Ru Substitution Research Articles

Element Strategy Using Ru-Mn Substitution in CuO-CaCu3Ru4O12 Composite Ceramics with High Electrical Conductivity

CaCu3Ru4−xMnxO12 bulks with various substitution amounts x and sintering additive CuO (20 vol.%) were prepared, and the influence of x on the electrical conductivity in a wide temperature range (8–900 K) was investigated. Microstructural observations showed an enhancement of bulk densification upon Mn substitution. Although the resistivity increased with increasing x, the resistivity was as low as a few mΩcm even in the sample with x = 2.00, where half of Ru is substituted by Mn. This high conductivity despite the loss of Ru 4d conduction following the substitution is explained by the A-site (Cu2+) conduction in CaCu3Ru4−xMnxO12. The thermopower of CaCu3Ru4−xMnxO12 was found to be influenced by the substitution, and a sign inversion was observed in the substituted samples at low temperature. The partial substitution of Ru by Mn in CaCu3Ru4O12 enables the reduction of the materials cost while maintaining good electrical conductivity for applications as a conducting device component.

Synthesis of Ru-doped Double Perovskite Anode for SOFC

One of the great current needs for anode material in solid oxide fuel cells is to combine in one redox-resistant compound an efficient multifunctionality, that is, that the same material must exhibit both good catalytic activity and mixed ionic-electronic conductivity. Such a material should ideally be active towards different fuels allowing fuel-flex SOFCs capable to operate using the most convenient fuel available in various situations. Ceramics with perovskite structure are, from this point of view, are promising candidates. Different compounds such as (La,Sr)(Mn,Cr)O and SrMoMgO have been investigated, but more efficient anodes are still required. In this study, the Pr0.5Ba0.5MnO3 was used as the precursor phase of the double perovskite PrBaMn2O5+δ (PBMO), obtained at reducing conditions. The transport and catalytic properties were studied in the pristine compound and in Ru-doped samples Pr0.5Ba0.5Mn1-xRuxO3 (Ru-PBMO). Ru substitution at the B-site is expected to enhance the catalytic properties of the ceramic toward ethanol or methane fuels. Ceramic powders were synthesized by the polymeric precursor method and characterized by thermogravimetric analyses, X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The electrical properties of sintered samples were evaluated by dc 4-probe technique, in the 25 - 800 °C temperature range in both air and reducing conditions. The TG/DTA and XRD data show mass loss stabilization and crystalline phase formation occurring at ~800 °C. The evolution of the XRD pattern upon calcining temperature indicated the formation of single phase of Ru-PBMO samples at ~1100 °C. The initial results suggest that PBMO and PBMO-Ru compounds are promising SOFC anodes.

Ru doping in iron-based pnictides: The “unfolded” dominant role of structural effects for superconductivity

We present an ab-initio study of Ru substitution in two different compounds, BaFe2As2 and LaFeAsO, pure and F-doped. Despite the many similarities among them, Ru substitution has very different effects on these compounds. By means of an unfolding technique, which allows us to trace back the electronic states into the primitive cell of the pure compounds, we are able to disentangle the effects brought by the local structural deformations and by the impurity potential to the states at the Fermi level. Our results are compared with available experiments and show: i) satisfying agreement of the calculated electronic properties with experiments, confirming the presence of a magnetic order on a short range scale; ii) Fermi surfaces strongly dependent on the internal structural parameters, more than on the impurity potential. These results enter a widely discussed field in the literature and provide a better understanding of the role of Ru in iron pnictides: although isovalent to Fe, the Ru-Fe substitution leads to changes in the band structure at the Fermi level mainly related to local structural modifications.

Manganese-induced magnetic symmetry breaking and its correlation with the metal-insulator transition in bilayered Sr3(Ru1−xMnx)2O7

Bilayered Sr3Ru2O7 is an unusual metamagnetic metal with inherently antiferromagnetic (AFM) and ferromagnetic (FM) fluctuations. Partial substitution of Ru by Mn results in the establishment of metal-insulator transition (MIT) at TMIT and AFM ordering at TM in Sr3(Ru1-xMnx)2O7. Using elastic neutron scattering we determined the effect of Mn doping on the magnetic structure and in-plane magnetic correlation lengths in Sr3(Ru1-xMnx)2O7 (x = 0.06 and 0.12). With increasing Mn doping (x) from 0.06 to 0.12 or decreasing temperatures for x=0.12, an evolution from an in-plane short-range to long-range double-stripe AFM ground state occurs. For both compounds, the onset of magnetic correlation with an anisotropic behavior coincides with the sharp rise of the electrical resistivity and the specific heat. Since it does not induce measurable lattice distortion, the double-stripe magnetic order with anisotropic spin texture breaks the symmetry from C4v crystal lattice to C2v magnetic sublattice. These observations shed new light on an age-old question of Slater versus Mott-type MIT.

