Chromium Doping Research Articles

Effect of chromium doping on the grain boundary character of WC-Co

The life of cutting tool inserts is critically important for efficient machining, reducing manufacturing cost, embedded energy, and enabling more complex parts to be machined. For these applications, cemented carbide (WC-Co) materials are a prime candidate. The performance of these materials can be limited by early fracture, typically via an intergranular fracture path with respect to carbide grains. This motivates further studies to understand the character of the grain boundary network so that grain boundary engineering (GBE) of WC-Co tools can be used to improve tool life and performance. In this work, we have used Rohrer et al.'s five-parameter grain boundary character distribution (GBCD) analysis to examine the grain boundary network of WC-10wt%Co and WC-10wt%Co-1wt%Cr samples (Rohrer et al., 2004a [1]). It was found that the measured area fraction of the Σ2 boundaries was comparable to the values reported in the literature despite the relatively larger grain sizes (~14 μm) and higher cobalt contents. The result suggests that chromium doping increases the area fraction of Σ2 boundaries from 12.8 % to 14.8 %. It is proposed that this is a consequence of altering the Σ2 boundary energy, as associated with adding chromium.

Optical sensing and nonlinear optical properties of Cr-doped MoO3/PEDOT:PSS Nanocomposites

In this study, we observed a negative UV photoresponse that switched to a positive photoresponse in Cr-doped MoO3/PEDOT:PSS nanocomposite films(NCF) prepared via drop-casting. MoO3 and Cr-doped MoO3 were synthesized using a hot oil bath co-precipitation method, combined with PEDOT:PSS (poly(3,4-ethylenedioxythiophene) doped with poly(4-styrenesulfonate)), and coated onto flexible OHP sheets. The open aperture z-scan method investigated the nonlinear optical properties of NCF on the glass substrate. The films were characterized by X-ray diffraction, scanning electron microscopic (SEM), UV–Vis spectroscopy, and Fourier Transformed Infrared (FTIR). Chromium doping caused minor changes in lattice parameters, crystalline size, and microstrain. UV spectroscopy revealed an increase in bandgap with higher Cr–MoO3 concentrations. The photoresponse of different Cr–MoO3 concentrations showed an initial current decrease under UV light, but the photoresponse became positive beyond a threshold and continued to improve. Nonlinear optical studies indicated saturable absorption in the nanocomposite. This work enhances our understanding of Cr-doped MoO3/PEDOT:PSS nanocomposites, contributing to advancements in flexible UV photodetectors and nonlinear optical applications.

Electronic vs phononic thermal transport in Cr-doped V2O3 thin films across the Mott transition

Understanding the thermal conductivity of chromium-doped V2O3 is crucial for optimizing the design of selectors for memory and neuromorphic devices. We utilized the time-domain thermoreflectance technique to measure the thermal conductivity of chromium-doped V2O3 across varying concentrations, spanning the doping-induced metal–insulator transition. In addition, different oxygen stoichiometries and film thicknesses were investigated in their crystalline and amorphous phases. Chromium doping concentration (0%–30%) and the degree of crystallinity emerged as the predominant factors influencing the thermal properties, while the effect of oxygen flow (600–1400 ppm) during deposition proved to be negligible. Our observations indicate that even in the metallic phase of V2O3, the lattice contribution is the dominant factor in thermal transport with no observable impact from the electrons on heat transport. Finally, the thermal conductivity of both amorphous and crystalline V2O3 was measured at cryogenic temperatures (80–450 K). Our thermal conductivity measurements as a function of temperature reveal that both phases exhibit behavior similar to amorphous materials, indicating pronounced phonon scattering effects in the crystalline phase of V2O3.

