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Pristine and alkaline-earth metal-substituted LaFeO3 (La1−xAxFeO3−δ; x = 0 and 0.2; A = Mg2+, Ca2+, and Sr2+) sintered ceramics are prepared from nanoparticles synthesized via a low-temperature citrate sol–gel technique. X-ray diffraction studies confirm the formation of a phase-pure LaFeO3 structure without any secondary phases for all the La1−xAxFeO3−δ compositions. LaFeO3 and La0.8Mg0.2FeO3−δ ceramics show Raman active modes related to La vibration, oxygen octahedral tilting, bending, and stretching. The optical bandgap is estimated to be 2.34 eV for pure LaFeO3 and reduces to 2.23 eV for La0.8Mg0.2FeO3−δ ceramics. On the contrary, La0.8Ca0.2FeO3−δ and La0.8Sr0.2FeO3−δ ceramics show no features in Raman spectra, consistent with the observation of metallic nature and diffuse band edge without any indication of sharp band edge noted. X-ray absorption spectroscopy (XAS) studies on La-L3 and Fe-K-edges confirm the oxidation states of La3+ and Fe3+ in all these ceramics. Local structural distortions and formation of oxygen vacancies in La0.8A0.2FeO3−δ (A = Mg2+, Ca2+, and Sr2+) ceramics are discerned from XAS structure analysis compared to the pristine LaFeO3 ceramics. Magnetic measurements of La1−xAxFeO3−δ reveal weak ferromagnetic nature except for La0.8Mg0.2FeO3−δ, which shows a large magnetization of 4.6 (6.7) emu/g at 300 (5) K. The ferromagnetic behavior of La0.8Mg0.2FeO3−δ ceramics seems to originate from the modification of hybridization between Fe(3d)–O(2p), La(5d)–O(2p), and Fe(4sp)–O(2p) orbitals. An anomalous magnetic transition observed only in zero-field-cooled curves at 88 K in La0.8Ca0.2FeO3−δ and La0.8Sr0.2FeO3−δ ceramics is correlated to the formation of new electronic states containing O 2p character as discerned from pre-peak O-K-edge. [ABSTRACT FROM AUTHOR]

Lithium-ion batteries suffer from reduced capacities and stabilities at low temperature due to poor Li intercalation to the graphite anode. Graphite has a high activation energy (∼0.6 eV) to accommodate Li ions, resulting in a substantial capacity drop at low temperatures. Additionally, it can induce the formation of Li dendrites on the surface of graphite. To address this issue, we designed and synthesized a redox-active fluorothianthrene-based MOF (SKIER-5). SKIER-5, which undergoes three-electron redox reactions resulting from the fluorothianthrene-based organic ligand and Ni, exhibited excellent electrochemical performance at various temperatures when used as an anode. In particular, the discharge capacities of SKIER-5 were significantly higher than those of commercial graphite at low temperatures (<−10 °C) because of the lower activation energy (∼0.23 eV) for charge transfer. Moreover, it maintained stability when cycled at −20 °C, highlighting its potential as a promising anode material in low-temperature environments. [ABSTRACT FROM AUTHOR]

Delafossite CuCrO2 (CCO), CuCr0.96V0.04O2 (CCVO) thin films were successfully prepared on Si (100) substrates, using the pulsed laser deposition technique. The effect of doping was studied using x-ray diffraction (XRD), x-ray absorption spectroscopy (XAS), temperature-dependent resistivity measurements, and I–V characteristics. The XRD results confirmed the single-phase rhombohedral structure of the prepared thin films, and the XAS results conveyed the mixed Cu+ and Cu2+ ions in the CCVO and CCO samples. The valence state of Cr was unaltered under the doping effects and remained + 3 (i.e., Cr+3). The modified hybridization of the O 2p orbitals with the metal d (V, Cr,) orbitals was confirmed in the O K-edge spectra. Insertion of V5+ ions in the CCO lattice introduced an electron doping effect. Thus, the basic p-type character of CCO was affected by the V doping and, therefore, increases in the resistivity or decreases in the p-type character were observed in the I–V measurements. From this study; the method of selective mono-doping can be a useful tool to tailor the bandgap and the type of conductivity in other delafossite semiconductors. [ABSTRACT FROM AUTHOR]

Distribution of Zn 2 + , Al 3 + , and Fe 3 + ions on tetrahedral and octahedral sites in Fe 3 + -doped ZnAl 2 O 4 nanocrystals is studied through detailed x-ray diffraction (XRD) analysis. Significant changes in the intensity ratio of (220), (311), (400), and (422) diffraction peaks upon Fe addition were perceived, whose correlation with lattice inversion, Fe 3 + ions distribution, and ionic vacancies is probed through simulations and Rietveld refinement. Fe 3 + ions were found to be occupying tetrahedral sites in increasing proportion with the doping concentration, leading to decreased spinel inversion. However, different orders of defects, viz., cation and anion vacancies were also found to be playing their part in the statistical distribution of cations on octahedral/tetrahedral interstices. Fe L 2 , 3 -edge x-ray absorption near edge structure spectroscopy indicated Fe 3 + ions being present on tetrahedral as well octahedral interstices and distortion in cation polyhedra, while O K-edge inferred formation of different orders of ionic vacancies upon Fe addition, thereby corroborating the results from XRD. The photoluminescence study illustrated the quenched emission intensity upon Fe doping, with almost no change in emission color, and signatures of tetrahedral/octahedral Fe 3 + occupancy in the lattice. Thus, this study highlights the variation in degrees of freedom associated with atomic arrangements in spinel ZnAl 2 O 4 lattice upon Fe 3 + addition. [ABSTRACT FROM AUTHOR]

Solar fuel production by photosynthetic systems strongly relies on developing efficient and stable oxygen-evolution catalysts (OECs). Cerium(IV) ammonium nitrate (CAN) has been the most commonly used sacrificial oxidant to investigate OECs. Although many metal oxides have been extensively investigated as OECs in the presence of CAN, mechanistic studies were rarely reported. Herein, first, Fe(III) (hydr)oxide (FeOxHy) was prepared by the reaction of Fe(ClO4)3 and KOH solution and characterized by some methods. Then, changes in Fe oxide in the presence of CAN during the OER were tracked using in situ Raman spectroscopy, in situ X-ray absorption spectroscopy, in situ visible spectroscopy, and in situ electron paramagnetic resonance spectroscopy. FeOxHy in the presence of CAN and during the OER converted to γ-Fe2O3 and [Fe(H2O)6]3+, and a small amount of oxygen was formed. A maximum turnover frequency and turnover number of 10−6 s−1 and 1.3 × 10−3 mol(O2)/mol(Fe) (for half an hour) in the presence of CAN (0.20 M) and FeOxHy were observed. [ABSTRACT FROM AUTHOR]