Synthesis of Ru-doped Double Perovskite Anode for SOFC

Pr0.5Ba0.5MnO3 was studied as the precursor phase of the double perovskite PrBaMn2O5+δ (PBMO) anode material for solid oxide fuel cells (SOFC). The general properties were studied in both the pristine compound and Ru-doped samples Pr0.5Ba0.5Mn1-xRuxO3 (PBMRu). Ru substitution at the B-site is expected to enhance the catalytic properties of the ceramic towards ethanol or methane fuels. The studied compounds were synthesized by the polymeric precursor method and characterized by thermogravimetric analyses, X-rays diffraction (XRD), and electrical transport properties. The experimental data show PBMO phase formation occurring at ~800 °C and single phase compounds at ~1100 °C up to ~10 at.% of Ru substituted. Similar ionic radius of Ru3+ and Mn3+ results in little effect on both the crystalline structure and electrical conductivity as compared to the pristine compound.

Evolution of magnetic and transport properties in hole doped Y2Ir2O7

We report the effect of Ru4+ substitution at Ir-site on structural, magnetic and electrical properties in pyrochlore iridate Y2Ir2O7. Structural investigation has been done using x-ray powder diffraction and Rietveld analysis for both samples. There is no structural phase transition with Ru doping. Magnetization study shows that on slightly substitution of Ru at Ir-site effectively shifts the magnetic irreversible temperature Tirr towards low temperature and reduce the bifurcation between MZFC and MFC branches. The electrical resistivity shows an insulating behavior in whole temperature range, however, resistivity decreases with doping of Ru.

Evolution of structure, magnetism, and electronic transport in the doped pyrochlore iridate Y2Ir2−xRuxO7

The interplay between spin-orbit coupling (SOC) and electron correlation ($U$) is considered for many exotic phenomena in iridium oxides. We have investigated the evolution of structural, magnetic and electronic properties in pyrochlore iridate Y$_2$Ir$_{2-x}$Ru$_{x}$O$_7$ where the substitution of Ru has been aimed to tune this interplay. The Ru substitution does not introduce any structural phase transition, however, we do observe an evolution of lattice parameters with the doping level $x$. X-ray photoemission spectroscopy (XPS) study indicates Ru adopts charge state of Ru$^{4+}$ and replaces the Ir$^{4+}$ accordingly. Magnetization data reveal both the onset of magnetic irreversibility and the magnetic moment decreases with progressive substitution of Ru. These materials show non-equilibrium low temperature magnetic state as revealed by magnetic relaxation data. Interestingly, we find magnetic relaxation rate increases with substitution of Ru. The electrical resistivity shows an insulating behavior in whole temperature range, however, resistivity decreases with substitution of Ru. Nature of electronic conduction has been found to follow power-law behavior for all the materials.

Exploring the influence of iron substitution in lithium rich layered oxides Li2Ru1−xFexO3: triggering the anionic redox reaction

The partial substitution of Ru with Fe in Li2RuO3 stabilises the layered structure during cycling, leading to a stable capacity of ∼250 mA h g–1.

Effect of Ru Substitution on Temperature Coefficient of Resistance and Magnetoresistance Properties of Nd<sub>0.67</sub>Sr<sub>0.33</sub>MnO<sub>3</sub>

The effect of Ru substitution on temperature coefficient of resistance (TCR) and electrical transport properties of Nd0.67Sr0.33Mn1-xRuxO3 (with x = 0, 0.05 and 0.1) manganites prepared by solid state reaction route are studied. Ru substitution at Mn sites leads to reduction in TP and increase the overall MR. The electrical transport mechanisms of these compounds are investigated by using different theoretical models, for temperatures below and above TP. The maximum value of TCR of Nd0.67Sr0.33Mn1-xRuxO3 (x= 0.05 and 0.1) are found to be higher compared to pristine compound. For memory device and bolometer IR detectors application point of view, all samples show the maximum magnetoresistance (MR) of 81 % at 5 T applied magnetic field, while the temperature coefficient of resistance (TCR) is found to ~17% K-1.

The study on the eect of Ruthenium(Ru) in LaFeAsO

We study the eect of Ru substitution at Fe site on LaFe1ô€€€xRuxAsOcompounds for x = 0, 0.25, 0.50, 0.75 and 1. We produce densityof state (DOS), Fermi surface (FS) and a band structure based onDensity Functional Theory(DFT). The result on the band structuresshow that Ru substitution changes the hole bands and not the elec-tron bands. One of the possible reason is perhaps that Ru substitutiondoes not induce additional electrons, which is in agreement with NMRand resistivity measurement report. We conclude that the change inthe whole bands is the reason for suppressing eect of Ru. The DOSis much aected for over doped region(x > 0:50) around the Fermilevel. For Ru = 0.50, the Fermi surfaces is close to nesting, and wecalculated the value of Tc applying McMillan equation. The result in-dicates that the alloy can be a superconductor only for strong pairingpotential( > 0:7).

