different doping levels was prepared from Ce(NO3)3∙6H2O and Pr(NO3)3∙6H2O by solvothermal method without any additional reagents, in which the mixed solution of ethylene glycol and distilled water was employed as a solvent. The influences of Pr-doping on phase composition, crystal structure and morphology were investigated, as well as Pr valence and oxygen vacancy defects. The Pr cations entered into the CeO2 crystal lattice with normal trivalence and formed a Pr-CeO2 solid solution based on the fluorite structure. The larger trivalent Pr was substituted for tetravalent Ce in the CeO2 crystal and compensated by oxygen vacancy defects, which caused the local lattice expansion of the crystal lattice. Moreover, the Pr-doped CeO2 solid solutions exhibited visible color variation from bright cream via brick red to dark brown with the increasing of Pr contents. The degradation of AO7 dye was also investigated using a domestic medical ultraviolet lamp; the removal efficiency of AO7 by 1% and 2% Pr-doped CeO2 approached 100%, much higher than 66.2% for undoped CeO2.

Synthesis of Fe–Pr co-doped ZnO nanoparticles: Structural, optical and antibacterial properties

In the present work, we studied the role of Fe and Pr addition on the structural, optical and antibacterial properties of spherical ZnO nanoparticles synthesized via sol gel method. The lattice constants values increased, while the average crystallite size decreases as the Pr concentration varies from 0.00 to 0.04. The Fe and Pr cations insertion in the Wurtzite structure were also confirmed by the changes in Zn–O bond length (1.9763 Å to 1.9793 Å for 0.00 ≤ y ≤ 0.04). Raman and FTIR spectroscopies validated the ZnO single-phase formation, and the analysis suggests the existence of oxygen vacancies. The samples showed agglomerated spherical morphology and formation of nanoplate homogeneously organized, while the textural properties were affected by the Fe inclusion. All samples presented band gap values lower than expected for bulk ZnO and the lowest values were obtained for samples containing Fe and Pr. The analysis and deconvolution of photoluminescence spectra confirmed the structural defects formation, caused by the synthesis conditions used and dopants ions inclusion. The antimicrobial activity against Escherichia coli and Staphylococcus aureus using the direct contact method showed superior activity for S. aureus due to the nanoparticles-bacteria interactions. The synergistic effect of dopants may have contributed to the better performance observed against S. aureus, while the Pr concentration directly influenced the inhibitory effect of E. coli. Therefore, the synthesized materials are promising to eliminate pathogenic microorganisms.

Designing Hybrid Mesoporous Pr/Tannate-Inbuilt ZIF8-Decorated MoS2 as Novel Nanoreservoirs toward Smart pH-Triggered Anti-corrosion/Robust Thermomechanical Epoxy Nanocoatings.

For the first time, organic tannic acid (TA) molecules and then inorganic praseodymium (Pr) cations as corrosion inhibitors were successfully loaded into a zeolitic imidazolate framework (ZIF8)-type porous coordination polymer (PCP) decorated on molybdenum disulfide, MoS2, (MS)-based transition metal dichalcogenides (TMDs) to create novel hybrid mesoporous Pr/TA-ZIF8@MS nanoreservoirs. Thereafter, the hybrid nanoreservoirs were embedded into the epoxy matrix for the preparation of smart pH-triggered nanocoatings. Characterizations of the Pr/TA-ZIF8@MS nanoreservoirs via Fourier transform infrared (FT-IR), X-ray diffraction (XRD), thermogravimetric (TG), Brunauer-Emmett-Teller (BET), and field emission-scanning electron microscopy (FE-SEM)/energy-dispersive X-ray spectroscopy (EDS) experiments confirmed the fabrication of mesoporous structures comprising Pr/TA interfacial interactions with ZIF8-decorated MS nanoplatelets possessing high thermal stability and compact/dense configuration features with a framework reorientation. A remarkable smart release of the inhibited cations (Pr3+ and Zn2+) in the presence of inbuilt TA at both acidic and alkaline media was achieved under inductively coupled plasma (ICP) examination. The superior pH-triggered self-healing inhibition through the smart controlled-release of Pr, tannate, Zn, and imidazole inhibited species/complexes from EP/Pr-TA-ZIF8@MS via ligand exchange was obtained from electrochemical impedance spectroscopy (EIS) assessments of the scratched coatings during 72 h of saline immersion. In addition, the long-term barrier-induced corrosion prevention (log |Z|10mHz = 10.49 Ω·cm2 after 63 days) of the EP/Pr-TA-ZIF8@MS was actualized. Moreover, efficient increments of the coating cross-link density (56.45%), tensile strength (63.6%), and toughness value (56.5%) compared to the Neat epoxy coating revealed noticeable thermomechanical properties of the EP/Pr-TA-ZIF8@MS.