ZnO is a potential candidate for providing an economic and environmentally friendly substitute for energy storage materials. Therefore, in this work, Fe-doped ZnO nanostructures prepared using the microwave irradiation procedure were investigated for structural, morphological, magnetic, electronic structural, specific surface area and electrochemical properties to be used as electrodes for supercapacitors. The X-ray diffraction, high-resolution transmission electron microscopy images, and selective-area electron diffraction pattern indicated that the nanocrystalline structures of Fe-doped ZnO were found to possess a hexagonal wurtzite structure. The effect of Fe doping in the ZnO matrix was observed on the lattice parameters, which were found to increase with the dopant concentration. Rods and a nanosheet-like morphology were observed via FESEM images. The ferromagnetic nature of samples is associated with the presence of bound magnetic polarons. The enhancement of saturation magnetization was observed due to Fe doping up to 3% in correspondence with the increase in the number of bound magnetic polarons with an Fe content of up to 3%. This behavior is observed as a result of the change in the oxidation state from +2 to +3, which was a consequence of Fe doping ranging from 3% to 5%. The electrode performance of Fe-doped ZnO nanostructures was studied using electrochemical measurements. The cyclic voltammetry (CV) results inferred that the specific capacitance increased with Fe doping and displayed a high specific capacitance of 286 F·g−1 at 10 mV/s for 3% Fe-doped ZnO nanostructures and decreased beyond that. Furthermore, the stability of the Zn0.97Fe0.03O electrode, which was examined by performing 2000 cycles, showed excellent cyclic stability (85.0% of value retained up to 2000 cycles) with the highest specific capacitance of 276.4 F·g−1, signifying its appropriateness as an electrode for energy storage applications. [ABSTRACT FROM AUTHOR]

The electrochemical fixation of carbon dioxide (CO2) into organic halides is one of the most prominent strategies for mitigating atmospheric CO2 emission, along with the difficulties associated with the toxic and carcinogenic halogenated compounds. Cu-based nanomaterials have been explored for numerous applications in nanotechnology, including electrocatalysis, organic catalytic transformations, and photocatalysis. In this work, we have designed and developed a Cu-embedded carbazole-derived porous organic polymer (Cu@Cz-POP) nanohybrid by utilizing the Friedel–Crafts alkylation approach and employing 1,4-dimethoxybenzene as the cross-linking agent comprising unique characteristic features of the extended π-conjugated system along with an active metal center with tunable electrochemical properties. The Brunauer–Emmett–Teller surface area of the conjugated Cz-POP is found to be 1060 m2 g–1. The X-ray photoelectron spectroscopy (XPS) study demonstrates the formation of CuO nanoparticles in the polymeric framework. X-ray absorption fine structure analysis (EXAFS) also reveals the existence of CuO with a smaller fraction of Cu in the polymeric framework, which is corroborated with the XPS analysis. The Cu@Cz-POP nanohybrid is fabricated by drop-casting over a Ni foam, showing promising electrocatalytic activity toward electrocarboxylation of benzyl bromide in 0.1 M TBA·BF4/CH3CN with saturated CO2 medium with a current density of 120 mA cm–2 delivering 65% yield of phenylacetic acid (PAA) as the primary product along with traces of benzyl 2-phenylacetate (BPA) and 1,2-diphenylethane (DPE), and the turnover frequency is found to be 8.556 × 10–7 s–1. Density functional theory calculations demonstrate that CuO is adsorbed more favorably at the N1 nitrogen atom of Cz-POP. An electron transfer from the N1 atom and the aromatic rings of Cz-POP to the CuO center is observed and confirmed by the overlap of alpha orbitals. [ABSTRACT FROM AUTHOR]

Herein, we have reported a novel strategy for improving the electrochemical performance of laser-induced graphene (LIG) supercapacitors (SCs). The LIG was prepared using a CO2 laser system. The polyimide polymer was the source material for the fabrication of the LIG. The doping process was performed in situ using the CO2 laser, which works as a rapid thermal treatment to combine graphene and NiO particles. NiO was used to improve the capacitance of graphene by combining an electric double-layer capacitor (EDLC) with the pseudo-capacitance effect. The high-resolution transmission electron microscopy, energy-dispersive X-ray spectroscopy, and Raman spectroscopy showed that the structure of the LIG is multilayered and waved. The HRTEM image proves the distribution of NiO fine particles with sizes of 5–10 nm into the graphene layers. The electrochemical performance of the as-prepared LIG was tested. The effect of the combination of the two materials (oxide and carbon) was investigated at different concentrations. The LIG showed a specific capacitance of 69 Fg−1, which increased up to 174 Fg−1 for the NiO-doped LIG. The stability investigations showed that the electrodes were very stable for more than 1000 cycles. This current study establishes an innovative method to improve the electrochemical properties of LIG. [ABSTRACT FROM AUTHOR]

This study explores influence of charge transfer and X-ray absorption characteristics in aluminum (Al) and copper (Cu) co-doped zinc oxide (ZnO) nanostructures for perovskite solar cell electrodes. Sol-gel technique was employed to synthesize the nanostructures, and their optical and morphological properties were investigated. X-ray diffraction (XRD) analysis confirmed high crystallinity and also single-phase composition of all the samples, particularly up to 5% Al co-doping. Field emission scanning electron microscopy (FESEM) exhibited the formation of pseudo-hexagonal wurtzite nanostructure and the transition to nanorods at 5% Al co-doping. Diffuse reflectance spectroscopy indicated a reduction in the optical band gap of co-doped zinc oxide from 3.11 to 2.9 eV with increasing Al doping. Photoluminescence spectra (PL) exhibited a decrease in peak intensity, suggesting enhanced conductivity in ZnO, also confirmed from I-V measurements. Near-edge X-ray absorption fine structure (NEXAFS) analysis depicts that charge transfer from Al to oxygen (O) species enhanced the photosensing properties of the nanostructure, which was supported by FESEM micrographs and PL spectra. Furthermore, the study discovered that 5% Al co-doping significantly reduced the density of emission defects (deep-level) in Cu–ZnO nanostructure. These findings highlight the potential of Cu and Al co-doped ZnO materials for perovskite solar cell electrodes, as their improved optical and morphological properties resulting from charge transfer could enhance device performance. The investigation of charge transfer and X-ray absorption characteristics provides valuable insights into the underlying mechanisms and behaviors of the co-doped ZnO nanostructures. However, further research is required to delve into the intricate hybridization resulting from charge transfer and explore the broader impact of co-doping on other properties of the nanostructures, enabling a comprehensive understanding of their potential applications in perovskite solar cells. [ABSTRACT FROM AUTHOR]