The Abnormal Optical Property and Room‐Temperature Exchange Bias Behavior in Na‐ and Ru‐Codoped BiFeO3 Nanoparticles

Bi0.98Na0.02Fe1−xRuxO3 (x = 0, 0.01, 0.02) samples were prepared via a sol–gel method. The formation of the desired materials was confirmed using X‐ray diffraction. The tetravalent Ru doping could effectively reduce the number of oxygen vacancy, and subsequently reduce the leakage current. Interestingly, the optical band gap was narrowed gradually in our samples, which seems contradictory with the variation in oxygen vacancy. To better understand this abnormal optical property, the effect of bandwidth was analyzed based on the change in Fe–O bond length and Fe–O–Fe bond angle, and the corresponding phenomenological qualitative model was proposed. The magnetization was increased with Ru substitution. In addition, an exchange bias (EB) phenomenon without field cooled process was observed at room temperature for all the samples, which was explained by introducing a core–shell structure model. Moreover, the EB behavior becomes more pronounced at 5 K for 1% Ru‐doped sample.

Enhanced electrochemical performances of layered LiNi0.5Mn0.5O2 as cathode materials by Ru doping for lithium-ion batteries

The pristine and Ru-doped LiNi0.5Mn0.5O2 cathode materials are synthesized by a wet chemical method, followed by a high-temperature calcination process. The influence of Ru substitution on the microstructure and electrochemical performances of the prepared materials are investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and galvanostatic charge/discharge test. The XRD results show that, compared to the Ru-undoped sample, the LiNi0.5Mn0.45Ru0.05O2 owns a better hexagonal α-NaFeO2 structure and a smaller amount of cation mixing. The galvanostatic charge/discharge measurements demonstrate that the electrochemical properties of the LiNi0.5Mn0.5O2 sample are enhanced by Ru doping. At 5 and 10 C, the discharge capacity of LiNi0.5Mn0.45Ru0.05O2 is 118.61 and 105.43 mAh g−1, respectively, which is higher than those of LiNi0.5Mn0.5O2 (101.24 and 78.94 mAh g−1) due to the reduced charge-transfer resistance and the improved lithium-ion diffusion coefficient. On the basis of these results, Ru doping is considered an effective way to enhance the electrochemical performances of LiNi0.5Mn0.5O2 cathode materials.

Correlation between topological band character and chemical bonding in a Bi14Rh3I9-based family of insulators

Recently the presence of topologically protected edge-states in Bi14Rh3I9 was confirmed by scanning tunnelling microscopy consolidating this compound as a weak 3D topological insulator (TI). Here, we present a density-functional-theory-based study on a family of TIs derived from the Bi14Rh3I9 parent structure via substitution of Ru, Pd, Os, Ir and Pt for Rh. Comparative analysis of the band-structures throughout the entire series is done by means of a unified minimalistic tight-binding model that evinces strong similarity between the quantum-spin-Hall (QSH) layer in Bi14Rh3I9 and graphene in terms of -molecular orbitals. Topologically non-trivial energy gaps are found for the Ir-, Rh-, Pt- and Pd-based systems, whereas the Os- and Ru-systems remain trivial. Furthermore, the energy position of the metal -band centre is identified as the parameter which governs the evolution of the topological character of the band structure through the whole family of TIs. The -band position is shown to correlate with the chemical bonding within the QSH layers, thus revealing how the chemical nature of the constituents affects the topological band character.

Fabrication and electrochemical properties of LiCo1-xRuxO2 cathode materials for Li-ion battery

LiCo1-xRuxO2 (where x = 0.0–0.5) are prepared by conventional solid–state reaction technique. The effect of Ru substitutions on the structural properties and electrochemical performance of LiCoO2 cathode materials is investigated in detail. The XRD analysis shows that increasing Ru content in LiCoO2 above x = 0.1 causes formation of different phases such as Li1.4RuO3, Li2Ru0.5Co0.5O3 and RuO2 which are used in the Li- ion batteries as an electrode materials. It is found in the XRD analysis that the Ru doping causes a decrease in the crystallite size which is important for improving the battery performance. The CV analysis shows that the Ru doping till x = 0.1 can produce an improvement in the performance of the cell and the capacity retention after 50 cycle is much better than that of the cell that fabricated using the pure LiCoO2.