Synthesis and chromatic properties of high color performance Prx-ZrSiO4 (x = 0–0.1) yellow pigment

In this paper, high color performance Pr cation doped zircon (Pr-ZrSiO4) yellow pigment has been prepared by inorganic sol-gel method. Meanwhile, the detailed process parameters for preparation of Pr-ZrSiO4 pigment were systematically investigated. The research results indicate that the optimal process parameters are Pr-doping amount of 6 mol.%, calcination temperature of 900 °C, holding time of 2 h and Si/Zr ratio of 1.05. The synthesized Pr-ZrSiO4 pigment shows an intense yellow hue, which chromatic parameters are L* = 81.84, a* = 4.36, b* = 70.55 and C* = 70.68. Moreover, the pigment shows outstanding tinting performance for ceramic glaze, suggesting its attractive application in ceramic decoration. XPS analysis demonstrated that the Pr cations in the Pr-ZrSiO4 pigment consists of two valence states, namely trivalent and tetravalent. Finally, heterogeneously distributed behavior of Pr cations in the pigment was discovered.

Optical properties of a new (1−x)Bi1/2Na1/2TiO3 + xPr1/2Na1/2TiO3 solid solution system

The solid solutions of Bi1/2Na1/2TiO3 and Pr1/2Na1/2TiO3 materials were successfully synthesized by a simple chemical method. X-ray diffraction measurements of the Pr1/2Na1/2TiO3-modified Bi1/2Na1/2TiO3 materials indicated that Pr1/2Na1/2TiO3 was well dissolved into the host Bi1/2Na1/2TiO3 materials, resulting in the random incorporation of Pr cations in the host materials. The optical bandgap of the Pr1/2Na1/2TiO3-modified Bi1/2Na1/2TiO3 materials slightly reduced as increasing Pr1/2Na1/2TiO3 concentrations, from 3.04 eV for the pure Bi1/2Na1/2TiO3 material to 2.95 eV for the sample with 9 mol.% of Pr1/2Na1/2TiO3. We observed strong photoluminescence emission at 610 nm in the Pr1/2Na1/2TiO3-modified Bi1/2Na1/2TiO3 system, which originated from electron transitions from 3P0 to 3H6 levels of Pr3+ cations. We expected that our work would provide a simple method to combine photoluminescence properties in lead-free ferroelectric materials for smart electronic device applications.

Oxygen transport in Pr nickelates: Elucidation of atomic-scale features

Pr2NiO4+δ oxide with a layered Ruddlesden–Popper structure is a promising material for SOFC cathodes and oxygen separation membranes due to a high oxygen mobility provided by the cooperative mechanism of oxygen migration involving both interstitial oxygen species and apical oxygen of the NiO6 octahedra. Doping by Ca improves thermodynamic stability and increases electronic conductivity of Pr2−xCaxNiO4+δ, but decreases oxygen mobility due to decreasing the oxygen excess and appearing of 1–2 additional slow diffusion channels at x ≥ 0.4, probably, due to hampering of cooperative mechanism of migration. However, atomic-scale features of these materials determining oxygen migration require further studies. In this work characteristics of oxygen diffusion in Pr2−xCaxNiO4+δ (x = 0–0.6) are compared with results of the surface analysis by X-ray photoelectron spectroscopy and modeling of the interstitial oxygen migration by the plane-wave density functional theory calculations. According to the X-ray photoelectron spectroscopy data, the surface is enriched by Pr for undoped sample and by Ca for doped ones. The O1s peak at ~531 eV corresponding to a weakly bound form of surface oxygen located at Pr cations disappears at ~500 °C. Migration of interstitial oxygen was modeled for a I4/mmm phase of Pr2NiO4+δ. The interstitial oxygen anion repulses the apical one in the NiO6 octahedra pushing it into the tetrahedral site between Pr cations. The calculated activation barrier of this migration is equal to 0.585 eV, which reasonably agrees with the experimental value of 0.83 eV obtained by the oxygen isotope exchange method. At the same time, for the model compound Ca2NiO4+δ, obtained by isomorphic substitution of Pr by Ca in Pr2NiO4+δ, calculations implied formation of the peroxide ion comprised of interstitial and lattice oxygen species not revealed in the case of incomplete substitution (up to PrCaNiO4+δ composition).Hence, calculations in the framework of the plane-wave density functional theory provide a realistic estimation of specificity of oxygen migration features in Pr2NiO4+δ doped by alkaline-earth metals.

