Ir Doping Research Articles

Altering magnetic and optical features of rare earth orthoferrite LuFeO3 ceramics via substitution of Ir into Fe sites

LuFeO3 and LuFe1-xIrxO3 ceramics with x ​= ​0.05 and 0.10 have been obtained by solid-state reaction process. Scanning electron microscope (SEM) analyses have revealed the existence of both particle agglomeration and porosity of nature of the studied samples. The X-ray photoelectron spectroscopy (XPS) investigations have revealed that while Lu has 3+, Fe has mix valence states, 2+ and 3+. On the other hand, the Ir dopant has metallic and 4+ valence states in the study samples. The Raman investigations unveiled i) the Raman peak intensity reduces with Ir doping until ∼600 ​cm−1, ii) the peaks appearing between 200 ​cm−1 and 600 ​cm−1 wavenumbers shift toward the smaller values. Magnetic measurements, conducted by vibrating sample magnetometer (VSM), have shown the spin re-orientation (SR) transition temperature around 47 ​K for all the investigated samples. Furthermore, it is noticed the 5 ​mol % Ir doped sample has higher magnetization than other samples owing to existence of magnetic impurities such as Lu3Fe5O12. M ​− ​H loops have unveiled that Ir doping advances both Hc and Mr values compared to the undoped LFO sample. This increase in both Hc and Mr values could be due to 1) the variation of the canted angels of Fe3+ moments, 2) the advancement of energy of magnetocrystalline anisotropy, and 3) formation of secondary phases such as Lu3Fe5O12 and Fe3O4. Furthermore, the optical band gap examinations have revealed that the band gap of LFO reduces from 2.19 ​eV to 2.

Interface structure characterization and elements doping on interface bonding strength and tensile failure mechanism of NiCo coating/Cu matrix

The interface bonding strength is one of the most important properties of coatings, which is significantly affected by the interface microstructure. By electron backscatter diffraction technology, it was determined that the grain orientation relationship of coating and matrix at interface is dominated by Cu 〈101〉/NiCo 〈101〉, some of Cu 〈101〉/NiCo 〈101〉 grains contain a certain twist angle, range of 0 to 63.5°. On this basis, using the first principles calculation to predict the Cr, Os, and Ir doping on the interface bonding strength and the tensile failure mechanism of NiCo coating. Heat of segregation shows that the doping elements have no tendency to diffuse to the matrix and interface. Work of separation reveals that the Cu(101)/NiCo(101) interface has good bonding strength (3.758 eV), stronger than Cu (2.203 eV), weaker than NiCo (4.860 eV) and the Cr doping at Co2 site and Os doping at Ni3 site can improve the interface bonding strength. The ideal tensile test reveals that Cr and Os doping can increase the max tensile strength of NiCo coating (along the 〈101〉 direction), and Cr doping increased by 34%. The analysis of atomic position and bond length shows that the tensile failure occurs inside the Cu atom layers. By the electron properties, the strengthening effect is attributed to the enhanced covalent properties between the Cr-Ni or Co atoms. The electron location function and charge density map intuitively reflect the origin of crack of interface structure in the stretching process. In summary, the Cr and Os doping not only strengthen the tensile strength of NiCo coating itself, but also improve the interface bonding strength, which is worthy of further study.

Investigation of Local Structure and Enhanced Thermal Stability of Ir-Doped PdRu Nanoparticles for Three-Way Catalytic Applications

The local structure and thermal stability of newly synthesized PdRuIr and PdRu alloy nanoparticles (NPs) were studied using X-ray absorption fine structure spectroscopy (XAFS) and compared with those of Ru NPs. Pd K-edge XAFS reveals that a significant fraction of Pd segregates, forming metal NP clusters. In the PdRuIr NPs, a small fraction of Pd forms an alloy with Ir, whereas a majority phase is Ru–Ir alloy having the novel face-centered cubic structure. Apart from the distinct local surroundings, XAFS analysis revealed the presence of an anharmonic disorder in the PdRu and PdRuIr NPs. The previously observed enhanced thermal stability with Pd and Ir doping was investigated using temperature-dependent in situ XAFS. In the Ru NPs, an abrupt change in the near-edge features was observed at 673 K, which was gradually suppressed for PdRu and PdRuIr NPs. At this temperature, the dynamical fluctuations were more pronounced in the pure Ru NPs, helping to convert surface-adsorbed O2 into the volatile RuO4 phase, thereby leading to earlier evaporation of Ru. Dynamical fluctuation suppresses with alloying elements or gets extended to a higher temperature, helping to delay the RuO4 formation process and enhancing the thermal stability of the PdRu and PdRuIr NPs in increasing order.