The structural, magnetic and electrical properties of chromium doped calcium ferrite nanoparticles

Calcium ferrite nanoparticles doped with Chromium (10-50 mol %) are synthesized using the solution combustion method, employing citrus Lemon extract as a reducing agent, followed by a calcination process at 500oC. Various characterization techniques are employed on the calcined samples. The Bragg reflections resulting from Chromium doping confirm the formation of a singular orthorhombic calcium ferrite phase. Crystallite sizes determined using both Scherrer’s and W-H plot methods found to be decreases with increase in dopant concentration. The surface morphology showcases agglomerated nanoparticles with irregular shapes and sizes, accompanied by pores and voids. The energy band gap found to be increases with increase in dopant concentration from 2.82 to 2.93 eV. The hysteresis loop analysis provides magnetic parameters including saturation magnetization (Ms), remanence (Mr), and coercivity (Hc). As the dopant concentration increases, Ms and Hc found to be maximum at 30 mol% cr3+ concentration in CaFe2O4 NPs. Linear increase in frequency-dependent conductivity at lower frequencies was observed. The presence of semicircles at low frequencies signifies compliance with the Cole-Cole formula for impedance behavior. Additionally, a detailed discussion on dielectric properties is presented. Notably, the dielectric constant decreases from 4.2 to 2.74 with an increase in dopant concentration. These distinctive attributes position the samples as suitable candidates for memory devices as well as high-frequency device applications.

DFT electronic structure investigation of chromium ion-implanted cupric oxide thin films dedicated for photovoltaic absorber layers

This study explores the enhancement of cupric oxide (CuO) thin films for photovoltaic applications through chromium doping and subsequent annealing. Thin films of CuO were deposited on silicon and glass substrates using reactive magnetron sputtering. Chromium was introduced via ion implantation, and samples were annealed to restore the crystal structure. The optical and structural properties of the films were characterized using X-ray diffraction, spectrophotometry, and spectroscopic ellipsometry. Results indicated that implantation reduced the absorbance and conductivity of the films, while annealing effectively restored these properties. Sample implanted with 10 keV energy and 1 × 1014 cm−2 dose of Cr ions, after annealing had sheet resistance of 1.1 × 106 Ω/sq compared to 1.7 × 106 Ω/sq for non implanted and annealed CuO. Study of crystalline structure confirmed the importance of annealing as it reduced the stress present in the material after deposition and implantation. Density Functional Theory (DFT) calculations were performed to investigate the electronic structure and optical properties of CuO with varying levels of chromium doping. Calculations revealed an energy gap of 1.8 eV for undoped CuO, with significant changes in optical absorption for doped samples. Energy band gap determined using absorbance measurement and Tauc plot method had value of 1.10 eV for as deposited CuO. Samples after implantation and annealing had energy band gap value increased to about 1.20 eV. The study demonstrates that chromium doping and subsequent annealing can enhance the optical and electronic properties of CuO thin films, making them more efficient for photovoltaic applications.

Modeling oxygen transport in Cr doped UO2 fuel with the TAF-ID during power transients

This paper proposes an efficient coupling between an oxygen redistribution model and the Thermodynamics for Advanced Fuels-International Database (TAF-ID) to describe the behavior of fission products, actinides, and dopant in a uranium dioxide matrix. The formulation of oxygen migration in the fuel is a function of the oxygen (and uranium) chemical potential gradient. The proposed formulation does not require the introduction of the Soret term and relies solely on the known mobilities of uranium and oxygen in the fuel. This coupling is applied to the simulation of a power ramp on a chromia-doped fuel rod using the PLEIADES/ALCYONE fuel performance code. The simulations successfully reproduce most of the available experimental observations on the fission products (Cs, Mo, Ru) and on the chromium dopant.

Preparation, Characterization and Optical Analysis of Chromium Doped 45S Bioactive Glass-Ceramic

The 45S Bioactive glass-ceramic (BG) and Chromium (Cr)-doped BG materials were successfully produced in this study. XRD, FTIR, and ICP-MS techniques were used to characterize the prepared materials. The XRD testing showed that all samples contained pure BG. Increased Cr ion inclusion shifted the BG diffraction peaks to a lower value of 2 Theta and increased crystallinity. FTIR was used to detect Si-O, P-O, and Ca-O functional groups. Cr ions steadily decreased the Ca-vibration mode area. The ultraviolet-visible spectrophotometry was used to measure the optical characteristics of pure and Cr BG-doped materials. The Cr-doped BG was green in colour, whereas the lab-synthesized BG was white. Two additional bands formed at 433 and 615 nm when Cr ions were doped into the BG structure. These bands may be caused by 4A2 → 4T1 and 4A2 → 4T2 electronic d-d transitions. The findings show that biomedical applications may exist for fluorescent probes manufactured from Cr-BG materials.