Influences of Ru Substitution for Mn on Magnetic Properties and Charge Ordering Phase of La<SUB>0.4</SUB>Ca<SUB>0.6</SUB>MnO<SUB>3</SUB>

Influences of Ru Substitution for Mn on Magnetic Properties and Charge Ordering Phase of La<SUB>0.4</SUB>Ca<SUB>0.6</SUB>MnO<SUB>3</SUB>

Itinerant to localized electronic behavior in phase segregated ruthenates

Simultaneous doping of Ba and Zr for Sr and Ru in SrRuO3 leads to phase separation of orthorhombic SrRuO3 (SRO) and nine layer rhombohedral BaRuO3 (9R-BRO). Differences in ionic radius and electronegativity between the cations are responsible for the chemical phase separation with increase of doping concentration. Random substitution of Ru by Zr localizes electron and induces Metal-Insulator (M−I) transition for lower doping concentration (5% and 10%). Electron–electron interaction dominates electrical conduction process due to cationic disorder in SRO lattice. Dilution of ferromagnetic interaction due to non-magnetic element Zr decreases both Curie temperature and Curie-Wiess constant and produces Griffiths phase just above the Curie temperature. At higher doping concentration (40%), solid solution of ruthenates reveals magnetism purely related to 9R-BRO phase.

Lorentz transmission electron microscopy on nanometric magnetic bubbles and skyrmions in bilayered manganites La1.2Sr1.8(Mn1−yRuy)2O7 with controlled magnetic anisotropy

We have investigated nanometric magnetic textures in thin (<150 nm) plates of Ru-doped bilayered manganites La1.2Sr1.8(Mn1−yRuy)2O7. Ru substitution for Mn site changes the magnetic anisotropy from in-plane to out-of-plane easy axis type without any significant change of global magnetic and crystal structures. The combination of conventional and Lorentz transmission electron microscopy observations confirms the emergence of magnetic bubbles and skyrmions in the absence of magnetic field. With the changing Ru concentration, systematic changes in the type of magnetic bubbles are observed. A tiny residual magnetic field also affects the generation and the type-change of magnetic bubbles.

In-plane electronic anisotropy in the antiferromagnetic orthorhombic phase of isovalent-substitutedBa(Fe1−xRux)2As2

We have studied the anisotropy in the in-plane resistivity and the electronic structure of isovalent Ru-substituted ${\mathrm{BaFe}}_{2}{\mathrm{As}}_{2}$ in the antiferromagnetic-orthorhombic phase using well-annealed crystals. The anisotropy in the residual resistivity component increases in proportion to the Ru dopant concentration, as in the case of Co-doped compounds. On the other hand, both the residual resistivity and the resistivity anisotropy induced by isovalent Ru substitution are found to be 1 order of magnitude smaller than those induced by heterovalent Co substitution. Combined with angle-resolved photoemission spectroscopy results, which show almost the same anisotropic band structure for both the parent and the Ru-substituted compounds, we confirm the scenario that the anisotropy in the residual resistivity arises from anisotropic impurity scattering in the magnetostructurally ordered phase rather than directly from the anisotropic band structure of that phase.

Fragile structural transition inMo3Sb7

Mo$_3$Sb$_7$ single crystals lightly doped with Cr, Ru, or Te are studied in order to explore the interplay between superconductivity, magnetism, and the cubic-tetragonal structural transition. The structural transition at 53\,K is extremely sensitive to Ru or Te substitution which introduce additional electrons, but robust against Cr substitution. No sign of a structure transition was observed in superconducting Mo$_{2.91}$Ru$_{0.09}$Sb$_7$ and Mo$_3$Sb$_{6.975}$Te$_{0.025}$. In contrast, 3at\% Cr doping only slightly suppresses the structural transition to 48\,K while leaving no trace of superconductivity above 1.8\,K. Analysis of magnetic properties suggests that the interdimer interaction in Mo$_3$Sb$_7$ is near a critical value and essential for the structural transition. All dopants suppress the superconductivity of Mo$_3$Sb$_7$. The tetragonal structure is not necessary for superconductivity.

High Catalytic Activity of Ru@CoSe2/C toward Oxygen Reduction Reaction

Carbon supported Ru@CoSe2 nanoparticles (Ru@CoSe2/C) were prepared through a simple and facile two-step route. The CoSe2 nanoparticles were first obtained by microwave assisted method, and then followed by galvanic substitution of Ru on CoSe2. It was found that the introduction of a small amount of Ru into CoSe2 led to a core-satellite like structure in which the disordered Ru nanoparticles were adsorbed on CoSe2 nanocrystallites. Compared with CoSe2/C and Ru85Se15/C, the Ru@CoSe2/C exhibited higher catalytic activity toward oxygen reduction reaction due to the enhanced Ru utilization through Ru and CoSe2 interaction. The half-wave potential of 0.548 V (vs. RHE) and the cathodic current density of 3.37 mA cm-2 at 0.6 V were obtained for Ru@CoSe2/C in an acidic solution.