Mesoporous Spinel Ir-doped NiCo2O4 Nanostructure as an Efficient Catalyst for Oxygen Evolution Reaction

Water electrolysis (WE) is an attractive advanced technology for the production of H2. A key issue in the WE is to develop suitable catalysts for the oxygen evolution reaction (OER), where a relatively large energy loss occurs. The Ir-doped NiCo2O4 catalysts exhibit the formation of a solid solution and a porous nanostructure. The oxygen vacancies formed by Ir doping can enhance the electrocatalytic activity for the OER owing to increased electrical conductivity and tunable adsorption energies of OH- and H2O. In comparison to IrO2 as a representative OER catalyst, the Ir(10 at%) doped NiCo2O4 catalyst (10-Ir-NCO) exhibits the better OER performance (overpotential of 303 mV at 10 mA cm−2) and its stability for 20,000 s. In addition, in the overall water splitting test, the 10-Ir-NCO || Pt/C exhibits the excellent OER activity (a low overpotential of 0.5 V at 100 mA cm−2) and stability (20 h at 50 mA cm−2).

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

Confined Ir single sites with triggered lattice oxygen redox: Toward boosted and sustained water oxidation catalysis

Influence of iridium (Ir) doping on the structural, electrical, and dielectric properties of LuFeO3 perovskite compound

Rare-earth ferrites have been intensively investigated owing to their magnetic, electrical, and optical features in the literature. The present quest goals to examine the electrical properties of LuFeO3 (LFO) and LuFe1−xIrxO3 (LFIO) ceramics with different mol%, x = 0.05 and 0.10. X-ray diffractometer (XRD) method was utilized to identify the crystal nature of the obtained powders. The scanning electron microscope (SEM) was exploited to examine the surface topography of the fabricated pellets. X-ray photoelectron spectroscopy (XPS) was employed to find out the valence states of lutetium (Lu) (data is not presented here), iron (Fe), and iridium (Ir). Electrical modulus, dielectric constant, and conductivity of LFO and LFIO ceramics were detailed by dielectric/impedance spectroscopy measurements, which were performed at between − 100 °C (173 K) up to 100 °C (373 K) with 20 °C temperature step. It was exhibited that the undoped LFO has a higher dielectric constant and conductivity than the Ir doped samples. Such a decrement in both dielectric constants and conductivity was related to i) reduction in the ratio of Fe2+ ions and ii) defects and/or distortion in the LFO structure due to Ir substitution.

Pt-based (Zn, Cu) nanodendrites with enhanced catalytic efficiency and durability toward methanol electro-oxidation via trace Ir-doping engineering

Pt-based alloy nanomaterials with nanodendrites (NDs) structures are efficient electrocatalysts for methanol oxidation reaction (MOR), however their durability is greatly limited by the issue of transition metals dissolution. In this work, a facile trace Ir-doping strategy was proposed to fabricate Ir-PtZn and Ir-PtCu alloy NDs catalysts in aqueous medium, which significantly improved the electrocatalytic activity and durability for MOR. The as-prepared Ir-PtZn/Cu NDs catalysts showed distinct dendrites structures with the averaged diameter of 4.1 nm, and trace Ir doping subsequently improved the utilization of Pt atoms and promoted the oxidation efficiency of methanol. The electrochemical characterizations further demonstrated that the obtained Ir-PtZn/Cu NDs possessed enhanced mass activities of nearly 1.23 and 1.28-fold higher than those of undoped PtZn and PtCu, and approximately 2.35 and 2.67-fold higher than that of Pt/C in acid medium. More excitingly, after long-term durability test, the proposed Ir-PtZn and Ir-PtCu NDs still retained about 88.9% and 91.6% of its initial mass activities, which further highlights the key role of Ir-doping in determining catalyst performance. This work suggests that trace Ir-doping engineering could be a promising way to develop advanced electrocatalysts toward MOR for direct methanol fuel cell (DMFC) applications.

Advances in noble metal (Ru, Rh, and Ir) doping for boosting water splitting electrocatalysis

Electrochemical water splitting is promising for producing high-density and green hydrogen, however, the sluggish H2O dissociation process, due to the low H2O adsorption on the catalyst surface, greatly hinders industrial electrochemical water splitting on a large scale.

Methane activation on single-atom Ir-doped metal nanoparticles from first principles.