Insights into the compositional and temperature-mediated magnetic characteristics of chromium-doped ZnO nanoparticles

This study explores the influence of chromium content and temperature on the magnetic characteristics of ZnO synthesized via the cost-effective coprecipitation approach. The host ZnO structure is not significantly changed by chromium doping, even at 5 wt.% of chromium concentration, according to x-ray diffraction studies. The Zn–O characteristic stretching vibration band at 480 cm−1 and the other functional group attached to the Cr-doped ZnO nanoparticles are confirmed by Fourier-transform infrared (FTIR) spectroscopy studies. Diffuse reflectance spectroscopy analysis shows the interaction between chromium ions and ZnO causes bandgap narrowing, and the observed optical bandgap values fall as chromium content increases in the host ZnO matrix. Point defects such as zinc interstitial, zinc vacancy, and oxygen vacancy that exist in the Cr-doped ZnO nanoparticles are inveterate through photoluminescence spectroscopy. Vibrating sample magnetometry investigations reveal weak ferromagnetic behavior at low applied fields and diamagnetic signatures dominating at high applied fields in the Cr-doped ZnO nanoparticles at 300 K. The magnetic characteristics are also tunable in terms of temperatures, which opens new avenues for fabricating dilute magnetic semiconductors with various applications.

In situ Mössbauer spectroscopy study of the activation and reducibility of chromium- and aluminium-doped iron oxide based water-gas shift catalysts under industrially relevant conditions

The influence of chromium and aluminium doping on the over-reduction during activation of iron-oxide-based water-gas shift catalysts was investigated using Mössbauer spectroscopy for the first time. In situ Mössbauer spectra of catalysts exposed to industrially relevant gas compositions were recorded with increasingly reducing R factors R = [CO]*[H2]/[CO2]*[H2O]. Whereas α-Fe and cementite formed during exposure of a non-doped iron-oxide catalyst to process conditions with an R factor of 2.09, such phases were only observed at R = 4.60 for a chromium-doped catalyst, showing that chromium stabilizes the catalyst. Over-reduction was enhanced to R = 2.88 in a chromium-copper co-doped catalyst. α-Fe was already observed at R = 1.64 in an aluminium-doped catalyst, while cementite formation occurred at R = 2.09, showing that over-reduction was enhanced, the presence of aluminium delaying carburization. Co-doping copper in the aluminium-doped catalyst showed cementite formation at R = 2.09, the same as a non-doped catalyst.

O‐2p Hybridization Enhanced Transformation of Active γ‐NiOOH by Chromium Doping for Efficient Urea Oxidation Reaction

AbstractThe electrooxidation of urea holds great potential for converting urea from wastewater into hydrogen, contributing to environmental protection and sustainable energy production. This necessitates the development of highly efficient and stable catalysts for the urea oxidation reaction (UOR). In this study, a NiCoCr‐LDH/NF (nickel‐cobalt‐chromium layered double hydroxide/nickel foam) electrode is successfully synthesized via a simple hydrothermal method, demonstrating excellent electrocatalytic performance with a low work potential of 1.38 V at a high current density of 100 mA cm−2. In situ, Raman spectra analysis revealed that the incorporation of chromium (Cr) facilitated the generation of active γ‐NiOOH species and catalyst reconstruction. Density functional theory (DFT) simulations confirmed that the lower formation energy of γ‐NiOOH is due to the weakened interaction of O─H bonds because of a narrow energy range of hybridization between O‐2pz orbitals and H‐1s orbitals. The introduction of Cr also improved the adsorption energy of urea molecules and its intermediates, thereby enhancing the overall activity of UOR. With its excellent electrocatalytic performance, unique electronic states, and coordination structures, the NiCoCr‐LDH/NF electrode showcases great potential for practical applications in the field of energy catalysis.