Magnetic nanoparticles of NiFe2O4 were successfully prepared by utilizing the sol–gel techniques. The prepared samples were investigated through various techniques such as X-ray diffraction (XRD), transmission electron microscopy (TEM), dielectric spectroscopy, DC magnetization and electrochemical measurements. XRD data analysed using Rietveld refinement procedure inferred that NiFe2O4 nanoparticles displayed a single-phase nature with face-centred cubic crystallinity with space group Fd-3m. Average crystallite size estimated using the XRD patterns was observed to be ~10 nm. The ring pattern observed in the selected area electron diffraction pattern (SAED) also confirmed the single-phase formation in NiFe2O4 nanoparticles. TEM micrographs confirmed the uniformly distributed nanoparticles with spherical shape and an average particle size of 9.7 nm. Raman spectroscopy showed characteristic bands corresponding to NiFe2O4 with a shift of the A1g mode, which may be due to possible development of oxygen vacancies. Dielectric constant, measured at different temperatures, increased with temperature and decreased with increase in frequency at all temperatures. The Havrilliak–Negami model used to study the dielectric spectroscopy indicated that a NiFe2O4 nanoparticles display non-Debye type relaxation. Jonscher's power law was utilized for the calculation of the exponent and DC conductivity. The exponent values clearly demonstrated the non-ohmic behaviour of NiFe2O4 nanoparticles. The dielectric constant of the nanoparticles was found to be >300, showing a normal dispersive behaviour. AC conductivity showed an increase with the rise in temperature with the highest value of 3.4 × 10−9 S/cm at 323 K. The M-H curves revealed the ferromagnetic behaviour of a NiFe2O4 nanoparticle. The ZFC and FC studies suggested a blocking temperature of ~64 K. The saturation of magnetization determined using the law of approach to saturation was ~61.4 emu/g at 10 K, corresponding to the magnetic anisotropy ~2.9 × 104 erg/cm3. Electrochemical studies showed that a specific capacitance of ~600 F g−1 was observed from the cyclic voltammetry and galvanostatic charge–discharge, which suggested its utilization as a potential electrode for supercapacitor applications. [ABSTRACT FROM AUTHOR]

To meet the growing demand for efficient and sustainable power sources, it is crucial to develop high-performance energy storage systems. Additionally, they should be cost-effective and able to operate without any detrimental environmental side effects. In this study, rice husk-activated carbon (RHAC), which is known for its abundance, low cost, and excellent electrochemical performance, was combined with MnFe2O4 nanostructures to improve the overall capacitance of asymmetric supercapacitors (ASCs) and their energy density. A series of activation and carbonization steps are involved in the fabrication process for RHAC from rice husk. Furthermore, the BET surface area for RHAC was determined to be 980 m2 g−1 and superior porosities (average pore diameter of 7.2 nm) provide abundant active sites for charge storage. Additionally, MnFe2O4 nanostructures were effective pseudocapacitive electrode materials due to their combined Faradic and non-Faradic capacitances. In order to assess the electrochemical performance of ASCs extensively, several characterization techniques were employed, including galvanostatic charge –discharge, cyclic voltammetry, and electrochemical impedance spectroscopy. Comparatively, the ASC demonstrated a maximum specific capacitance of ~420 F/g at a current density of 0.5 A/g. The as-fabricated ASC possesses remarkable electrochemical characteristics, including high specific capacitance, superior rate capability, and long-term cycle stability. The developed asymmetric configuration retained 98% of its capacitance even after 12,000 cycles performed at a current density of 6A/g, demonstrating its stability and reliability for supercapacitors. The present study demonstrates the potential of synergistic combinations of RHAC and MnFe2O4 nanostructures in improving supercapacitor performance, as well as providing a sustainable method of using agricultural waste for energy storage. [ABSTRACT FROM AUTHOR]

Oxygen evolution reaction (OER) under acidic conditions becomes of significant importance for the practical use of a proton exchange membrane (PEM) water electrolyzer. In particular, maximizing the mass activity of iridium (Ir) is one of the maiden issues. Herein, the authors discover that the Ir‐doped calcium copper titanate (CaCu₃Ti₄O₁₂, CCTO) perovskite exhibits ultrahigh mass activity up to 1000 A gIr−1 for the acidic OER, which is 66 times higher than that of the benchmark catalyst, IrO2. By substituting Ti with Ir in CCTO, metal‐oxygen (M‐O) covalency can be significantly increased leading to the reduced energy barrier for charge transfer. Further, highly polarizable CCTO perovskite referred to as "colossal dielectric", possesses low defect formation energy for oxygen vacancy inducing a high number of oxygen vacancies in Ir‐doped CCTO (Ir‐CCTO). Electron transfer occurs from the oxygen vacancies and Ti to the substituted Ir consequentially resulting in the electron‐rich Ir and ‐deficient Ti sites. Thus, favorable adsorptions of oxygen intermediates can take place at Ti sites while the Ir ensures efficient charge supplies during OER, taking a top position of the volcano plot. Simultaneously, the introduced Ir dopants form nanoclusters at the surface of Ir‐CCTO, which can boost catalytic activity for the acidic OER. [ABSTRACT FROM AUTHOR]

Generation of hydrogen fuel via electrochemical water splitting powered by sustainable energy, such as wind or solar energy, is an attractive path toward the future renewable energy landscape. However, current water electrolysis requires desalinated water resources, eventually leading to energy costs and water scarcity. The development of cost‐effective electrocatalysts capable of splitting saline water feeds directly can be an evident solution. Herein, a surface reconstructed nickel‐iron layered double hydroxide (NF‐LDH) is reported as an exceptionally active and durable bifunctional electrocatalyst for saline water splitting without chloride corrosion. The surface reconstructed NF‐LDH consists of Ni3Fe alloy phase interconnected in a 2D network in which an ultrathin (≈2 nm) and low‐crystalline NiFe (oxy)hydroxide phase are formed on the surface. The NiFe (oxy)hydroxide phase draws large anodic current densities, satisfying the level of practical application, while the Ni3Fe alloy phase is simultaneously responsible for the high catalytic activity for cathodic reactions and superior corrosion resistance. The surface reconstructed NF‐LDH electrode can be easily fabricated in a large electrode area (up to 25 cm2) and can successfully produce hydrogen fuels from saline water powered by the laboratory‐made low‐intensity photovoltaic cell. [ABSTRACT FROM AUTHOR]