The breaking of the C-H bond of CH4 is of great importance, and one of the most efficient strategies in heterogeneous catalysis is to alter the electronic structure of a surface by doping it with different metal elements or controlling the stoichiometry. We present an in-depth study on methane activation on pure metal and single-atom Ir-doped alloy nanoparticles, which are constructed based on (100), (110), (111) surfaces using density functional theory (DFT) calculations. DFT results show that the dissociation barriers of CH4 on the Ir-doped alloy surfaces are about 0.3-0.4 eV, much lower than those on the pure metal surfaces (i.e., 0.6-0.8 eV). DFT-based transition state theory further reveals the rates of the first C-H activation on single-atom Ir-doped alloy nanoparticles at the early stages. Importantly, a strong temperature dependence is mainly contributed by the proportion of the exposed (110) surface. The Ir-doped Pt nanoparticle is found to be an efficient catalyst for methane activation in potential industrial applications. These important results are helpful for further designing new metal catalysts for methane activation at the atomic/molecular level.

Dopant-Driven Positive Reinforcement in Ex-Solution Process: New Strategy to Develop Highly Capable and Durable Catalytic Materials.

The ex-solution phenomenon, a central platform for growing metal nanoparticles on the surface of host oxides in real time with high durability and a fine distribution, has recently been applied to various scientific and industrial fields, such as catalysis, sensing, and renewable energy. However, the high-temperature processing required for ex-solutions (>700°C) limits the applicable material compositions and has hindered advances in this technique. Here, an unprecedented approach is reported for low-temperature particle ex-solution on important nanoscale binary oxides. WO3 with a nanosheet structure is selected as the parent oxide, and Ir serves as the active metal species that produces the ex-solved metallic particles. Importantly, Ir doping facilitates a phase transition in the WO3 bulk lattice, which further promotes Ir ex-solution at the oxide surface and eventually enables the formation of Ir particles (<3nm) at temperatures as low as 300°C. Low-temperature ex-solution effectively inhibits the agglomeration of WO3 sheets while maintaining well-dispersed ex-solved particles. Furthermore, the Ir-decorated WO3 sheets show excellent durability and H2 S selectivity when used as sensing materials, suggesting that this is a generalizable synthetic strategy for preparing highly robust heterogeneous catalysts for a variety of applications.

Exploring the morphology, optical and electrical properties of nickel oxide thin films under lead and iridium doping

Expanding the industry and technology of semiconductors requires developing the multifunctionality and performance of p-type transparent conducting oxides (TCO). This work is an attempt to tune the physical properties of nickel oxide (NiO) by using the codoping approach. Pb-doped and (Ir, Pb) codoped films have been deposited by sol-gel combined with spin coating technique. XRD, EDS, and AFM were used to investigate the crystal structure, chemical composition, size, particles' shape, and surface morphology. All films exhibited a polycrystalline structure and a cubic phase. The crystallite size and surface roughness significantly affected by type and dopant content. A maximum root mean square roughness (Rq) with a distinctive island formed layer was obtained at 1.0% Ir + 2.0% Pb doping level. UV–vis-IR measurements showed that the optical parameters; absorption index, optical band gap, refractive index, dielectric constant, and optical conductivity are sensitive to Pb and Ir doping ratios. IV measurements showed good Ohmic behavior and sheet resistance of 13 × 104 Ω/sq. for pure NiO was decreased to be ˂ 6 × 104 Ω/sq., at 2.0% Pb doping. Moreover, the figure of merit exhibited the highest value of 1.35 × 10−7 Ω−1 for NiO: (1.0% Ir + 2.0% Pb) which enables the use of these films as a window layer in smart windows and solar cells and for other optoelectronic applications.

Effect of Zn and Ir doping on microwave absorption of SrFe12-2xZnxIrxO19

With a high anisotropic field, the M-type SrFe12O19 is not considered as a microwave absorber in the frequency range of 0.1–18 GHz. Zn and Ir codoping decreases the anisotropic field greatly. The magnetic resonance frequency falls in the range of 4 GHz − 5.3 GHz in SrFe12-2xZnxIrxO19. Both the permeabilities and the permittivities increase with the increasing Zn and Ir doping as × ≤ 0.5, and decrease in × = 0.7. The different behavior is due to the impurity in × = 0.7. The high permittivity in × = 0.5 are due to the leakage conduction as deduced from the Cole-Cole semicircles, and so is it partly in × = 0.7 as well. Debye relaxations take function in × = 0.1, 0.3 and also 0.7. The impedance matching and the attenuation factor have the best values in × = 0.5. As a result, the × = 0.5 sample has a very good microwave absorbing property with the single-layer bandwidth (RL < −10 dB) as broad as 12.1 GHz at the thickness of 2.1 mm. If the thickness varies from 1.3 mm to 9.5 mm, the bandwidth with RL < −10 dB covers the full frequency range of 1.5–18 GHz. Compared with the advanced materials reported, SrFe12-2xZnxIrxO19 is very competitive as both single-layer and multi-layer absorber. The quarter-wavelength criteria explains the relationship between the optimum thickness and the frequency.