Highly efficient anion exchange membrane water electrolyzers via chromium-doped amorphous electrocatalysts

In-depth comprehension and modulation of the electronic structure of the active metal sites is crucial to enhance their intrinsic activity of electrocatalytic oxygen evolution reaction (OER) toward anion exchange membrane water electrolyzers (AEMWEs). Here, we elaborate a series of amorphous metal oxide catalysts (FeCrOx, CoCrOx and NiCrOx) with high performance AEMWEs by high-valent chromium dopant. We discover that the positive effect of the transition from low to high valence of the Co site on the adsorption energy of the intermediate and the lower oxidation barrier is the key factor for its increased activity by synchrotron radiation in-situ techniques. Particularly, the CoCrOx anode catalyst achieves the high current density of 1.5 A cm−2 at 2.1 V and maintains for over 120 h with attenuation less than 4.9 mV h−1 in AEMWE testing. Such exceptional performance demonstrates a promising prospect for industrial application and providing general guidelines for the design of high-efficiency AEMWEs systems.

Tuning the electrochemical properties of ZnO through chromium doping and its suitability for supercapacitor application

ZnO nanoparticles doped with chromium (Cr) were synthesized through a simple sol gel route. The successful Cr doping into the ZnO lattice has been evidenced via several characterisation techniques i.e., XRD and XPS. A high oxygen vacancies (OV) density has been located through Photoluminescence (PL) and EPR studies for the Cr doped ZnO (1 %) (ZnCr1) sample. The high density of OV defects induced from Cr doping in ZnO lattice was considered at the origin of the improved electrochemical performances by promoting efficient electron transfer ability with intercalation process of the electrolyte's ions during charge-discharge mechanism. The ZnOCr1 electrode displays an important capacitance value (367 F.g−1), ultrahigh capacitance retention (86 %) while changing the current from 1 to 20 A·g−1, and marvellous stability of 84 % during 4000 cycles. An asymmetric supercapacitor based ZnOCr1 electrode achieves significant potential window up to 1.6 V with encouraging specific energy density. The device showcases a satisfactory specific energy of 27.1 Wh·Kg−1 at specific power of 480 W·Kg−1 and a great retention of 17 % decay after 4000 cycles at current density of 10 A g−1. This opens door to the developed ZnO-Cr1 material for its application in future supercapacitor devices.

Comparison activity of pure and chromium-doped nickel oxide nanoparticles for the selective removal of dyes from water

The current study involves a synthesis of a composite of nickel oxide nanoparticles (NiONPs) with a chromium dopant to yield (Cr/NiONPs). Synthesis of nickel oxide was performed by the co-precipitation method. The synthesis of the composite was conducted by the impregnation method. FTIR, EDX, SEM, and XRD were used to characterize the synthesized materials. The synthesised materials’ point zero charges (PZC) were performed using the potentiometric titration method. The obtained results show that the PZC for neat nickel oxide was around 5, and it was around 8 for Cr/NiONPs. The adsorption action of the prepared materials was examined by applying them to remove Reactive Red 2 (RR2) and Crystal Violate (CV) dyes from solutions. The outcomes demonstrated that Cr/NiONPs were stronger in the removal of dyes than NiONPs. Cr/NiONPs achieved 99.9% removal of dyes after 1 h. Adsorption isotherms involving Freundlich and Langmuir adsorption isotherms were also conducted, and the outcomes indicated that the most accurate representation of the adsorption data was offered by Langmuir adsorption isotherms. Additionally, it was discovered that the adsorption characteristics of the NiONPs and Cr/NiONPs correspond well with the pseudo-second-order kinetic model. Each of the NiONPs and Cr/NiONPs was reused five times, and the results display that the effectiveness of the removal of RR2 dye slightly declined with the increase in reuse cycles; it lost only 5% of its original efficiency after the 5 cycles. Generally, Cr/NiONPs showed better reusability than NiONPs under the same conditions.