Herein, we reported the effect of thermal annealing on the ZnFe2O4 film and substrate/film interface. These films were grown on MgO(200) substrate using radio frequency sputtering and were further annealed at 200, 400, and 600 °C. The thickness of the as-grown film was 109 nm, which was observed to decrease with annealing due to the increase of film/substrate interface as determined from high-resolution electron microscopy (HRTEM). Zn K-edge X-ray absorption near edge structure (XANES) spectrum exhibits spectral features at 600 °C that are characteristics of ZnFe2O4. Annealing modulated the metal–oxygen hybridization process in these films as evidenced from the pre-edge region of O K-edge spectra. Selected area diffraction further envisages changes in the crystalline nature of films and interface regions. [ABSTRACT FROM AUTHOR]

The exploding electric‐vehicle market requires cost‐effective high‐energy materials for rechargeable lithium batteries. The manganese‐rich spinel oxide LiNi0.5Mn1.5O4 (LNMO) can store a capacity greater than 200 mAh g−1 based on the multi‐cation (Ni2+/Ni4+ and Mn3+/Mn4+) redox centers. However, its practical capacity is limited to Ni2+/Ni4+ redox (135 mAh g−1) due to the poor reversibility of Mn3+/Mn4+ redox. This instability is generally attributed to the Jahn–Teller distortion of Mn3+ and its disproportionation, which leads to severe Mn dissolution. Herein, for the first time, the excellent reversibility of Mn3+/Mn4+ redox within 2.3–4.3 V is demonstrated, requiring revisiting the previous theory. LNMO loses capacity only within a wide voltage range of 2.3–4.9 V. It is revealed that a dynamic evolution of the electrochemical interface, for example, potential‐driven rocksalt phase formation and decomposition, repeatedly occurs during cycling. The interfacial evolution induces electrolyte degradation and surface passivation, impeding the charge‐transfer reactions. It is further demonstrated that stabilizing the interface by electrolyte modification extends the cycle life of LNMO while using the multi‐cation redox, enabling 71.5% capacity retention of LNMO after 500 cycles. The unveiled dynamic oxide interface will propose a new guideline for developing Mn‐rich cathodes by realizing the reversible Mn redox. [ABSTRACT FROM AUTHOR]

We present an extensive review of different techniques, such as x-ray magnetic circular dichroism, Mössbauer spectroscopy, and x-ray absorption spectroscopy, for determining the cation distribution in ferrites, and a comparison between these techniques is established. We describe the basic principles of these techniques to find the cation occupancies and highlight the important results obtained from these measurements on ferrite nanoparticles and thin films. Cation distribution, an important characteristic that controls the structural, electrical, and magnetic properties of ferrites, is strongly affected by the synthesis methods. Therefore, various synthesis techniques are reported for preparing ferrite nanoparticles and thin films. A summary correlating these techniques and the cation distribution in ferrite nanoparticles and thin films is presented. [ABSTRACT FROM AUTHOR]

The electrochemical nitrate reduction reaction (eNO3RRs) can produce value-added chemicals such as ammonia (NH3) via multiple steps. Here, we demonstrate that bimetallic Cu–Pd–Ox alloy electrocatalysts can promote selective NH3 production from the eNO3RR, especially at low overpotential, by accelerating the rate-determining hydrogenation of NO2−, a critical intermediate, on the Cu catalyst. The synergistic effect of Cu and Pd affords 14 times higher NH3 yield (1.41 mg h−1 cm−2) at −0.2 VRHE with an optimum composition (Cu0.65Pd0.35Ox) than that obtained using bare CuOx. The operando near edge X-ray absorption fine structure (NEXAFS) and simulation results support that the high hydrogen affinity of Pd facilitates sequential hydrogenation on metallic Cu active sites, consequently increasing the NH3 selectivity and production rate. Our study sheds light on the mechanism of the catalytic eNO3RR and presents a design strategy for more advanced eNO3RR electrocatalysts. [ABSTRACT FROM AUTHOR]

Correction for 'Redox-active conductive metal–organic framework with high lithium capacities at low temperatures' by Yogendra Kumar et al., J. Mater. Chem. A, 2024, https://doi.org/10.1039/D4TA01779J. [ABSTRACT FROM AUTHOR]

N‐coordinated Ni single atom (Ni–NC) is one of the best catalysts for the CO2 reduction reaction (CO2RR) to produce CO. However, no bulk Ni materials have exhibited high catalytic activity for CO2RR. Herein, it is shown that NiS nanoparticles mimicking the electronic structure of Ni–NC in real‐time enhance the CO2RR activity in a zero‐gap electrolyzer. In situ/Operando X‐ray absorption spectroscopy suggests that under a cathodic potential, the electronic structure of NiS changes similarly to that of Ni–NC and modulated Ox–zSy ligands with similar properties to Ni ligands, resulting in a mimicked electronic structure. However, NiS exhibits low stability owing to the loss of S species, key to mimicking N ligands. The future challenges in finding a stable mimicked electronic structure are discussed. Moreover, this work provides new insights into the development of catalysts from materials that have not generally been considered previously. [ABSTRACT FROM AUTHOR]

In the context of energy storage, the oxygen-evolution reaction (OER, 2H2O → O2 + 4H+ + 4e−) through the water-oxidation reaction is a thermodynamically uphill reaction in overall water splitting. In recent years, copper(II) coordination compounds have been extensively used for the OER. However, challenges remain in finding the mechanism of the OER in the presence of these metal coordination compounds. Herein, the electrochemical OER activity is investigated in the presence of a copper(II) coordination compound at pH ≈ 7. While the investigations on finding true catalysts for the OER are focused on the working electrode, herein, for the first time, the focus is on the decomposition of copper(II) coordination compound (CuL3, L: 2,2′-bipyridine N,N′-dioxide) during the OER on the counter electrode toward the precipitation of copper(I) oxide and metallic Cu. [ABSTRACT FROM AUTHOR]