Tiny Ir doping of sub-one-nanometer PtMn nanowires: highly active and stable catalysts for alcohol electrooxidation.

One-dimensional (1D) Pt-based nanowires (NWs) materials serve as efficient catalysts for alcohol electrocatalysis. However, precisely tailoring their size towards sub-one-nanometer scale has been verified as an effective method for enhancing electrocatalytic properties, which is rarely studied. In this work, we developed a one-pot simple yet efficient method for synthesizing a kind of sub-one-nanometer tiny Ir-doped PtMn NWs. The prepared PtMnIr NWs have an ultrathin structure with a mean diameter of around only 0.97 nm (about 3-5 atomic thickness), which display large surface areas and promote superficial Pt atom utilization. With the robust tiny Ir incorporation, the composition-optimized Pt74Mn21Ir5 NWs showed enhanced mass activity, which was 1.51 and 1.53 times higher than those of non-Ir-doped Pt79Mn21 NWs for acidic ethanol oxidation reaction (EOR) and methanol oxidation reaction (MOR). Moreover, benefiting from the atom-level ultrathin size and well-tuned ligand effect from Ir to PtMn, the EOR/MOR mass activities of sub-nanometric Pt74Mn21Ir5 NWs were 3.99- and 3.98-fold higher than those of Pt/C catalysts. More importantly, after successive EOR and MOR CV tests, the Ir-doped PtMn NWs still maintained 85.6% and 73.4% of the initial mass activity, which were much better than those of Pt79Mn21 NWs, Pt NWs, and Pt/C catalysts. This work could be extended to engineering other advanced materials with super sub-one-nanometer structure, which is beneficial for largely improving the catalytic performance.

The impact of Ir doping on the electrical properties of YbFe1−xIrxO3 perovskite-oxide compounds

In this study, YbFe1−xIrxO3 (x = 0, 0.01, 0.10) compounds were synthesized by solid-state reaction method. Chemical and structural analyses of studied compounds were carried out by XPS, SEM and EDX methods. SEM and STEM studies have shown that the particle size shrinks as doping ratio increases. Electrical/dielectric properties of the synthesized compounds were performed in wide-range frequency (1–107 Hz) and temperature (between − 100 and 100 °C with 20 °C steps) using Novocontrol Dielectric/Impedance Spectrometer. Frequency-dependent loss tangent plots exhibited that three dielectric relaxations take place for undoped YbFeO3 (YbFO) compound, whereas two dielectric relaxations were observed for 1 and 10 mol% Ir-doped YbFO compounds. Resistivity measurement revealed that the 1 mol% Ir-substituted YbFO has lower resistivity than undoped.

Atomic and electronic modulation of self-supported nickel-vanadium layered double hydroxide to accelerate water splitting kinetics

Herein, ruthenium (Ru) and iridium (Ir) are introduced to tailor the atomic and electronic structure of self-supported nickel-vanadium (NiV) layered double hydroxide to accelerate water splitting kinetics, and the origin of high hydrogen evolution reaction (HER) and oxygen evolution reaction (OER) activities are analyzed at atomic level. X-ray photoelectron spectroscopy and X-ray absorption near-edge structure spectroscopy studies reveal synergistic electronic interactions among Ni, V, and Ru (Ir) cations. Raman spectra and Fourier and wavelet transform analyses of the extended X-ray absorption fine structure indicate modulated local coordination environments around the Ni and V cations, and the existence of V vacancies. The Debye–Waller factor suggests a severely distorted octahedral V environment caused by the incorporation of Ru and Ir. Theoretical calculations further confirm that Ru or Ir doping could optimize the adsorption energy of intermediates in the Volmer and Heyrovsky steps for HER and accelerate the whole kinetic process for OER.