Challenges in power scaling of Cr:LiCAF lasers: effect of passive losses.

In this work, we have investigated the continuous-wave (cw) lasing potential of thin slab-shaped Cr:LiCAF crystals with a low chromium doping level of around 1% and various lengths of 1 to 2cm. These relatively long crystals with low Cr-doping facilitate the distribution of heat load in a larger volume and could enable power scaling of Cr:LiCAF lasers. However, long crystals tend to have larger passive losses, and it is also more challenging to achieve efficient mode-matching to the low-brightness pump mode in a longer gain element, which could hinder laser performance. To explore the issue, we have performed detailed cw lasing experiments in single- and multimode diode-pumped Cr:LiCAF laser systems employing crystals with different doping and length. Our results showed that current state-of-the-art crystal growth methods provide Cr:LiCAF crystals with low enough passive losses to enable cw laser efficiencies of up to 50%, even in these long samples. The pump powers available in this study (5.35W) limited the cw powers we could achieve experimentally to 2.25W level; however, our simulations indicate that thin slab-type Cr:LiCAF crystals with low Cr-doping have the potential to achieve cw powers above 10W level.

Exploring the effect of chromium doping on electronic properties, half-metallic and ferromagnetism on AlSb DMS compound through first-principles calculations

With the aim of improving and investigating magnetocaloric insights for spintronic applications, we investigated the electronic structure of Cr-doped AlSb compounds via first-principles calculations using the KKR-CPA-DFT method. Here, we investigated the stability of alloy materials as a function of magnetic contamination. A stable semimetallic ferromagnetic phase can be obtained by introducing the Cr element into AlSb, which is inherent in nonmagnetic semiconductors. The total magnetic moment of the doped material changes from 0.1167 μB to 0.716 μB for 4% and 25% Cr, respectively. Curie temperature changed to 740 K at 25% Cr concentration.
 KEY WORDS: Magnetic materials, Semiconductor, Alloys, Impurities
 Bull. Chem. Soc. Ethiop. 2024, 38(2), 297-304. 
 DOI: https://dx.doi.org/10.4314/bcse.v38i2.2

Promoted electro-oxidation kinetics in chromium-doped α‑Ni(OH)2 nanosheets for efficient selective conversion of methanol to formate

Owing to the elusive pathways of methanol oxidation reaction (MOR) and the lack of applicable catalysts, the selective electro-oxidation of methanol to formate remains a challenging topic. Herein, we present a chromium-doping strategy to promote the MOR performance of α-Ni(OH)2 nanosheets with a high selectivity towards formate generation. Taking chromium-doped α-Ni(OH)2 nanosheets as an example, we further highlight the role of doping atoms in MOR by combining theoretical calculations with experimental measurements. It reveals that chromium doping can not only enhance the conductivity of α-Ni(OH)2 nanosheets, but also endow the catalyst with optimized kinetics for electroactive NiOOH formation and methanol absorption, thus resulting in a remarkable MOR current density of 141 mA cm−2 at 0.50 V vs. Ag/AgCl with a faradaic efficiency of 92.1% for formate. Furthermore, in situ infrared spectroscopy demonstrates that methanol is selectively oxidized to formate without further oxidation to CO2 over chromium-doped α‑Ni(OH)2 nanosheets in alkaline media.