Nanocrystals of GaFeO3 were prepared using co-precipitation followed by thermal annealing at 800 °C for 6 h. The lattice parameters and crystallite size were studied using x-ray diffraction (XRD). Transmission electron microscopy (TEM) measurements were performed to study the size and morphology and revealed the formation of 40–70 nm sized nanoparticles. X-ray absorption near-edge structure measurement was performed to probe the valence state of constituent elements in the GaFeO3 nanocrystals. It has been observed that Fe is present in solely the +3 valence state (i.e., Fe3+). The Ga3+ ions are found with vivid distribution at tetrahedral and octahedral sites and the occupancy of Ga3+ ions is quantitatively evaluated using Ga K-edge XANES spectra. The low-temperature (50 K) M-H loop measurement conveys a ferrimagnetic character of GaFeO3 compound. The paramagnetic behavior is seen at 300 K. The observed magnetic moments per formula unit (~ 1.6 μB) are close to the magnetic moment of Fe3+ ions with a low spin state (t2g5). The abundant Ga3+ ions at the tetrahedral site, as confirmed by Ga K-edge XANES analysis, lead to weak anisotropy in the compound and favor the regular hysteresis loop rather the pinched-like hysteresis loop at 50 K. [ABSTRACT FROM AUTHOR]

BiFe1−xCrxO3, (0 ≤ x ≤ 10) nanoparticles were prepared through the sol–gel technique. The synthesized nanoparticles were characterized using various techniques, viz., X-ray diffraction, high-resolution field emission scanning electron microscopy (HRFESEM), energy dispersive spectroscopy (EDS), UV–Vis absorption spectroscopy, photoluminescence (PL), dc magnetization, near-edge X-ray absorption spectroscopy (NEXAFS) and cyclic voltammetry (CV) measurements, to investigate the structural, morphological, optical, magnetic and electrochemical properties. The structural analysis showed the formation of BiFeO3 with rhombohedral (R3c) as the primary phase and Bi25FeO39 as the secondary phase. The secondary phase percentage was found to reduce with increasing Cr content, along with reductions in crystallite sizes, lattice parameters and enhancement in strain. Nearly spherical shape morphology was observed via HRFESEM with Bi, Fe, Cr and O as the major contributing elements. The bandgap reduced from 1.91 to 1.74 eV with the increase in Cr concentration, and PL spectra revealed emissions in violet, blue and green regions. The investigation of magnetic field (H)-dependent magnetization (M) indicated a significant effect of Cr substitution on the magnetic properties of the nanoparticles. The ferromagnetic character of the samples was found to increase with the increase in the Cr concentration and the increase in the saturation magnetization. The Fe (+3/+4) was dissolved in mixed-valence states, as found through NEXAFS analysis. Electrochemical studies showed that 5%-Cr-doped BFO electrode demonstrated outstanding performance for supercapacitors through a specific capacitance of 421 F g−1 measured with a scan rate of 10 mV s−1. It also demonstrated remarkable cyclic stability through capacitance retention of >78% for 2000 cycles. [ABSTRACT FROM AUTHOR]

Carrier dynamics affects photocatalytic systems, but direct and real-time observations in an element-specific and energy-level-specific manner are challenging. In this study, we demonstrate that the dynamics of photo-generated holes in metal oxides can be directly probed by using femtosecond X-ray absorption spectroscopy at an X-ray free-electron laser. We identify the energy level and life time of holes with a long life time (230 pico-seconds) in nano-crystal materials. We also observe that trapped holes show an energy distribution in the bandgap region with a formation time of 0.3 pico-seconds and a decay time of 8.0 pico-seconds at room temperature. We corroborate the dynamics of the electrons by using X-ray absorption spectroscopy at the metal L-edges in a consistent explanation with that of the holes. Direct and real-time observation of the excess holes in an element-specific and energylevel-specific manner is a challenging task. Here the authors present a complete hole dynamics of photo-excited anatase TiO2 with 100 femto-second resolution. [ABSTRACT FROM AUTHOR]

We synthesized Cu-doped Mg2B2O5 nanophosphors using a combustion method, and investigated their structural, morphological, optical band gap, electronic structure, and photo/thermo-luminescence properties using x-ray diffraction (XRD), selected area electron diffraction (SAED), high-resolution transmission electron microscopy (HR-TEM), diffuse reflectance spectroscopy (DRS), x-ray absorption near-edge structure (XANES) spectroscopy, photoluminescence (PL) spectroscopy, and thermoluminescence (TL) glow curves. Rietveld refinements of the XRD patterns confirmed the formation of single triclinic phase (space group P-1) for the pure and doped Mg2B2O5 nanophosphors. Variations in the cell parameters as a function of dopant concentrations has been determined. The HR-TEM images confirmed the formation of aggregated particles of unusual morphology. The SAED pattern also confirmed the triclinic phase in Cu-doped Mg2B2O5 nanophosphors. The band gap of the Cu-doped samples decreased from 5.18 eV to 5.10 eV. The XANES study at the Cu L-edge confirmed the Cu2+ ions in the Cu-doped Mg2B2O5 nanophosphors. The O K-edge spectrum of pure Mg2B2O5 confirmed the existence of marginal oxygen vacancies in the sample, which increases after Cu incorporation in the Mg2B2O5 nanophosphors. Peak position variation in the O K-edge confirmed the modified hybridization among the O 1s to O 2p transitions. From the PL studies and CIE chromaticity diagram, a yellow-reddish color emission from the Cu-doped Mg2B2O5 was observed. The TL glow curves obtained after gamma irradiation of the samples were used to evaluate the order of kinetics, activation energy, and frequency factor. The present results infer that Cu-doped magnesium pyroborate could be a potential candidate for solid-state lighting and radiation dosimetry-based applications. [ABSTRACT FROM AUTHOR]

SrVO3 films have been deposited on quartz substrates using radiofrequency (RF) sputtering technique. Ag− ions have been implanted with three fluences: 1 × 1015 ions/cm2, 3 × 1015 ions/cm2, and 5 × 1015 ions/cm2. The glancing-angle x-ray diffraction (GIXRD) results exhibited a decrease in the peak intensity; however, the results ruled out the possibility of other secondary phase formation upon increasing the Ag− ion fluence. Field emission scanning electron microscopy (FESEM) results revealed that Ag implantation has sputtered the surface layer and created rough/emptied films. Significant broadening/splitting of V L2 near-edge x-ray absorption fine structure (NEXAFS) spectra convey the incorporation of Ag 4d states in the energy band structure of SrVO3 and electronic transitions from V 2p1/2 states to the Ag-related states. O K-edge spectra have ruled out the charge transfer of O 1s orbits to the Ag states, even upon increasing the Ag concentration, and nullified the formation of AgO types of secondary phases. [ABSTRACT FROM AUTHOR]