Design of materials for solid oxide fuel cells cathodes and oxygen separation membranes based on fundamental studies of their oxygen mobility and surface reactivity

Design of materials for solid oxide fuel cells cathodes and oxygen separation membranes and studying their oxygen transport characteristics are important problems of modern hydrogen energy. In the current work, fundamentals of such materials design based on characterization of their oxygen mobility by oxygen isotope exchange with C18O2 and 18O2 in flow and closed reactors for samples of Ruddlesden – Popper-type oxides Ln2-xCaxNiO4+δ, perovskite-fluorite nanocomposites PrNi0.5Co0.5O3-δ – Ce0.9Y0.1O2-δ, etc. are presented. Fast oxygen transport was demonstrated for PNC – YDC (DO ~10-8 cm2/s at 700°C) nanocomposites due to domination of the fast diffusion channel involving oxygen of the fluorite phase with incorporated Pr cations and developed perovskite-fluorite interfaces. For LnCNO materials a high oxygen mobility (DO ~10-7 cm2/s at 700°C) provided by the cooperative mechanism of its migration was demonstrated. Depending on Ca dopant content and Ln cation nature, in some cases 1–2 additional channels of the slow diffusion appear due to decreasing the interstitial oxygen content and increasing the energy barrier for oxygen jumps due to cationic size effect. Optimized by the chemical composition and nanodomain structure materials of these types demonstrated a high performance as SOFC cathodes and functional layers in asymmetric supported oxygen separation membranes.

Promoted methane activation on doped ceria via occupation of Pr(4f) states

Steam reforming of the methane stream obtained from biomass gasification is a potential route for sustainable syngas (CO + H2) and hydrogen production. The rate-limiting step for the reactions involved in methane steam reforming (MSR) is thought to be CH4 activation. Praseodymium-doped ceria-based catalysts, with easily reducible Pr cations and high oxygen storage capacity, could be attractive for MSR. In this work, we performed density functional theory (DFT) calculations to examine the activity of a low Pr-doped CeO2(1 1 1) surface for methane reforming. The results show a significant lowering (0.48 eV) of the energy barrier for methane activation via homolytic H3CH bond cleavage. This can be mainly explained by the easy occupation of Pr(4f) gap states by electrons transferred from adsorbed hydrogen species. The promotion of methane activation upon Pr doping of ceria was corroborated with methane temperature-programed reduction (CH4-TPR) experiments conducted in both Ce0.95Pr0.05O2 and CeO2 samples.

Corrosion inhibition properties of a green hybrid pigment based on Pr-Urtica Dioica plant extract

The main aim of this research is studying the corrosion inhibition properties of the combination of praseodymium nitrate (PrN) and Urtica Dioica (UrDi) on mild steel in sodium chloride solution. Fourier transform infrared (FT-IR), ultraviolet-visible (UV-Vis), thermogravimetric analysis/differential thermogravimetry (TGA/DTG) and X-ray photoelectron spectroscopy (XPS) results confirmed complex formation between Pr cations and UrDi (Pr-UrDi). Electrochemical results revealed that the Pr-UrDi hybrid complex had significant influence on the mild steel corrosion protection (by inhibition efficiency of ca. 94%) in NaCl solution.