First-principles calculations to investigate chromium doping effect on structural, elastic, electronic, magnetic and optical properties on the high matrix CaTe

First-principles calculations to investigate chromium doping effect on structural, elastic, electronic, magnetic and optical properties on the high matrix CaTe

Cost effective Cr-doped Co(OH)2 nano-flower assemblies exhibiting excellent electrochemical performance for supercapacitors

Chromium doping along with topology, the nano-flowers exhibit exceptional electrochemical performance. By systematically characterizing the prepared samples of pristine Co(OH)2 and Cr doped Co(OH)2 using a comprehensive series of analytical techniques, including XRD, SEM, TEM, EDX, FTIR, and PL, a profound understanding of their structural and morphological features is achieved. Paving the path for significant advancements in renewable energy storage technology exploration for prime and cost-effective electrode materials for supercapacitors is a major challenge. This paper presents an innovative study on Cr doped Co(OH)2 based nano-flowers. The synergistic role of the average size of fibrous structures comprising nano-flowers is in the range of 20 nm showing high surface area of the prepared sample. Electrochemical performance was acquired in 2 M KOH electrolyte by CV, GCD and EIS. To understand the rate of ion transport within the sample, diffusion coefficient has been calculated. The discernible improvement in redox behavior, maximize the capacitance of 3 % Cr-Co(OH)2 to 1252 Fg−1 and diffusion coefficient to 1.509 × 10−5 cm2s−1. Furthermore, the power law unveils the pseudocapacitive nature of 3 % Cr-Co(OH)2 electrode material and unprecedented cyclic stability by possessing retention rate of 93 % even after 5000 cycles. All these calculated properties exhibit the immense potential of doped nano-flowers as a reliable source of high-energy electrode material.

Effect of chromium doping on the band gap tuning of titanium dioxide thin films for solar cell applications

A simple and inexpensive spray pyrolysis deposition (SPD) approach was used to produce TiO2 and Cr (2–8) at.%-doped TiO2 thin films. To explore the morphological features of the films, FE-SEM micrographs were used and found that 6 and 8 at.% TiO2:Cr films had fibrous patterns with diameters of 0.45 and 0.78 μm, respectively, while the remainder of the films were agglomerated particles. From X-ray diffraction investigation, it was found that the TiO2 thin films had an anatase crystal phase (tetragonal) up to 6 at.% Cr doping, while an anatase-rutile mixed crystalline phase was identified for 8 at.% Cr doping. The crystallite size of the pristine TiO2 film was 35 nm, while for TiO2:Cr films, it ranges from 35 to 46 nm. The Fizeau fringes technique was employed to measure the thickness of the TiO2 film and 165 nm was found for pristine TiO2 and 164–180 nm for TiO2:Cr films. UV–visible spectroscopy was used to study optical properties such as absorbance, refractive index, optical band gap, dielectric constant, and optical conductivity. As the Cr concentration increases, the optical band gap decreases from 3.40 eV to 2.70 eV. Using the four-point probe method, it was found that the resistivity changes with temperature and is also affected by the Cr content.

Enhancing tribological performance of graphene sheet-embedded carbon films on steel substrates via texture engineering and chromium doping

Amorphous carbon (a-C) film is a promising solid lubricant coating due to its unique structure and excellent properties. However, its poor adhesion and long running-in period hinder the application in metal components. Graphene sheet-embedded carbon (GSEC) film has a significantly shorter running-in period but suffers from inferior tribological properties due to its rough surface and weak mechanical characteristics. In this study, we utilized an electron cyclotron resonance (ECR) plasma nano-surface manufacturing device to deposit GSEC films onto steel substrate surfaces. By manipulating the surface/interface texture and incorporating chromium (Cr) doping, the tribological properties of the GSEC films were improved both chemically and physically. The results demonstrated that the textured carbon film exhibited superior adhesion to the steel substrate and a wear life that was three orders of magnitude longer than the untextured GSEC film, under low normal load conditions while sliding against the GCr15-bearing steel ball. After doping the Cr into textured carbon films, there was a significant reduction in the friction coefficients, and the wear type of carbon film transformed from adhesive wear to abrasive wear. Moreover, the doped carbon films demonstrated prolonged wear lives under high normal loads. This improvement can be attributed to the formation of hard CrC nanocrystalline, which effectively reduced surface roughness and enhanced the mechanical properties of the carbon films. Notably, even under a contact pressure of 0.83 GPa, the doped carbon film maintained favorable tribological performances. These findings have extended the potential applications of carbon films on metal substrates.