Computational calculations and experimental studies reveal that the CoOOH phase and the intermediate-spin (IS) state are the key factors for realizing efficient Co-based electrocatalysts for the oxygen evolution reaction (OER). However, according to thermodynamics, general cobalt oxide converts to the CoO2 phase under OER condition, retarding the OER kinetics. Herein, we demonstrate a simple and scalable strategy to fabricate electrodes with maintaining Fe-CoOOH phase and an IS state under the OER. The changes of phase and spin states were uncovered by combining in-situ/operando X-ray based absorption spectroscopy and Raman spectroscopy. Electrochemical reconstruction of chalcogenide treated Co foam affords a highly enlarged active surface that conferred excellent catalytic activity and stability in a large-scale water electrolyzer. Our findings are meaningful in that the calculated results were experimentally verified through the operando analyses. It also proposes a new strategy for electrode fabrication and confirms the importance of real active phases and spin states under a particular reaction condition. The phase and spin state affect catalytic activity of Co-based catalysts for oxygen evolution reaction. Herein, the authors demonstrate a simple reconstruction strategy to fabricate electrodes maintaining a Fe-CoOOH phase and an intermediate-spin state during catalysis. [ABSTRACT FROM AUTHOR]

A cobalt coordination compound with azo-ligand linkers combined with linked bisulfonate moieties has been argued to be an efficient catalyst for the oxygen-evolution reaction (OER) (H.-T. Shi, X.-X. Li, F.-H. Wu and W.-B. Yu, Dalton Trans., 2017, 46, 16321.). In the previously published report, this cobalt compound (compound 1) was believed to display a high turnover frequency (5 s−1) at η = 720 mV at pH 9. Herein, the OER in the presence of compound 1 is reinvestigated. The nanosized oxide-based particles formed after the OER in the presence of compound 1 were tracked by electrochemical methods, scanning electron microscopy (SEM), energy dispersive spectrometry (EDX), X-ray diffraction studies (XRD), (High-resolution) transmission electron microscopy ((HR)TEM), Raman spectroscopy, X-ray absorption spectroscopy (XAS), and X-ray photoelectron spectroscopy (XPS). Based on these experiments, it is proposed that a candidate for the true catalyst of the OER in the presence of compound 1 is cobalt oxide. During the OER and using chronoamperometry, the oxidation state of Co ions for the formed Co oxide is (III), but after consecutive CVs the oxidation states of Co ions for the formed Co oxide are (II) and (III). The results shed new light on the role of Co oxide nanoparticles formed in the presence of this Co coordination compound during the OER. Our experimental data also show that for the OER in the presence of a homogeneous (pre)catalyst, careful analyses to find the role of metal oxides are necessary for informed progress. The present findings also might help to find the mechanism of the OER in the presence of coordination compounds. [ABSTRACT FROM AUTHOR]

Development of an efficient and stable electrocatalyst for the oxygen evolution reaction (OER) is crucial to generate hydrogen via water splitting as a sustainable fuel. Nickel iron layered double hydroxides (NF-LDHs) are considered the most promising electrocatalysts for alkaline water oxidation among various low-cost transition metal-based electrocatalysts although exact mechanisms are still on debate. Herein, we disclose that quaternary multimetallic Ni–Fe–Al–Co LDHs (NFAC-MELDHs) function as one of the best catalysts for alkaline as well as seawater oxidation due to the synergetic effects among the four different redox-flexible metals. The multimetallic Ni–Fe–Al–Co LDHs are prepared via the metal–organic framework (MOF)-derived electrochemical incorporation of fourth transition metal (Co) into ternary Ni–Fe–Al LDHs grown by a hydrothermal reaction. Moreover, we reveal an exact electrocatalytic mechanism for the OER in NFAC-MELDHs via ex situ spectroscopies in combination with density functional theory (DFT) calculations. Redox-flexible Fe is identified with a real active site in synergy with the neighboring metals stabilizing adsorption of oxygen intermediates and simultaneously facilitating charge transfer. In consequence, NFAC-MELDHs exhibit one of the lowest overpotentials of 220 and 280 mV for affording a current density of 100 mA cm−2 in alkaline and simulating seawater solutions, respectively. More importantly, activity and stability merits in electrocatalysis for the OER are improved in the sequence of unary, binary, ternary, and quaternary LDHs, implying that catalyst design using multimetals for LDHs is a highly promising strategy. [ABSTRACT FROM AUTHOR]

A magnetic vanadium oxide nanoparticles supported on spinel copper ferrite (CuFe2O4–VOx) are prepared, characterized, and examined for the peroxymonosulfate (PMS) activation to degrade Rhodamine B (RhB) in water solution. Interestingly, the results show that despite the inability of mixture of copper ferrite and vanadium oxides nanoparticles to the effective RhB decomposition, the prepared catalyst exhibits an excellent catalytic ability toward RhB oxidation. The influence of vital parameters, such as temperature, PMS concentration, catalyst loading, and initial pH are discussed comprehensively. The kinetic studies demonstrate that the pseudo‐first‐order model is well fitted for RhB degradation in CuFe2O4–VOx/PMS system and the activation energy is estimated at 19.60 kJ mol−1. Furthermore, it is found out that the concentration of leached metal ions in solution is negligible and PMS activation is done mainly on the surface of the catalyst. A probable mechanism of PMS activation over RhB degradation is proposed based on the results of free radical quenching studies and X‐ray photoelectron spectroscopy (XPS) analysis. Radical quenching experiments using various scavengers suggest SO4•− as a main reactive species in the degradation. [ABSTRACT FROM AUTHOR]

Applicability of spinel compounds is mainly governed by cation distribution in them. In the presented study, thermally induced cation ordering is found to influence the emission color of Mg 2 + , Fe 3 + co-doped ZnAl 2 O 4 spinel. Cation distribution is monitored through Mg K-edge, Fe L 2 , 3 -edge, O K-edge X-ray absorption near edge structure spectroscopy and X-ray diffraction analysis using synchrotron radiation. Thermal treatment provided sufficient energy to Zn 2 + , Mg 2 + , Al 3 + and Fe 3 + cations to redistribute themselves on tetrahedral and octahedral sites, and reduce the octahedral distortion, thereby gaining stability. Reduced inversion accompanied by decrease in oxygen vacancies, while increase in tetrahedral and octahedral site vacancies contributed toward more intense blue emission band and quenched yellow band, changing the emission color from bluish-white to blue. Correlation derived between cation ordering and luminescence upon thermal treatment predict Mg 2 + , Fe 3 + co-doped ZnAl 2 O 4 nanophosphors to be useful in thermal sensing applications. [ABSTRACT FROM AUTHOR]