Templated Synthesis of Pr-Doped Ceria with Improved Micro and Mesoporosity Porosity, Redox Properties and Catalytic Activity

A Ce0.9Pr0.1O2 catalyst has been prepared using nitrates as metal precursors, which have been infiltrated into a polymethylmethacrylate colloidal crystal template and calcined at 500 °C. Its catalytic activity for CO oxidation (4.3 μmolCO s−1 gcatalyst −1 at 300 °C) is far superior compared to a reference catalyst prepared in the same way but without the template (1.4 μmolCO s−1 gcatalyst −1 at 300 °C), and even superior to a three dimensionally ordered macroporous (3DOM) catalyst prepared forming metal citrates to obtain the macroporous structure into the template (0.7 μmolCO s−1 gcatalyst −1 at 300 °C). It is demonstrated that infiltration of nitrates into the colloidal crystal template is more positive for catalytic oxidation of CO than formation of the 3DOM structure using citrates, despite the collapse of the macroporous structure. The 3DOM catalyst prepared with citrates has lower surface area (51 m2 g−1) than catalysts prepared using nitrates (118 and 87 m2 g−1 for the infiltrated and non infiltrated catalysts, respectively). The infiltrated catalyst prepared with nitrates reaches the highest surface area, and also develops more micro and mesoporosity and presents smaller crystallite size (8 vs. 16 nm) than the counterpart non infiltrated catalyst. In addition, the population of oxygen vacancies is also much higher in the infiltrated catalyst prepared with nitrates, and it is postulated that this improves oxygen mobility into the mixed oxide lattice and favors the catalyst reduction. On the contrary, it has been ruled out any effect of the infiltration step in the insertion of Pr cations into the ceria lattice.

Correlations between Oxygen Uptake and Vacancy Concentration in Pr-Doped CeO2

The oxygen uptake of a series of Pr–CeO2 materials was measured using thermogravimetric analysis at 420 and 600 °C, and at both temperatures, 20% Pr–CeO2 was found to have the highest uptake. The materials were characterized using X-ray diffraction and scanning transmission electron microscopy. Defects in the materials were identified using Raman spectroscopy, and ultraviolet–visible spectroscopy was used to show the presence of Pr cations in the +3 oxidation state. The existence of these species was attributed to be responsible for the ability of the materials to uptake oxygen. Electron energy loss spectroscopy was used to investigate the effect of Pr addition to CeO2; the Ce M5/M4 and O IB/IC ratios were calculated to indicate the relative changes in the Ce3+ and oxygen vacancy concentration, respectively. There was no observable increase in the Ce3+ concentration; however, the oxygen vacancy concentration increased with an increase in the Pr content. Thus, Pr increases the defect concentration and the ability of the materials to uptake oxygen.

Study of magnetic ordering in the perovskite manganites Pr0.6Sr0.4CrxMn1-xO3

Powder samples of the ABO3 perovskite manganites Pr0.6Sr0.4CrxMn1-xO3 (0.00≤x≤0.30) were synthesized using the sol-gel method. X-ray diffraction analyses showed that all the samples had a single-phase orthorhombic structure. By analyzing magnetic parameters on the basis of the O2p itinerant electron model, we found that there are two magnetic transition temperatures, TCM and TCP, corresponding to changes in the magnetic ordering for the Mn and Pr cations, respectively. The magnetic moments of Mn3+ and Cr3+ cations within the B sublattice show canted ferromagnetic coupling, and the magnetic moments of the Pr cations within the A sublattice also show canted ferromagnetic coupling. However, the total magnetic moment of the A sublattice shows antiferromagnetic coupling against that of the B sublattice. The assumption of the canted ferromagnetic coupling within the B sublattice was confirmed using magnetoresistance experimental results.