Identifying valency and occupation sites of Ir dopants in antiferromagnetic α-Fe2O3 thin films with X-ray absorption fine structure and Mössbauer spectroscopy

A combined analysis of Ir-doped α-Fe2O3 (001) films, which show a drastic enhancement in the Morin transition temperature as a result of Ir doping, was performed by employing X-ray absorption near edge structure (XANES), extended X-ray absorption fine structure (EXAFS), and Mössbauer spectroscopy analyses at room temperature. The Mössbauer spectra reveal that the valency of Fe remains 3+ after Ir doping. The XANES spectra indicate that the valency of the Ir ion in Ir-doped α-Fe2O3 varies from 3+ to 4+. The EXAFS analysis results clarified that the Ir ions occupy the Fe-sites of α-Fe2O3. These findings help elucidate the mechanism for controlling the Morin transition temperature in α-Fe2O3 films toward antiferromagnetic spintronic applications.

Enhanced thermoelectric performance in the n-type NbFeSb half-Heusler compound with heavy element Ir doping

The p-type NbFeSb half-Heusler compound has been proved to be a promising thermoelectric (TE) material with a figure of merit zT > 1. However, the corresponding n-type (V,Nb)FeSb solid solutions show poor TE performance. Here, we report the enhanced TE performance of n-type NbFe1-xIrxSb (0.01 < x < 0.08) by band modification and heavy element doping compared with that of the state-of-the-art n-type Co-doped (V,Nb)FeSb. The band effective mass m* b is reduced to 0.76 me, and the high-temperature carrier mobility increases obviously. Debye screening length calculation and model analysis show the additional introduced grain boundary scattering, due to small grain sizes, which deteriorates the room temperature carrier mobility. The heavier doping element Ir not only optimizes the carrier concentration but also introduces strong point defect scattering on phonons, resulting in a minimum thermal conductivity of 3.7 Wm−1K−1 at 1000 K for the NbFe0.92Ir0.02Sb sample. The larger bandgap of NbFeSb effectively suppresses minority carrier excitation. A maximum zT value of 0.5 is obtained at 1000 K for the NbFe0.94Ir0.06Sb sample, almost a 50% increase compared with that of the n-type (V0.6Nb0.4)FeSb samples.

Structural, ultrasonic and spectroscopic studies of tin oxide thin films; effect of Ir and (Ni, Ir) double doping

In this work, tin oxide (SnO2), Sn1−xIrxO2 (0.025 ≤ x ≤ 0.05) and Sn0.95−yIr0.05NiyO2 (0.025 ≤ y ≤ 0.075) thin films were synthesized by a sol-gel spin coating technique. XRD results showed that the films are of polycrystalline rutile structure with crystallite size <31 nm. Raman and FTIR spectra are significantly affected by the type and concentration of dopant atoms. AFM measurements illustrated that the surface of the films have pores of circular shape and both the pores diameter and surface roughness depend on the dopant type. EDS confirmed the substitutional replacement of Sn ions by Ir and Ni in the host lattice. Films densities demonstrate the effect of Ir and Ni on the growth rate. Ultrasonic studies by pulse-echo technique are applied for the first time to investigate the mechanical properties of these films. (Ni, Ir) double doped SnO2 thin films had more pores, less grain agglomeration, less cross-link density and less rigidity. The transmittance spectra and the optical band gap of the films can be tuned by Ir and (Ni, Ir) doping. According to the obtained results, the doped films can be potentially used for different optoelectronic applications as well as for gas sensing.

Enhancement in the interfacial perpendicular magnetic anisotropy and the voltage-controlled magnetic anisotropy by heavy metal doping at the Fe/MgO interface

We investigated the influence of heavy metal doping at the Fe/MgO interface on the interfacial perpendicular magnetic anisotropy (PMA) and the voltage-controlled magnetic anisotropy (VCMA) in magnetic tunnel junctions prepared by sputtering-based deposition. The interfacial PMA was increased by tungsten doping and a maximum intrinsic interfacial PMA energy, Ki,0 of 2.0 mJ/m2 was obtained. Ir doping led to a large increase in the VCMA coefficient by a factor of 4.7 compared with that for the standard Fe/MgO interface. The developed technique provides an effective approach to enhancing the interfacial PMA and VCMA properties in the development of voltage-controlled spintronic devices.

Influence of iridium doping in MgB2 superconducting wires

MgB2 wires with iridium doping were manufactured using the in-situ technique in a composite Cu-Nb sheath. Reaction was performed at 700 °C, 800 °C or 900 °C for 1 h in argon atmosphere. A maximum of about 1.5 at.% Ir replaces Mg in MgB2. The superconducting transition temperature is slightly lowered by Ir doping. The formation of IrMg3 and IrMg4 secondary phase particles is evidenced, especially for a nominal stoichiometry with 2.0 at.% Ir doping. The critical current density and accommodation field of the wires are strongly dependent on the Ir content and are generally weakened in the presence of Ir, although the effect is less pronounced at lower temperatures.