The voltage reversal of water electrolyzers and fuel cells induces a large positive potential on the hydrogen electrodes, followed by severe system degradation. Applying a reversible multifunctional electrocatalyst to the hydrogen electrode is a practical solution. Ir exhibits excellent catalytic activity for hydrogen evolution reactions (HER), and hydrogen oxidation reactions (HOR), yet irreversibly converts to amorphous IrOx at potentials > 0.8 V/RHE, which is an excellent catalyst for oxygen evolution reactions (OER), yet a poor HER and HOR catalyst. Harnessing the multifunctional catalytic characteristics of Ir, here we design a unique Ir-based electrocatalyst with high crystallinity for OER, HER, and HOR. Under OER operation, the crystalline nanoparticle generates an atomically-thin IrOx layer, which reversibly transforms into a metallic Ir at more cathodic potentials, restoring high activity for HER and HOR. Our analysis reveals that a metallic Ir subsurface under thin IrOx layer can act as a catalytic substrate for the reduction of Ir ions, creating reversibility. Our work not only uncovers fundamental, uniquely reversible catalytic properties of nanoparticle catalysts, but also offers insights into nanocatalyst design. Reversible multifunctionality in electrocatalysts can allow voltage reversal during device operation. Here, authors design a crystalline Ir-based electrocatalyst with a thin reversible metallic-Ir/IrOx layer that shows activity for O2 evolution, H2 evolution, and H2 oxidation. [ABSTRACT FROM AUTHOR]

Li-intercalation and -deintercalation effects on the magnetic properties of defect-rich (DR) and defect-suppressed (DS) MoS2 nanosheets are investigated. Active defect sites take large Li (x ≈ 2 in LixMoS2) for DR-MoS2 compared to that for the DS-MoS2 (x ≈ 1.6). Li intercalation brings phase transition from 2H-MoS2 to 1T-LixMoS2 associated with a change in the spin state from spin (S) = 0 Mo4+ in trigonal prismatic geometry (TPG) to S = 3/2 Mo3+ in octahedral geometry (OG). Despite this phase transition, Mo5+ at the defect sites continues to stabilize in the TPG coordination with a change in the oxidation state to Mo4+, giving a net magnetic moment (m) of 0 μB. In contrast, Mo3+ in MoS2 yields m = 3 μB upon Li intercalation. These structural and chemical changes are consistent with the magnetic properties, with DR-MoS2-500 showing four times enhancement in saturation magnetization (MS) at 5 K (from 0.1 to 0.4 emu/g) upon Li intercalation. In contrast, DS-MoS2-900 exhibits low MS = 0.028 emu/g and shows one order increase in MS = 0.21 emu/g upon Li intercalation. Delithiation retains a significant fraction of Li at the defect sites. Distorted OG (DOG) with S = 1 Mo4+ still provides a ferromagnetic state for delithiated MoS2 nanosheets. This study reveals a favorable ferromagnetic ground state of the 1T phase, facilitating much larger magnetization in lithiated MoS2 nanosheets. Ferromagnetic contributions in pristine, lithiated, and delithiated MoS2 arise from S = 1/2 Mo5+ in TPG, S = 3/2 Mo3+ in OG, and S = 1 Mo4+ in DOG, respectively. In all of these cases, a bound magnetic polaron (BMP) is formed with spins from Mo-ions and trapped carriers present at the sulfur vacancies, and the extent of the BMP overlap seems to decide the magnetization values. The enhanced ferromagnetism demonstrated here paves the way for two-dimensional (2D) functional spintronics-based device applications. [ABSTRACT FROM AUTHOR]

In this study, we analyze the properties of boron isotope (11B)‐rich powders from three different sources, that is, American, Cambridge, and Pavezyum, to fabricate the bulk Mg11B2 superconductors and evaluate their superconducting properties. While 11B‐rich powder is an essential precursor to fabricate Mg11B2 superconductors for fusion magnet applications, the properties of the 11B powder turned out to be critical to determine the quality of the final superconducting product. Therefore, appropriate control of processing conditions is needed to comply with the requirements of the nuclear fusion application. Analysis of the B isotope ratio by accelerator mass spectroscopy and neutron transmission revealed that all three types of powder are enriched with 11B to better than 99 at % quality. In addition, Pavezyum's 11B shows the lowest crystallinity and smallest crystalline domain size as evidenced by the high‐resolution X‐ray diffractometer and scanning electron microscopy. The chemical states of the boron isotope investigated with near edge X‐ray absorption fine structure spectroscopy and X‐ray photoemission spectroscopy also reveals that Pavezyum boron has amorphous structure. Mg11B2 bulks and multi‐filamentary (12‐filament) wires have been manufactured, sintered at different temperatures and characterized via the transport critical current density. The wire with Pavezyum 11B shows three times higher current carrying capacity at a particular magnetic field compared to the wire using Cambridge 11B and hence, Pavezyum 11B boron has the potential for manufacturing fusion grade Mg11B2 based magnets. The results of this study demonstrated that Boron powders with higher purity, smaller grain size and lower crystallinity are critical for improving the superconducting and electronic properties of Mg11B2 samples fabricated from the powder. Thus, the low‐neutron‐activation Mg11B2 is possibly an affordable and technically viable candidate to replace NbTi superconductors in the low field poloidal field and correction coils for the next‐generation fusion reactors. [ABSTRACT FROM AUTHOR]

Complex cation distribution in spinel solid solution, fosters defect generation and permutates the optical properties. To scrutinize the effect on structural properties, viz. the cation distribution and defect states upon substitution of Zn with Mg; and to tune the emission properties, Zn1−xMgxAl2O4 (0.01 ≤ x ≤ 0.30) nanocrystals are synthesized. The nanocrystals show increased inversion and generation of multiple defects, namely zinc vacancies, zinc interstitials, oxygen vacancies and antisite defects with increasing Mg content, which thereby impacts the optical band gap. Pentahedral coordination in addition to tetra- and octahedral coordination of Al has been observed, which infers the presence of oxygen vacancies and dangling bonds. Moire fringes formation has intimated the presence of two or more crystal lattices with higher Mg substitution. Band-to-band and defect-assisted photoluminescence shows the role of multiple defects, especially defect clusters, in deciphering the properties of the resulting crystals. Color change from bluish-white to pink has been achieved depending upon the excitation wavelength and emission mechanism, as proposed through a band model schematic. The presented study may be beneficial for designing the Zn1−xMgxAl2O4 nanocrystals with optimized emission properties. [ABSTRACT FROM AUTHOR]