Redox behavior of a low-doped Pr-CeO2(111) surface. A DFT+U study

In this work, we investigated the redox behavior (donation and replenishing of oxygen) of a low praseodymium (Pr)-doped CeO2(111) surface. We considered a 3.7at.% Pr doping and performed density functional calculations using the GGA formalism with the ‘U’ correction on Ce(4f) and Pr(4f) orbitals. Our results indicate that Pr doping promotes oxygen donation by lowering the energy necessary to form surface anionic vacancies. When the Ce0.963Pr0.037O2(111) surface donates one oxygen, the two excess electrons locate on Pr and Ce cations and reduce them to Pr3+ and Ce3+ ones. Praseodymium doping also favors the activation of O2 molecule on surface O-holes, leading to formation of a superoxide (O2−) radical as well as to reoxidation of the Ce3+ cation to Ce4+ one. Additionally, we used the CO molecular adsorption for testing the reactivity of those superoxide species. The calculations expose the ability of these radicals to oxidize CO forming a CO2 molecule floating on the surface. However, when the superoxide is in the immediate vicinity of Pr dopant a carbonate-type species is formed. Our theoretical results may help to gain insight into redox properties and improved catalytic performance of low-doped Pr-CeO2 solids.

Structural and Transport Properties of the Blc-Pbco System; Effects of Cation Ordering

The drive to reduce the operating temperatures of solid oxide fuel cells (SOFCs) and electrolysers (SOECs) requires the discovery of new materials showing enhanced oxygen transport and electrocatalytic properties. As well as modifying the composition of materials with the simple perovskite structure, lately there has also been interest in materials with other, often, layered structures including the Ruddlesden-Popper type materials, such as La2NiO4, and double perovskites such as GdBaCo2O5 (GBCO) and PrBaCo2O5 (PBCO) [1]. Whilst Sr-substituted lanthanum cobaltite (La0.6Sr0.4CoO3-d, LSC64) is widely used, the Ba-substituted analogue La1-xBaxCoO3-d (BLC) is attracting recent interest showing competitive electrode performances [2,3]. On the other hand, the double perovskite PrBaCo2O5+d (PBCO) has high diffusivity and surface exchange activity, which is often attributed to the anisotropic diffusion of oxygen due to the ordering of Pr and Ba cations on the A-site. However, experimental measurements suggest that the degree of anisotropy between diffusion in along the c axis and in the ab plane is only around half an order of magnitude [4]. Therefore, the family of compositions between single perovskite BLC and double perovskite PBCO offers an interesting system to study the effects of cation ordering on transport behaviour. In this work, we have studied the structural and oxygen transport properties of materials in the La0.5-x/2Prx/2Ba0.5CoO3-d compositional space. The materials were synthesised by a conventional solid state reaction route, and X-ray diffraction revealed that Pr-rich compositions (0.7 < x < 1) retain the same double perovskite structure as PBCO, with cation ordering on the A-site, and hence more properly written as La1-xPrxBaCo2O5+d. The La-rich compositions (0 < x <0.7) showed a cubic symmetry, similar to the Sr-analogue LSC64. Oxygen isotope exchange studies on the Ba0.5La0.5CoO3 end member show that the oxygen tracer diffusion (D*) and exchange (k*) coefficients are similar to those of PBCO, and of Sm0.5Sr0.5CoO3, which are some of the highest reported [5], explaining the high electrochemical performance of the single perovskite material [2,3]. Preliminary results indicate these values change only slightly across the composition field, with no significant increase as the structure changes from single to double perovskite. These findings seem to suggest that it is not the A-cation ordering in the crystal structure of PBCO that provides per se its high performance, but the defect chemistry, namely the high concentration of oxygen vacancies in the material.

Sm-doped praseodymium nickelates-cobaltites and their nanocomposites with Y-doped ceria as promising cathode materials

ABSTRACTThis work aims at elucidating effects of composition and microstructure of materials based upon Pr1-ySmyNi1-xCoxO3-δ perovskites on their oxygen mobility. Pr1-ySmyNi1-xCoxO3-δ and their composites with Y-doped ceria are perspective materials for intermediate temperature solid oxide fuel cells and oxygen separation membranes. Doping PrNi1-xCoxO3-δ by Sm results in suppression of the fast channel of oxygen diffusion along extended defects due to Sm segregation in their vicinity. For nanocomposites moderate doping by Sm enhances fast oxygen diffusion in fluorite phase domains and along perovskite-fluorite interface due to a higher disordering caused by incorporation of both Pr and Sm cations into Y-doped ceria.