Hydrogen peroxide production by enhanced electrocatalysts is an attractive alternative to the present commercial process. While the subnano/atomic dispersion in noble metal nanocatalysts is known to strongly enhance their catalytic efficiency and chemoselectivity, their excessive surface energy and consequent coarsening seriously compromise their physical/chemical stability. Here, we report a subnano/atomically dispersed Pt–Ag alloy (by a simply modified polyol process) that is resistant to agglomeration/Ostwald ripening. This catalyst does not follow a conventional four-electron oxygen reduction reaction (ORR) but selectively produces H2O2 without excessive degradation of its activity. We clarified the role of the alloying element, Ag, as follows: (1) selective activation of two-electron ORR by inhibiting O2 dissociation and (2) suppression of H2O2 decomposition by preventing the H2O2 adsorption. The present approach provides a convenient route for the direct generation of H2O2 as a simple byproduct of electricity generation by fuel-cell systems. [ABSTRACT FROM AUTHOR]

Using interfacial polymerization (IP) of m‐phenylenediamine aqueous solution containing polyoxovanadate nanoclusters (POV) and trimesoyl chloride (TMC) in organic solution, we fabricated a novel polyamide (PA)‐ polyoxovanadate nanocluster (POV) nanocomposite membranes (PA‐POV TFN). The chemical structures and morphologies of the synthesized membranes were characterized by Fourier transform infrared (FTIR) spectroscopy, atomic force microscope (AFM), scanning electron microscopy (SEM) and water contact angle measurements. Experimental results showed that the performances of PA‐POV TFN membranes are remarkably dependent on POV incorporation in the membranes, which could be controlled by using different amounts of POV particles. Moreover, the PA‐POV TFN membranes illustrated outstanding antibacterial properties against Gram‐negative E. coli. On the other hand, the incorporation of various amounts of POV in the membranes improved the membrane separation performances (water flux and salt rejection) as well as the antibacterial activity in FO process as compared to the original thin‐film composite (TFC) polyamide membrane. [ABSTRACT FROM AUTHOR]

Regardless of much curiosity in the synthesis and diversifying properties of the polymorphs of gallium oxide, they are still unrevealed due to their nanoscale size and structural disorders. In this study, convincing methods have been applied to achieve various phases of gallium oxide (i.e., GaOOH, α-Ga2O3, β-Ga2O3, γ-Ga2O3, δ-Ga2O3, and ε-Ga2O3). X-ray diffraction (XRD) along with Rietveld refinement has been employed to investigate the structural parameters of barely reported phases. Transmission electron microscopy (TEM) images reveal the impact of the protocols of chemical synthesis on the morphology/size of the polymorphs of gallium oxide. Mechanistic discussion on the formation of nano-rod morphology in some of the phases (GaOOH and α-Ga2O3) and nano-particle morphology in other (β-Ga2O3, γ-Ga2O3, δ-Ga2O3 and ε-Ga2O3) phases is also provided by considering the experimental parameters. The existence of Ga3+ ions and their local hybridization with the oxygen is investigated using the X-ray absorption spectroscopy (XAS) at Ga K-edge and conveyed the phase dependence on the hybridization of frontier orbitals. [ABSTRACT FROM AUTHOR]

Defect states in ZnAl2O4 have a significant role in its applicability as a luminescent material. To understand the nature and distribution of defects in its crystal lattice, thermoluminescence (TL) study has been carried out. Excellent TL response is observed from γ- and ultraviolet-irradiated samples at different doses and exposure durations, respectively. Different type of fuels employed in combustion synthesis show a remarkable effect on the trap distribution and hence luminescence properties. Shallow and deep traps are observed in crystals attributed to O− vacancies and F+ centers. The mechanism of trapping, retrapping and recombination have been depicted through schematic band model diagram. X-ray photoelectron spectroscopy indicated the presence of various types of defects specifically AlZn antisite defect, oxygen and zinc vacancies which are further upheld by photoluminescence and Raman spectroscopy. All results when summed up, predict ZnAl2O4 to be a quality material for dosimetry. [ABSTRACT FROM AUTHOR]

For efficient water splitting, it is essential to develop inexpensive and super-efficient electrocatalysts for the oxygen evolution reaction (OER). Herein, we report a phosphate-based electrocatalyst [Fe3Co(PO4)4@reduced-graphene-oxide(rGO)] showing outstanding OER performance (much higher than state-of-the-art Ir/C catalysts), the design of which was aided by first-principles calculations. This electrocatalyst displays low overpotential (237 mV at high current density 100 mA cm−2 in 1 M KOH), high turnover frequency (TOF: 0.54 s−1), high Faradaic efficiency (98%), and long-term durability. Its remarkable performance is ascribed to the optimal free energy for OER at Fe sites and efficient mass/charge transfer. When a Fe3Co(PO4)4@rGO anodic electrode is integrated with a Pt/C cathodic electrode, the electrolyzer requires only 1.45 V to achieve 10 mA cm−2 for whole water splitting in 1 M KOH (1.39 V in 6 M KOH), which is much smaller than commercial Ir-C//Pt-C electrocatalysts. This cost-effective powerful oxygen production material with carbon-supporting substrates offers great promise for water splitting. The sluggish kinetics of the oxygen evolution reaction (OER) is the main obstacle in water splitting which is generally catalyzed by precious metals. Here, authors report a DFT predicted non-precious bimetallic phosphate electrocatalyst that displays high OER activity and stability. [ABSTRACT FROM AUTHOR]

Tetrahedral amorphous carbon (ta-C) film was prepared by the filtered vacuum arc process with Ar background gas. The residual compressive stress of the film decreased significantly as the Ar flow rate increased, whereas negligible change in the mechanical properties was observed. Structure analysis by Raman spectroscopy, near edge x-ray absorption fine structure, and electron spin resonance spectra revealed a close relationship between the residual compressive stress and the bond distortion that invokes paramagnetic defects or unpaired π electrons. These results demonstrate that the stress reduction can occur by relaxation of the distorted or twisted atomic bonds at the same fraction of sp3 hybridized bonds, which enhances the stability of the ta-C coating without deterioration in the advantageous properties. The effect of Ar background gas is discussed in terms of the increased ion population of low kinetic energy in the plasma beam. [ABSTRACT FROM AUTHOR]